International Journal of Powder Metallurgy Volume 43 Issue 5

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International Journal of POWDER METALLURGY

powder metallurgy September/October 2007 INTERNATIONAL

Focus Issue: Copper PM—New Developments & Applications

43/5 September/October 2007

43/5 Newsmaker: Chaman Lall PM Copper: Beyond Self-Lubricating Bearings Electronic Applications for Copper Powder Copper-Base PM—Past, Present & Future MIM of Copper and Copper Alloys for Microelectronic Heat Dissipation

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EDITORIAL REVIEW COMMITTEE P.W. Taubenblat, Chairman I.E. Anderson, FAPMI T. Ando S.G. Caldwell S.C. Deevi J.J. Dunkley W.B. Eisen Z. Fang B.L. Ferguson W. Frazier K. Kulkarni, FAPMI K.S. Kumar T.F. Murphy P.D. Nurthen J.H. Perepezko P.K. Samal H.I. Sanderow D.W. Smith, FAPMI J.E. Smugeresky R. Tandon T.A. Tomlin D.T. Whychell, Sr., FAPMI M. Wright, PMT A. Zavaliangos INTERNATIONAL LIAISON COMMITTEE D. Whittaker (UK) Chairman V. Arnhold (Germany) E.C. Barba (Mexico) P. Beiss (Germany) C. Blais (Canada) P. Blanchard (France) G.F. Bocchini (Italy) F. Chagnon (Canada) C-L Chu (Taiwan) H. Danninger (Austria) U. Engström (Sweden) N.O. Grinder (Sweden) S. Guo (China) F-L Han (China) K.S. Hwang (Taiwan) Y.D. Kim (Korea) G. Kneringer (Austria) G. L’Espérance, FAPMI (Canada) H. Miura (Japan) C.B. Molins (Spain) R.L. Orban (Romania) T.L. Pecanha (Brazil) F. Petzoldt (Germany) S. Saritas (Turkey) G.B. Schaffer (Australia) Y. Takeda (Japan) G.S. Upadhyaya (India) Publisher C. James Trombino, CAE [email protected] Editor-in-Chief Alan Lawley, FAPMI [email protected] Managing Editor Peter K. Johnson [email protected] Advertising Manager Jessica S. Tamasi [email protected] Copy Editor Donni Magid [email protected] Production Assistant Dora Schember [email protected] President of APMI International Nicholas T. Mares [email protected] Executive Director/CEO, APMI International C. James Trombino, CAE [email protected]

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43/5 September/October 2007

Editor's Note Newsmaker Chaman Lall PM Industry News in Review PMT Spotlight On … Ken Watson Consultants’ Corner Olle Grinder

17 PM Metallography Competition Grand Prize FOCUS: COPPER PM—NEW DEVELOPMENT & APPLICATIONS 23 Expanding the Market for PM Copper: Beyond SelfLubricating Bearings P. Taubenblat

31 Electronic Applications for Copper Powder J.A. Shields, Jr. and I. Smid

43 Copper-Base PM—Past, Present & Future W. Ullrich

55 Metal Powder Injection Molding of Copper and Copper Alloys for Microelectronic Heat Dissipation R.M. German and J.L. Johnson

64 Advertisers’ Index

Cover: PM Metallography Competition Winner. Photo courtesy Christopher T. Schade, Hoeganaes Corporation, Cinnaminson, New Jersey The International Journal of Powder Metallurgy (ISSN No. 0888-7462) is a professional publication serving the scientific and technological needs and interests of the powder metallurgist and the metal powder producing and consuming industries. Advertising carried in the Journal is selected so as to meet these needs and interests. Unrelated advertising cannot be accepted. Published bimonthly by APMI International, 105 College Road East, Princeton, N.J. 08540-6692 USA. Telephone (609) 4527700. Periodical postage paid at Princeton, New Jersey, and at additional mailing offices. Copyright © 2007 by APMI International. Subscription rates to non-members; USA, Canada and Mexico: $90.00 individuals, $210.00 institutions; overseas: additional $35.00 postage; single issues $45.00. Printed in USA by Cadmus Communications Corporation, P.O. Box 27367, Richmond, Virginia 23261-7367. Postmaster send address changes to the International Journal of Powder Metallurgy, 105 College Road East, Princeton, New Jersey 08540 USA USPS#267-120 ADVERTISING INFORMATION Jessica Tamasi, APMI International INTERNATIONAL 105 College Road East, Princeton, New Jersey 08540-6692 USA Tel: (609) 452-7700 • Fax: (609) 987-8523 • E-Mail: [email protected]

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EDITOR’S NOTE

H

istorically, the powder metallurgy (PM) of copper has been synonymous with the self-lubricating bearing (SLB), reflecting a share of more than 50% of the total copper PM market. This scenario is changing as China’s impact on global copper PM increases. Forecasts vary, but an annual growth rate for total global copper PM approaching 6% appears realistic over the next four years. Significantly, this growth will be vested primarily in new non-structured applications. To put the dynamic in perspective, Taubenblat has coordinated this Focus Issue on new developments and applications in copper PM. His overview of the expanding market beyond SLBs is followed by in-depth assessments of metal injection molding for the fabrication of copper and copper alloys in microelectronic heat-dissipation applications (German and Johnson), and of electronic applications utilizing copper powder (Shields and Smid). Ullrich reviews the press-and-sinter copper PM landscape, with a focus on new products based on aluminum bronzes and spinodal alloys. A “welcome back” to Olle Grinder in the “Consultants’ Corner.” His expertise in PM processing is evident in detailed answers to readers’ questions on the selection of tool materials and on the avoidance of gross surface defects during compaction. Chaman Lall is Peter Johnson’s featured “Newsmaker.” After receiving a doctoral degree in metallurgy from my alma mater, his career in the PM industry has embraced gas atomization, ferrous parts fabrication, aluminum PM, metal and ceramic injection molding, high-temperature and vacuum sintering, soft magnetic materials, and stainless steels. The Grand Prize (submitted in the Student category) in the APMI 2007 PM Metallography Competition is recognized. The front cover (another competition winner, in the Artistic category) illustrates the intrinsic aesthetics of a PM material. Other winning entries, to be featured in future issues, exemplify the utility of metallography as a problem solving methodology in PM.

Alan Lawley Editor-in-Chief

Many of my colleagues in the PM community are aware that I have, for whatever reasons, long been a banana junkie. While it is well known that the banana is rich in potassium and is an excellent source of energy in our quest to keep fit, it offers many other lesser-known virtues. I am indebted to Kemp Roll for forwarding a recent and fascinating “profile” of the banana. There is persuasive evidence that the banana enhances brain power—while it combats/reduces depression, PMS, anemia, high blood pressure, constipation, hangovers, heartburn, morning sickness, mosquito bites, nerves, obesity, smoking, ulcers, stress, and strokes. It is even claimed that warts are removed by contact with the inside of a banana skin. After reading the complete “profile” (http://www.finetuneyou.com/Bananas.html) you will probably never look at a banana the same way again. Perhaps bananas are the reason that monkeys always appear to be happy!

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Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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NEWSMAKER

CHAMAN LALL By Peter K. Johnson* Chaman Lall, vice president of applications development, Metal Powder Products Company (MPP), Westfield, Indiana, says, “The joy of my job is my diverse responsibilities, which encompass assisting in new business development, material and process developments, and applying sound management practices throughout our corporation.” Growing up in an immigrant community in Birmingham, England, could have directed Lall to a very different career path. “Destiny takes you places,” he says. His family immigrated to England from Punjab, India, when he was seven. Without outside influences his career options were limited to pursuing a similar route as his father and finding a position in a factory. “I had no interest in furthering my studies,” he recalls. As the eldest son in a close-knit family, Lall wanted to join the workforce in order to assist with the family’s expenses. However, high school science teachers and a mentor in the St. John’s Ambulance Brigade, a first-aid volunteer group, encouraged Lall to pursue higher education. He felt fortunate to land a laboratory technician’s job at the University of Birmingham Metallurgy Department. While working there and living at home, he attended a technical college in the evenings for three years in preparation for enrolling in the university’s undergraduate program. “I loved solid-state physics and relating it to understanding the physical universe,” he says. His BS in metallurgy was awarded with honors, which opened the door to a fast-track PhD program in physical metallurgy and materials. He was mentored by Professors Ray Smallman and Mike Loretto as he studied deformation characteristics of the ordered Zr-Co-Ni alloy system, using one of the first million-volt transmission electron *Managing editor and consultant

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

microscopes in the country. In 1976 he earned his PhD in metallurgy. Lall’s interest in powder metallurgy (PM) did not really click until he joined a PM research team at Drexel University in 1978. He had moved to Philadelphia in 1976 with his wife and two young children. During that time, England was fighting a recession that produced a gloomy employment scene for metallurgists. He began his professional career in the United States with a postdoctoral research associate position at the University of Pennsylvania studying deformation characteristics as a function of temperature of single crystal silicon and Ni3Al, a key component of superalloys used in jet engines. At the conclusion of his postdoctoral project, Professor Diran Apelian invited Lall to join a two-year research project on gas atomization and diffusion solidification at Drexel University. A door to the real world of PM parts manufacturing opened in January, 1980, when Lall was offered the role of senior metallurgist in the PM group of Remington Arms in Ilion, New York. He worked for Louis Baum and Hal Munson, learning about production problem solving, quality issues, new part development, soft magnetism, stainless steels, high-temperature sintering, and metal injection molding (MIM). Close collaboration between Remington and RPI presented opportunities to fund research work with Professors Fritz Lenel and Rand German on special PM projects. Remington was owned by DuPont, which led to Lall’s transfer to the chemical company’s R&D labs in Wilmington, Delaware. “I worked on developing the ceramic injection molding (CIM) process, collaborating with world-renowned organic chemists,” he says. “We developed a binder sysijpm

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NEWSMAKER: CHAMAN LALL

tem, which was an integral part of a CIM process that demonstrated the ability to hold tight dimensional tolerances on ceramic components made for the Textile Fibers Division of DuPont. It was a great learning experience that taught me much about the application of organic chemistry to formulating stable suspensions and emulsions.” In 1986 Lall returned to conventional PM via Remington’s Hazen, Arkansas, plant where he assumed product and business development responsibilities. DuPont provided ample opportunities for training, which were to prove invaluable in later years; this included management for organizational effectiveness, competitive benchmarking, and product and brand marketing. However, commuting between Delaware and Arkansas took its toll, especially when Lall was asked to relocate there. A new opportunity opened up in 1989, when Herbert Tews, president of Midwest Sintered Products (MSP), Riverdale, Illinois, invited Lall to join his company as director of engineering, because of Lall’s expertise in vacuum sintering and soft magnetic materials. Increasing management responsibilities led to Lall being named vice president in 1992, assuming all operational

responsibilities for the company. MSP was later purchased by Sinter Metals Inc., which was subsequently acquired by GKN. Concerned about the bureaucracy of the new, much larger corporate structure, Lall accepted a position with MPP, which initially wanted to utilize his MIM expertise, but the company eventually exited the MIM business. Lall tapped into his extensive conventional PM and management expertise and carved out a new role as MPP’s chief technology officer. As a senior member of MPP’s management team, his professional activities have included strategic planning, contract negotiations, business and applications development, and the establishment of a technology center. He is the primary liaison for consortia research activities with the Center for Powder Metallurgy Technology and Worcester Polytechnic Institute. Working for a multi-plant company, Lall has introduced scientific discipline to PM parts manufacturing, especially aluminum PM. “Furthermore,” he says, “we are developing lightweight aluminum components using unique composites.” He has also helped commercialize a proprietary forming process to make specific gear forms with tooth densities of

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NEWSMAKER: CHAMAN LALL

more than 7.7 g/cm3. “We have developed products with properties superior to those of wrought heat treated AISI 8620 steel, and surface-densification processes such as gear rolling that can enhance fatigue performance”, he adds. “The challenge is to convince the marketplace to accept the data and validate product performance on specific components. The problem is that such validations can take months and even years.” Industry involvement is another important pursuit. Lall co-chaired the 1994 Inter national Conference on Powder Metallurgy & Particulate Materials, has served on the MPIF Technical Board and MPIF Standards Development Board, has attended MPIF Management and Technical Conferences, and has presented papers at numerous conferences and short courses. “MPIF and APMI have given me a tremendous opportunity to mingle with industry people at all levels,” he notes. “I have fond memories of attending conferences and networking at standards meetings, allowing me the privilege of meeting some of the finest people in the world. Lanny Pease and Diran Apelian are right up there on that list.” He edited the

recently-released MPIF literature CD, The Science of Stainless Steels Produced by Powder Metallurgy and Metal Injection Molding. His monograph Soft Magnetism Fundamentals of Powder Metallurgy and Metal Injection Molding has been a soughtafter publication by both PM professionals and customers alike. Lall envisions a bright future for powder metallurgy but believes that more emphasis should be given to customer education about PM’s value. “There is too much emphasis on PM as a cheap product,” he says. “The industry should talk more about the performance of products and the solutions to customer design and application issues. PM is a fabulous fabrication technology that can supply high-performance, intricate components and material combinations that competing technologies cannot.” Outside of PM, Lall leads a well-rounded life with interests, spanning photography, English and Asian music, badminton, and tennis. His family is also very important to him, and he credits the strong support of his wife Samitra in his career and in nurturing their four children, ages 31 to 21. ijpm

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1403 Fourth St. • Kalamazoo, MI 49048 • Tel: 269-342-0183 Robert Lando E-mail: [email protected] Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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International sophistication. Powder injection molding (PIM) enables complex ceramic and metal products to be produced in large volumes. Complex parts with a special design, high surface quality and dimensional stability can be produced in a single step, thus dispensing with time and cost-intensive post-processing steps. If you want to find out more about powder injection molding - ask the leading international experts in our PIM laboratory!

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PM INDUSTRY NEWS IN REVIEW The following items have appeared in PM Newsbytes since the previous issue of the Journal. To read a fuller treatment of any of these items, go to www.apmiinternational.org, login to the “Members Only” section, and click on “Expanded Stories from PM Newsbytes.”

Union Process Completes Expansion Union Process, Inc., Akron, Ohio, has completed a 6,000 sq. ft. expansion to handle its growing toll milling business. The company also supplies attritors, additional grinding equipment, grinding media, lab services, and reconditions attritors. PM Tooling Clamps Available Quala-Die, Inc., St. Marys, Pa., has designed Q-Clamps made from metal powder as alternative to machined hardware. The company makes PM tooling and provides precision machining services.

die cast valve bodies, and powder metallurgy (PM) parts. Plansee Group Sales Rise The Plansee Group, Reutte, Austria, reported fiscal year 2006/2007 sales increasing by 13 percent to 971 million euros. The company invested a record 121 million euros in production sites, facilities, and new products. Sales and Earnings Rise at Höganäs AB Höganäs AB, Sweden, reports that net sales for the first six months of 2007 advanced 12 percent to MSEK 2,931 (about $440 million). Earnings rose 15 percent to MSEK 341 (about $51 million).

ECKA Restructures Copper Powder Unit ECKA Granulate GmbH & Co. KG, Fuerth, Germany, announced the restructuring of its Red Metal Division. The restructuring includes discontinuing copper powder production at ECKA Granulate MicroMet GmbH at the Norddeutsche Affinerie copper refinery in Hamburg, Germany, by September 30, 2008.

Tungsten Carbide Producer Acquired Ceratizit S.A., Mamer, Luxembourg, acquired privately owned Newcomer Products, Inc., Latrobe, Pa., on July 10. Founded in 1945, Newcomer specializes in manufacturing and finishing tungsten carbide products for metal-cutting and wear applications.

Plant Opening in China Metaldyne, Plymouth, Mich., an Asahi Tec company, opened its first manufacturing plant in Suzhou, China. The 92,000 sq. ft. plant will make crankshaft damper assemblies, knuckle and control arm assemblies, aluminum

Strong Tungsten Sales North American Tungsten Corp. Ltd. (NATC), Vancouver, Canada, reported tungsten concentrate sales of 82,099 metric ton units (MTU) for the quarter ended June 30, 2007, a 14 percent increase over the previous quarter.

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

New Hardfacing Alloy The NanoSteel Company, Providence, R.I., has introduced SHS 9700, a new hardfacing alloy featuring a very fine crystalline microstructure and very high hardness up to 69 Rc, achieved without nickel, molybdenum, or tungsten. The company claims the alloy provides exceptional wear resistance in severe abrasion applications up to five times better than chrome carbide and complex carbide materials. PM Progress at GKN GKN Plc, London, U.K., reported that its powder metallurgy operations made good progress during the first six months of 2007 with higher sales, profits, and margins. The company expects PM to continue improving in the second half. H.C. Starck Sells Unit H.C. Starck GmbH, Goslar, Germany, sold its battery products business to Toda Kogyo Corp., Hiroshima, Japan, for an undisclosed amount. The companies began a business relationship in 2003 when they jointly developed new battery cathode materials.

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Powders

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SPOTLIGHT ON ...

KEN WATSON, PMT Education: BS Mechanical Engineering, Lehigh University, 1996 Why did you study powder metallurgy/particulate materials? I first encountered powder metallurgy (PM) as a part of a materials science class I took when I was in college. I remember thinking that it was an interesting process. The ability to start with a fine metal powder and end up with a metal part that looked and felt solid intrigued me. Understanding the mechanics of alloying and why materials behave the way they do has always been interesting to me. When did your interest in engineering/science begin? I have always been interested in how things worked and in making things, going back to the first time I played with Lego blocks when growing up. The pivotal initiation to engineering and science, however, came from my high school physics teacher. He showed me how mathematics could be used to describe the world around us and predict what might happen. That lesson was very exciting to me. What was your first job in PM? What did you do? I was a manufacturing engineering technician for GKN in St. Marys. This job provided me with an excellent chance to learn the basics of PM while I was working in a capacity for which I was well prepared. Primarily, I worked on tasks such as qualifying new pieces of equipment, small automation projects, and mechanical process improvements. All of these projects touched on the PM process and gave me a chance to “get my feet wet.” Describe your career path, companies worked for, and responsibilities. I accepted an ROTC scholarship, so my first job out of college was as a combat engineer platoon leader in the army. I was responsible for training, vehicle maintenance, and leading a platoon of 28 soldiers. The army was a great place to learn work ethics, time management, and how to make a plan and adjust it. Also, I learned a lot about machines and how they work. When Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

your unit’s ability to do its job rests on the machines that are part of it, a special emphasis is placed on how well the machines are maintained and what can go wrong with them. Plus, as an engineer, nothing is cooler than seeing a 12-cylinder turbocharged diesel tank engine on the floor of the work bay! Upon leaving the army, I found the engineering opportunity with GKN and jumped at it. I was really excited to be able to get involved in PM. After the project engineer position in St. Marys, I had an opportunity to be the process engineer at the GKN facility in Marshall, Illinois. I was the only engineer on site and was responsible both for setting up and controlling the process, as well as responding to customer concerns. Fortunately, I had great mentors there and had a chance to grow in a small facility. Following the closure of the Marshall facility, I continued working for GKN as a process engineer and moved up to Zeeland, Michigan. It is always interesting to see the differences in the ways plants go about their business. We put together a good team in Zeeland, and I will always be proud to have been a part of that. In my last year in Zeeland, I was promoted to product applications engineer. In this role, I had a chance to have much closer contact with the customers' engineers. Seeing all of the applications for PM was a new experience. It was also gratifying to be able to prevent potential problems in the design phase. This past year, I accepted an offer to become the technical service engineer for ACuPowder. Having spent the majority of my PM career working with ferrous metals, it has been exciting to learn the details of powder characteristics and the behavior of compacted bronzes and copper during sintering. It has been enjoyable not only helping customers solve problems, but also helping to improve our products with firsthand knowledge of how they are used. Technical Services Engineer ACuPowder International, LLC 901 Lehigh Avenue Union, New Jersey 07083 [email protected]

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SPOTLIGHT ON ...KEN WATSON, PMT

What gives you the most satisfaction in your career? For me, the greatest satisfaction is in discovery. The process of making and testing an assumption, then interpreting the results to determine if the assumption is correct. Even incorrect assumptions can provide interesting possibilities in the future. List your MPIF/APMI activities. I have taken advantage of the MPIF PM basic and advanced short courses and this year had the opportunity to go to a PowderMet conference for the first time. I learned much from each of these experiences. What major changes/trend(s) in the PM industry have you seen? I believe higher densities and more complex geometries are the wave of the future. Particularly within the automotive market, automakers are trying to save weight but still want the same level of performance they had previously. I believe the challenge will become how to provide these properties and keep the process robust. Why did you choose to pursue PMT certification? When I first started working as a process engineer, I was familiar with the process of making

PM parts but wanted to understand what was occurring in greater detail. I felt that becoming PMT certified would provide the opportunity to learn the science behind the process, and why the process behaves as it does. How have you benefited from PMT certification in your career? Achieving professional certification has benefited me in a number of ways. It has increased my credibility with customers, as they can have more confidence in opinions from someone with professional certification. PMT certification also introduced me to a broad knowledge base, which has been helpful throughout my career. Knowing more about areas of PM technology that I do not encounter on a regular basis has helped me better understand the process of making parts. What are your current interests, hobbies, and activities outside of work? In my spare time I like to go hiking and enjoy the outdoors. As I have recently relocated, I have enjoyed spending more time with my family on the East Coast. Being closer to the football team I supported growing up and finally going to a home game has been a lot of fun. I am also enjoying being near a large city with the cultural attractions that it offers. ijpm

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FURNACES INC. 103 Dewey Street Bloomfield, NJ 07003-4237 Tel: 973-338-6500 Fax: 973-338-1625 Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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CONSULTANTS’ CORNER

OLLE GRINDER* Q

We are trying to optimize our selection of tool materials (i.e., tool steels) and also, to some extent, cemented carbide grades for our powder pressing tooling. Do you have any recommendations on how to choose tool steel grades in order to obtain maximum tool life and minimum tooling costs? It is almost as difficult to choose the right tooling material as it is to design the tooling itself. Selecting suitable tool steels is of the utmost importance. An incorrect choice will inevitably result in premature tool failure due to cracking, chipping or excessive wear. This will directly and significantly increase the tooling costs and also result in higher maintenance costs, higher refurbishment costs, and more down time. The final result is a high production cost per part produced. A number of parameters have a decisive influence on the choice of tooling material. Primarily, these include: • shape of the part to be produced: will the tooling parts have thin sections, chamfers, or sharp corners? • tolerances on the parts produced • number of parts to be produced • compaction pressure • powder grade (e.g., is there a tendency for powder to clad onto the tool material?) • mechanical and functional properties of the tool steel or cemented carbide (e.g., wear resistance, hardness, toughness, and machinability) • material costs The cost of the tooling set with its die, punches, and core rods is, on average, ~5%–10% of the total production cost of sintered steel parts. The cost of the tooling material is often only ~10% of the total tooling cost. The remaining costs are for conventional machining, EDM, heat treatment, etc. It is my firm opinion, after numerous visits to different PM parts producers, that too much focus is being put on the cost of the tooling material instead of on the cost for pressing the part. It is first necessary to consider the different failure mechanisms that are normally encountered in

A

powder pressing before there can be any discussion of the required properties of the tool steel or the cemented carbide to be used. Five main failure mechanisms have been identified for powder pressing tools: • Wear • Chipping • Plastic deformation • Cracking • Galling These mechanisms are of mechanical origin and occur as a result of high stresses, and/or sliding contact between the working surfaces of the tool and the powder. A detailed understanding of these mechanisms, and the relationship between them and tool-steel properties, is critical for selection of the correct tool-steel grade for each application. Wear will always take place on the die, the punches, and the core rods, and is the most common cause for replacement or maintenance. The wear mechanism itself (abrasive, adhesive, or mixed abrasive/adhesive) is difficult to predict. Compaction of powder mixes containing hard particles is likely to give rise primarily to abrasive wear. Adhesive wear dominates when the powder particles are soft, such as in low-carbon steels, austenitic stainless steels, and nonferrous metal powders. These materials tend to “micro weld” to the tool surface. When the welds are broken, small areas of the tool surface can be pulled off and thus cause wear of the surface. Critical tool steel properties for adhesive wear resistance are matrix hardness and ductility. Another important property is the coefficient of friction between the tool and the powder, which is lowered by the lubricants. The level of friction can also be modified by tool surface treatments such as nitriding or surface coatings. Chipping occurs when the stresses on the working surface of the tool are particularly high. The

*PM Technology AB, Global PM Consultants, Drottning Kristinas Vag 48, S-114 28 Stockholm, Sweden; E-mail: grinder@ algonet.se and Associate Professor, Royal Institute of Technology, Stockholm, Sweden

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SHIFT UP TO T110 PM. Today’s part manufacturers require powders with the highest compressibility to achieve the near full densities needed for new automotive gears and sprockets. Inco T110 PM nickel powder offers a performance boost to sintered steels, without the loss in compressibility associated with prealloyed iron powders. Increased diffusion of T110 PM nickel during sintering can double hardenability and significantly improve mechanical properties when compared to standard nickel powder. And with over 100 times as many particles, superior distribution of nickel leads to better part uniformity and greater dimensional precision. At Inco Special Products, we provide nickel solutions for your materials challenges.

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CONSULTANTS’ CORNER

failure mechanism is low-cycle fatigue. It is, therefore, important to make crack initiation and growth more difficult to take place. Using tool steels with a high ductility is the solution to this problem. Plastic defor mation means that the yield strength of the tool has been exceeded. Because yield strength is directly related to hardness, this problem can normally be overcome by increasing the hardness of the tool, taking into consideration the toughness requirements of the tool material. Cracking is also the result of too-high stresses on the tool edges compared with the fatigue strength of the tool steel. Design features causing stress concentrations such as a sharp radius facilitate cracking. The tendency for cracking can be decreased by polishing of the tool surfaces. Galling is closely related to adhesive wear. It usually occurs when working with powders of soft material and results in powder particles “friction welding” to the tool surface—on both punches and dies. A low coefficient of friction between the tool surface and the powder reduces the risk of galling. Recent R&D work has shown that galling is likely to be a more severe problem than was previously thought. It seems that adhesive wear, and frequently abrasive wear, start with cladding (i.e., galling) of powder particles on the tool parts. These clad particles are spalled off and give, by definition, adhesive wear. These spalled particles (debris) become extremely hard due to work hardening and can stick between the moving tool parts and cause abrasive wear. It is also important to remember that premature failure such cracking can be caused by other factors such as misalignment of the moving punches. Failure due to cracking, chipping or plastic deformation, often occurs after pressing only a small number of parts—long before the tool has worn out. It is therefore good practice to try to choose tool steels and hardening conditions so that these premature failures are avoided. The tool life is then limited primarily by wear. Tool steels for powder pressing should thus have: • a high wear resistance • a high galling resistance • a high fatigue resistance • sufficient compressive strength However, there is no tool steel that fully meets these four requirements. This means that a compromise has to be made from case to case. Figure 1 shows impact energy vs. hardness for some common tool steels used in powder pressing punches and often also in dies.1 AISI H13, S7, D2, and M2 are classical cast and forged tool steels which have been used in powder pressing tooling for many years. PM23 is the well-known HSS Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

grade. Uddeholm UNIMAX* and Uddeholm CALDIE* are two highly ductile ESR remelted matrix steels. Uddeholm VANADIS 4 Extra* and Uddeholm VANCRON 40* are PM HIPed and wrought tool steels. Uddeholm WEARTEC SF* is a spray-formed, carbide-rich tool steel. All these steels are produced by Uddeholm Tooling AB. It is evident that the impact energy (which is a good measure of ductility) varies widely from steel to steel and is highest for the matrix steels and Uddeholm VANADIS 4 Extra.* Figure 2 shows abrasive wear resistance vs. hardness.1 Uddeholm WEARTEC SF* has a high abrasive-wear resistance and is thus an interesting alternative to cemented carbides for dies. It is common to use cemented carbides as the tooling material for dies and also sometimes for core rods. This is an appropriate choice under abrasive-wear conditions in long production runs. • Tool steels can be used advantageously: • for short production runs (lower material costs) • to reduce the risk of cladding/galling of powder onto the die surface • to reduce the risk for cracking of geometrically unfavorable carbide dies

Figure 1. Impact energy vs. hardness for unnotched specimens1

Figure 2. Abrasive-wear resistance of tool steels (pin-on-disc test)1

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CONSULTANTS’ CORNER

Q

What can be done to avoid scratches on the surfaces of as-pressed and subsequently on as-sintered parts? The scratches are over almost all of the surfaces and are parallel to the pressing direction. They appear sometimes after only 10–20,000 pressings. This results in an extra cost for maintenance, and also irritates customers. You almost certainly have problems with galling, i.e., cladding of powder particles onto the die surfaces. The tendency for galling can be decreased by polishing the surface and PVD coating the tool part with a hard TiAlN layer. It is, of course, more difficult to PVD coat the die cavity. The galling resistance is somewhat better for PM tool steels compared with conventional (cast and forged) tool steels. High surface hardness and efficient lubrication also have positive effects. Galling results in the following: • a poor surface appearance (scratches) • higher friction between the pressed part and the tooling, resulting in higher ejection forces • the possibility of cracks in the green body, and ultimately • higher ejection forces which result in premature tool failure due to cracking Recently, there has been an interesting development in this field of a new low-friction and antigalling tool steel, Uddeholm VANCRON 40*. This PM steel is now being used successfully in many applications, including powder pressing, to solve galling/cladding problems. Uddeholm VANCRON 40* has a unique chemical composition Fe-1.8 w/o N1.1 w/o C-4.5 w/o Cr-3.2 w/o Mo-3.7 w/o W-8.5 w/o V. The alloying elements nitrogen, carbon, and vanadium combine to form a fine, hard dispersion of vanadium carbonitrides. This steel need not be surface coated. Industrial trials have shown that the ejection force is up to 30% lower for the same part when the tooling is made from this PM steel, instead of conventional PM or cast and forged tool steels.

A

REFERENCE 1. R. Jervis, B. Johansson, L. Jönson and Odd Sandberg, “Properties and Application Experience with New Tool Steels for Powder Pressing Applications”, Advances in Powder Metallurgy & Particulate Materials—2007, compiled by J. Engquist and T.F. Murphy, FAPMI, Metal Powder Industries Federation, Princeton, NJ, 2007, vol. 2, part 7, pp. 106–117. ijpm

*Trade name, Uddeholm Tooling AB.

Readers are invited to send in questions for future issues. Submit your questions to: Consultants’ Corner, APMI International, 105 College Road East, Princeton, NJ 08540-6692; Fax (609) 987-8523; E-mail: [email protected]

14

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Blachford Lubricants the perfect choice for both pressing and sizing

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PM METALLOGRAPHY COMPETITION

WINNING ENTRIES: 2007 APMI INTERNATIONAL PM METALLOGRAPHY COMPETITION, PART I GRAND PRIZE Submitted in the Student Category Sponsored by Buehler Ltd., LECO Corporation, and Struers, Inc. CHANGES IN CARBON CONTENT AND MICROSTRUCTURE OF CARBONYL IRON POWDERS DURING HEATING Bor-Yuan Chen Department of Materials Science & Engineering National Taiwan University Taipei, Taiwan Material: Carbonyl Iron Powder (CIP) Etchant: A mixed solution of 4 v/o Nital and 4 w/o Picral Special techniques: a. Field emission scanning electron microscopy (FE-SEM) b. Carbon analysis for combined dissolved carbon and nondissolved carbon c. X-ray diffraction analysis INTRODUCTION: Carbonyl iron powder (CIP), which is frequently used in the powder injection molding (PIM) process, has a high carbon content and an onion ring structure. During debinding and sintering, the carbon content decreases and grain growth occurs, both of which significantly influence the final mechanical properties of sintered PIM parts. However, there is little direct experimental data reported on the change in carbon content and evolution of the microstructure. Moreover, most carbon analyses reported to date present the total carbon content. The individual amounts of the dissolved carbon and the nondissolved carbon

have rarely been provided. Thus, the first objective of this study was to monitor the evolution of the onion ring structure and its correlation with the changes in carbon content. The second objective was to differentiate the amounts of the nondissolved carbon and the dissolved carbon, which are the main factors in determining the mechanical properties. ONION RING STRUCTURE IN THE AS-RECEIVED CIP: CIP is produced through the chemical decomposition of iron pentacarbonyls based on the following reaction: Fe(CO)5(g) = Fe(s) + 5CO(g) 2CO(g) = C(s) + CO2(g)

[1] [2]

The iron powder obtained in reaction [1] serves as a catalyst for reaction [2] in which carbon is formed and deposited on the iron surface. As the iron surface is covered by the carbon and the CO content diminishes, reaction [1] becomes intense and a fresh iron surface is produced again on top of the carbon surface. As this cycle continues, the alternating carbon and iron layers form an onion ring structure, as shown in Figure 1(a), which is a scanning electron micrograph (SEM) of the CIPS-1641 powder (ISP, Wayne, New Jersey). This powder contains a high level of carbon, usually between 0.7 and 0.9 w/o. But little information is available on whether the carbon is present in the form of carbon soot, dissolved carbon, or Fe-C compounds. As this powder is heated, the carbon reacts with the oxides on the iron powder surfaces and/or with the residual oxygen, water vapor, and hydrogen in the atmosphere. Thus,

Presented at PowderMet2007 in Denver, Colorado. Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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PM METALLOGRAPHY COMPETITION

Figure 1(a). Cross section of as-received CIP, showing onion ring structure

Figure 1(b). Cross section of CIP heated to 300°C, showing that nanoscale Fe3C and Fe2C particles formed and that the number of rings decreased

decarburization occurs and degrades the mechanical properties of the sintered compact. METHODOLOGY: The CIP-S-1641 powder was heated at 10°C/min to 300°, 600°, and 900°C in an atmosphere of N2-15 v/o H2 and then furnace cooled in pure nitrogen. The powder was then mounted using Bakelite, ground, polished, and etched with a mixed solution of 4 v/o Nital and 4 w/o Picral. To prevent the powders from being pulled out of the Bakelite during grinding, short grinding and polishing times were used. Different etching times were also used in order to obtain optimum microstructures, since the structures of the alter-

18

nating layers changed after heating. The etched parts were examined using a field emission scanning electron microscope (FE-SEM). To differentiate the dissolved carbon and the nondissolved carbon, the power input of the carbon analyzer (Horiba, Kyoto, Japan) was adjusted so that the nondissolved carbon could be detected at low power inputs, while the dissolved carbon could be detected at high power inputs, as shown in Figure 2. Three calibrations were performed prior to the testing of the specimens. The first used a mixture of pure iron powder and graphite powder with the known ratio as the standard. The second calibration was performed using a mixture of pure iron powder and carbon soot, which was Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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PM METALLOGRAPHY COMPETITION

Figure 1(c). Cross section of CIP heated to 600°C, showing that microscale Fe3C and Fe2C particles formed and that the onion ring structure disappeared

Figure 1(d). Cross section of CIP heated to 900°C, showing that the particle size of Fe3C and Fe2C decreased and that grain growth occurred inside the particle

collected from the unburnt smoke that was deposited on a glass plate placed above a candle flame. The third calibration used a wrought lowcarbon steel. In order to identify the white layer in the onion ring structure, the as-received powder and those that had been heated to different temperatures were dissolved in HCl, and the residues were examined using X-ray diffraction. RESULTS AND DISCUSSIONS: The typical onion ring structure, as shown in Figure 1(a), consists of alternating layers of pure iron and carbon-containing materials. The average distance between the layers is about 100 nm. Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

The X-ray diffraction pattern, Figure 3, indicates that the carbon-containing layer consists of Fe3C, Fe2C, and free carbon. The iron chlorides resulted from the dissolution of the iron powder in the HCl solution. As the temperature increased to 300°C, the alternating layers became less smooth and particles were formed, as shown in Figure 1(b). The constituents remained the same. As the temperature further increased to 600°C, the ring structure disappeared. The white rings broke into individual Fe3C and Fe2C particles and were dispersed in the iron matrix, as shown in Figure 1(c). When the temperature increased to 900°C, decarburization was severe, and only a small amount of

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Figure 2. Carbon analysis of carbonyl iron powder heated to 300°C, 600°C, and 900°C, showing that the nondissolved carbon is detected at a low power input, while the dissolved carbon is detected at a high power input

TABLE I. CONTENTS OF DISSOLVED CARBON AND FREE CARBON IN CARBONYL IRON POWDER HEATED TO 300°C, 600°C, AND 900°C Sample

Dissolved (w/o)

Nondissolved (w/o)

Total (w/o)

A (as-received) B (300°C) C (600°C) D (900°C)

0.038 0.174 0.033 0.007

0.702 0.560 0.493 0.036

0.740 0.734 0.526 0.043

powder, the power input of the C/S analyzer was adjusted. The total carbon content of the asreceived CIP was measured at 0.740 w/o. This included 0.702 w/o nondissolved carbon and 0.038 w/o dissolved carbon, as shown in Figure 2 and Table I. As the temperature increased, the total amount of carbon decreased. However, the amount of dissolved carbon increased slightly to 0.174 w/o at 300°C and then decreased as the temperature further increased.

Figure 3. X-ray diffraction patterns of residuals after CIP was dissolved in HCl solution, showing that Fe3C, Fe2C, and free carbon were present in the powder.

nanoscale Fe x C y particles were present. With fewer grain boundary pinning dispersoids, grain growth was obvious, as shown in Figure 1(d). To differentiate the form of the carbon in the

20

CONCLUSIONS: The evolution of the onion ring structure and the changes in the carbon content in the carbonyl iron powder were investigated in this study. In the as-received powder, the carbon was present mostly as free carbon, with small amounts of Fe3C and Fe2C, as measured using the self-designed current settings in the C/S analyzer and X-ray diffraction. As the powder was heated in the N2-15 v/o H 2 atmosphere, decarburization occurred. Both the amounts of Fe-C compound and free carbon decreased, and the onion ring structure disappeared at about 600°C. After heating to 900°C, only some nanoscale Fe3C and Fe2C particles were present, and grain growth was obvious. ijpm Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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COPPER PM: NEW DEVELOPMENTS & APPLICATIONS

EXPANDING THE MARKET FOR PM COPPER: BEYOND SELF-LUBRICATING BEARINGS Pierre W. Taubenblat, FASM*

HISTORICAL BACKGROUND When markets are new and there is no competition, early entrants usually establish long-term dominance by focusing on niche applications. The copper powder market relies on a niche application, selflubricating bearings, for more than half of its business. This dependency tends to hinder market growth, especially in North America and Europe. The history of PM is replete with examples of industry pioneers who were early entrants and were successful with a niche application strategy at a time when the market was still in its infancy. Around 1800, William Wollaston developed a process for producing a powder form of platinum. Wollaston kept his process a secret throughout his entire life and succeeded in making over 1,023 kg (2,250 lbs.) of platinum powder for the niche application of a lining for the touch holes of pistols and sporting guns to resist the corrosiveness of gunpowder fumes. He was able to see and discover two additional elements, palladium and rhodium, and made a fortune (over £30,000 at that time) from selling the "malleable" platinum. In the mid-19th century, Henry Bessemer was one of the first engineers/inventors to realize the potential of PM by creating a manufacturing process for bronze powders. This was years before he became more widely recognized for his invention of the Bessemer steel-making process. The idea came to him while helping his sister by applying his skill at calligraphy using a decorative gold colored ink made from a very expensive hand-ground bronze powder. Bessemer, a brilliant engineer, spent the next several years designing a mechanical lathing process for producing the powder, creating steam-powered machines, assembling them in secret from different manufacturers scattered around the country, and, like Wollaston, trusting only a few family members with any information on his process. Also similar to Wollaston, Bessemer made a fortune cornering the market for this decorative-powder niche application.

Since its inception, more than 50% of the copper powder metallurgy (PM) market has been vested in self-lubricating bearings (SLB) as a niche application. This scenario is changing as China’s impact on the market increases. Looking beyond SLBs, an application selection strategy is presented which identifies eight key non-SLB categories for growth: self-lubricating products; projectiles; immiscible systems; building, construction, and joining; coatings, paints, and printing; fungicidal products; electrical/ electronic products; and decorative uses. An exciting future with attendant growth is predicted for the copper PM industry if it is prepared to venture beyond the traditional SLB market.

*President, Promet Associates, 358 North 4th Avenue, Highland Park, New Jersey 08904, USA; E-mail: [email protected]

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EXPANDING THE MARKET FOR PM COPPER: BEYOND SELF-LUBRICATING BEARINGS

Today, we are in vastly different times with a developed copper PM industry, and the environments of Wollaston and Bessemer are, in many ways, polar opposites of the PM industry today. A close look at the worldwide market for copper powder shows that too much focus on a single application could slow the overall health and potential of the industry. Though it is 90 years old and the king of all applications for copper powder, we need to move the emphasis away from SLB as an application. Maintaining SLB growth, while reducing its overall influence (50%–60%) as an application, will allow the copper PM industry to build up and discover other higher-growth applications.

MARKET SIZE In reviewing recent statistics on the size of the global copper powder market, it is apparent that China’s impact on the market has been significant over the last few years. Its overheated economy has produced a large long-term internal demand for copper powder, coming mostly from construction, automotive, and light machinery needs. Unlike Russia, whose growing PM market is fueled by exports, China's exports of PM are more balanced and contribute to, and stabilize, its selfsustaining market. Promet Associates’ projections of the market over the next four years (Table I) continues this trend, predicting that China will nearly double its relative market share, moving

TABLE I. INTERNATIONAL COPPER AND COPPER-BASE POWDER SHIPMENTS

CAGR = Compound annual growth rate: 2006–2010. Totals are in short tons. 1 st = 0.9078 mt Sources: Promet Associates, MPIF, EPMA, JPMA, J. Capus

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EXPANDING THE MARKET FOR PM COPPER: BEYOND SELF-LUBRICATING BEARINGS

from a 17% slice of total copper and copper-base powder shipments in 2006 to 28.4% of the market in 2010. This enormous shift in power and influence overshadows every other sector, even those that are growing. Japan and India, which are predicted to grow over the next four years by 5.6% and 5%, respectively, show the least shift since their own growth counteracts China’s pull and leaves them with about the same slice of market share (about 10% and 7%, respectively) in 2010. A majority of China’s relative market-share gain through 2010 will come at the expense of North America and Western Europe. These two geographic entities will decline in importance from about 25% and 17% of the market in 2006 to about 20% and 13% of the market in 2010. Decreased share, especially when compared with China, does not mean that the overall market is not growing and individual regional markets are decreasing. China’s impact also affects the global market in a positive way and Promet Associates predicts the total global market will grow from 80,431 mt (88,600 st) in 2006 to 101,220 mt (111,500 st) in 2010 or at a healthy 5.9% CAGR. North America and Western Europe will remain essentially flat at 1.0% and -0.7% CAGR from 2006 to 2010. These estimates and predictions assume that the key market application categories remain the same. Currently SLBs account for about 55% of all shipments with other applications making up the remaining 45%. Market forces will drive down

this percentage. Promet Associates looked at this conservative situation over the next four years to 2010 where the ratio of SLB to other applications declines from 55%/45% to 40%/60%. Shown in Table II (Scenario 1), are the non-SLB (other) applications; this sector is growing at a healthy annual rate of 13.7%. Promet Associates also looked at a more aggressive scenario where the market works proactively to focus on, and shift attention to, a key set of eight applications in the other category, while making significant adjustments to the SLB category. In Scenario 2 (Table III), the SLB application declines by 7% per year as the other applications compensate at a growth rate of nearly 21% per year. This high rate of growth completely offsets the decline in SLBs and even catalyzes the entire market so that the global market has expanded and is now growing at 8% per year with approximately 109,000 mt (120,000 st) of copper and copper-base products shipped in 2010. To achieve the ideal outcomes of Scenario 2, Promet Associates examined the eight key applications to focus on how changing the SLB category can help achieve the second more proactive strategy. APPLICATION SELECTION STRATEGY There are many ways to analyze which applications to focus on for a base technology. As an introduction to this Focus Issue of the Journal, Promet Associates concentrated on the union of specific beneficial properties of copper and the

TABLE II. FOUR-YEAR PROJECTION OF SLB AND OTHER APPLICATIONS—SCENARIO 1

SLB Other Applications Total

%

Copper and Copper-Base Powder Shipments mt (st) 2006

CAGR 2006–2010

Copper and Copper-Base Powder Shipments mt (st) 2010

%

55% 45% 100%

44,210 (48,700) 36,221 (39,900) 80, 431 (88,600)

-2.0% 13.7% 5.9%

40,760 (44,900) 60,460 (66,600) 101,220 (111,500)

40% 60% 100%

TABLE III. FOUR-YEAR PROJECTION OF SLB AND OTHER APPLICATIONS—SCENARIO 2 %

SLB Other Applications (1)-(8)* Total

55% 45% 100%

Copper and Copper-Base Powder Shipments mt (st) 2006

CAGR 2006–2010

Copper and Copper-Base Powder Shipments mt (st) 2010

%

44,210 (48,700) 36,221 (39,900) 80,431 (88,600)

-7.2% 20.6% 8.0%

32,820 (36,150) 76,573 (84,350) 109,000 (120,000)

30% 70% 100%

*These eight classes of non-SLB applications are considered in the section titled “Application Selection Strategy.” Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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EXPANDING THE MARKET FOR PM COPPER: BEYOND SELF-LUBRICATING BEARINGS

unique positive aspects of PM. Promet Associates looked at many specific niche applications ranging from brass saxophone keys to poker chips and came up with the following eight broader classes of applications that will drive copper PM’s growth over the next four years: (1) Self-Lubricating Products To retain the competitiveness of self-lubricating bearings as a key application, the approach should be modified and the category enlarged to include not only bearings but also other products that can leverage the unique properties of the material. As a starting point, there is ample opportunity to enlarge the market by improving the life of existing products by increasing the hours of continuous operation. In his article "Copper-Base PM: Past, Present, & Future," William Ulrich, ACuPowder International, LLC, cites the possibility of increasing the strength of bronze to create increased durability for SLBs and other applications. These same attributes can enlarge the category to include any parts that involve friction, especially between two metal surfaces. For example, there is no reason why moving door components could not be constructed out of a similar material so that it responds to a self-lubricating treatment. (2) Projectiles: Shaped Charges/Frangible Bullets For many years one of the more effective hightechnology anti-tank weapons has been the shaped charge warhead. Because of its unique shape and chemistry it achieves high explosive focusing power and the ability to penetrate metal and armor. While the military uses a variety of metals in different forms for weaponry, such as aluminum to penetrate concrete, the largest user of metal powder for shaped charges has been the petroleum industry. Shaped charges are employed to penetrate the casing of wells to begin a new oil source or later on to admit the influx of more oil. Because the typical shaped charge metal slug that is ejected could plug up the well instead of beginning its operation, metal powders are used which will not create a plug. Pure metal powders with high ductility, such as copper, are preferred because they postpone the breakup of a powerful jet that achieves most of the destructive power.

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Copper powder with a high green strength is also an ideal product for companies like Occidental who use this technology because it yields preferable jets composed of powders in the charge. Similarly, frangible bullets or those that disintegrate upon impact are being manufactured from powders with high green strength. This product is primarily being used in training exercises, firing ranges, and other situations where ricocheting is of concern. The high green strength of certain copper powders is also an advantage here. Though other materials like tin/tungsten alloys are used, they do not have the simplicity of high green strength copper which allows the bullets to be manufactured by pressing through mechanical interlocking or “cold welding.” Promet Associates also sees copper powder’s potential here over the next few years as a replacement for many of these products that are lead based. Organizations such as Oak Ridge National Laboratory are working to substitute materials like copper powder for existing lead-based frangible bullets. (3) Immiscible Systems PM is one of the best ways to produce fully dense high-strength systems consisting of two or more metals/components that cannot be alloyed by conventional processing. New systems similar to Cu-W or dispersion strengthened Cu-Al2O3 can be tailored for applications like welding electrodes, taking advantage of the properties of copper and the admixed component which is transformed after extrusion into fully dense rod or other desired shapes. Many more similar types of systems are possible and should be explored in this high-potential application. (4) Building, Construction, and Joining This application sector benefits from the strong involvement of copper in new home construction, mostly because of wiring. Copper powder is also used for other applications in homes and offices. Lock components and special pipe-joint compounds often have a high copper content and are readily fabricated via PM. Brazing compounds also constitute a significant application for copper powder. The possibility of manufacturing inexpensive standard copper pipe fittings like elbows via PM is being explored in low-cost environments, for example, China. This might also make sense in the U.S. In the industrial market, copper powder is still being Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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tested for different welding processes and nonsparking tools via dispersion-strengthened copper powders and other specialized high-strength copper powders. (5) Coatings, Paints, and Printing While antifouling paints for ships have longterm environmental concerns, other products are being developed to address this concern. As Bessemer recognized 150 years ago, there is usually a strong market for aesthetic decorative products. Metallic printing is increasingly a popular choice for marketing collateral and other business applications. Metallic paint remains a large consumer market. High-end automotive paint is also expanding as metallic colors like "opalescent silver" continue to be in style and copper-colored vehicles become more popular. Fukuda Metal Foil & Powder Co. Ltd., Japan, has been involved for several years in developing an electromagnetic shielding paint made with copper powder. Though stricter regulations have shifted in favor of silver powder, Fukuda has taken its original product and adapted it for wiring printed-circuit boards and in heat-dissipation applications. (6) Fungicidal Products This group of applications takes advantage of copper’s strong antibacterial abilities. In agriculture, work is in progress on using an effective copper-powder-based fungicide for trees, shrubs, fruits, and vegetables. It is also worth exploring whether copper powder might be used to prevent the buildup of mold in homes (roof shingles) and in health-industry environments. Hospitals have for years used bronze door knobs for their germ killing effects. There is room for more antibacterial applications in hospitals and in similar situations. Promet Associates has begun to examine the possibility of creating a special spray, similar to Lysol, with copper powder that will be tested rigorously for eventual use at home and in hospitals and doctor’s offices. (7) Electrical/Electronic Products This class of applications has been receiving the most attention for powder metal possibilities and is growing faster than any other category. Randall German contributes an article to this Focus Issue which examines the MIM process for copper and copper alloys and new applications Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

this PM manufacturing technique offers. A majority of innovative MIM products are being introduced in this application category because of their complexity, small scale, and heat-dissipation capability. A major area that is starting to receive attention is PM heat sinks. Requiring high thermal conductivity and large surface areas for dissipating heat in a tiny footprint, they are ideally suited to copper powder. Also driving the momentum in this category is the increased trend towards miniaturization, heralded most recently by the introduction of the MacMini and iPod. There are other new electronic devices that might have a close fit with copper PM. In June 2007, MIT announced that it could transfer electricity wirelessly. The new system uses copper coil antennas. Though it is uncertain whether PM could be useful here, it is definitely worth testing it as a potential high-level PM application. John Shields’ article “Copper Powder in Electronic Applications” reminds us not to forget other alloys when looking at heat-sink applications. He cites copper/tungsten and copper/ graphite as lightweight alternatives. As the market for traditional products in this class (e.g., PCBs) grows, new markets from discoveries at MIT and elsewhere will expand the potential of this sector for copper-base PM. (8) Decorative Uses Walking down Madison Avenue in New York City it is impossible for a metallurgist not to notice the $40,000 enamel La Cornue stove in Williams-Sonoma’s window. It is replete with solid copper fittings (some could be made through PM) and covered with solid copper pots and pans. One cannot go into a high-end hardware store like Gracious Home and not notice the woman ahead in line purchasing bronze kitchen-sink hardware for $764.00. Copper on its own, or alloyed as bronze, can be an extraordinarily beautiful material. From a marketing perspective this carries with it the promise of larger margins since people are always willing to pay more for beauty. This sector involves some new form factors and offers almost unlimited room for new applications. Research is being carried out on copper foam and other ultra-light materials that might have both practical and decorative use. Another similar example is our conception of creating a new type of metallic thread by embedding copper powder

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particles in individual strands of synthetic fabric such as polyester. This could be used in high-end fashion or woven into special fabrics. Promet Associates has also seen more interest in copper powder added as fillers to polymers to increase strength and thermal or electrical conductivity, and endow them with other attributes such as magnetic properties. Most tourists and visitors to New York City are primarily aware of the symbolic power of the Statue of Liberty as an icon of freedom. It is also the largest copper structure ever created—28 mt (31 st). Passing by the statute, especially from the water, one can see that its majesty also comes from the beautiful green copper patina. In thinking about new applications, it is now possible to prepatinate or artificially coat the green patina normally built up over years. This could also be done with copper powder for decorative or other purposes. Through effective marketing, new copper-powder applications can be found in this sector that not only have practi-

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cal use but also emphasize the inherent beauty of the material. FINAL THOUGHTS It is often easier to stay with the familiar than to change. Copper PM companies need to expand from the familiar 90-year-old SLB applications, to think about changing the parameters to self-lubricating products, and to include other potential self-lubricating applications. The advantages of copper, coupled with the uniqueness of the PM process, need to be promoted in the applications discussed here. The industry has an exciting future. Our forecast shows a nearly 6% yearly increase for total global copper powder over the next four years. By focusing on the applications cited, metal powder companies can proactively adjust their product mix and make a difference in how their challenging markets will grow. ijpm

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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NEXT JUNE THE PM WORLD CONVENES IN WASHINGTON, D.C. 2008 World Congress on Powder Metallurgy & Particulate Materials June 8–12, Washington, D.C. • International Technical Program • Worldwide Trade Exhibition • Special Events

This global PM event is sponsored by:

METAL POWDER INDUSTRIES FEDERATION APMI INTERNATIONAL 105 College Road East Princeton, New Jersey 08540 USA Tel: 609-452-7700 Fax: 609-987-8523 www.mpif.org

In cooperation with: GAYLORD NATIONAL RESORT & CONVENTION CENTER National Harbor on the Potomac

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SCM's products include: • • • • • • •

North Carolina USA

Manufacturing Sites • Research Triangle Park, North Carolina USA • Suzhou, China Tel: 919-544-8090 • www.SCMmetals.com

Copper, Tin and Bronze Premix Powders Prealloyed Bronze and Brass Powders Copper Base Infiltrating Powders High Green Strength Copper Powders Copper Oxides Copper Base Catalyst Powders Cubond® Furnace Brazing Pastes

Suzhou China

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COPPER PM: NEW DEVELOPMENTS & APPLICATIONS

ELECTRONIC APPLICATIONS FOR COPPER POWDER John A. Shields, Jr.* and Ivi Smid**

INTRODUCTION The electronics industry uses copper powder in thermal management (TM) components, usually in the for m of copper–tungsten or copper–molybdenum heat sinks. As solid-state devices become smaller and smaller, power densities increase, creating a need for TM materials that can handle increasing amounts of heat. Other advanced copperbased materials such as copper–graphite and copper–diamond have the potential to improve thermal conductivity (TC) while providing a material compatible with the thermal expansion (TE) of electronic devices. Concurrently, a number of interesting copper-based materials have appeared that offer increased performance of the electronic devices per se. They rely on PM technologies to create and maintain the microstructural characteristics that control performance. These copper “alloys” containing small amounts of tungsten, molybdenum, or other metals added as dispersed phases, are consolidated into sputtering targets, and deposited on silicon devices in the form of thin-film circuitry. As a group, these new materials have the potential to reduce complexity in manufacturing processes, improve process yields, and improve device performance compared with current technology. This paper reviews traditional copper–tungsten and copper–molybdenum heat sink materials, and discusses the state of the art of emerging TM particulate composite materials including copper– graphite and copper–diamond. An overview is also given of emerging copper alloys that show promise in thin-film circuit technology. TRADITIONAL TM MATERIALS: COPPER–TUNGSTEN AND COPPER–MOLYBDENUM Processing and Thermal Properties Pure molybdenum and tungsten metals have long been used to manage heat produced in silicon power devices, because they have a low coefficient of thermal expansion (CTE) and reasonably good electrical conductivity (EC) and TC. Their low CTE minimizes thermal stresses due to an improved TE match between silicon semiconductors and the refractory metal substrate. Their TC, while not as high as that of copper or aluminum, is much better than that of many other metals, so they

Copper powder metallurgy (PM) plays an important role in electronics, as a critical component in thermal management materials; primary examples are copper–tungsten and copper–molybdenum. The requirement for continuing increases in thermal conductivity, without sacrificing thermal expansion compatibility with solid-state devices and packaging substrates, has generated a growing interest in other copper composites utilizing graphite and diamond. These technologies are the focus of extensive R&D and, in some cases, have found commercial application. They offer promise for continuing progress in circuit miniaturization, permitted by higherefficiency thermalmanagement materials. Copper PM technology is also a key component of a new copper-based material aimed at replacing aluminum–neodymium wiring on solid-state devices and thin-film transistor flat-panel display screens. Significant process economies appear to be possible with this material, and raw material pricing pressure on traditional materials may provide an even greater impetus for its adoption.

*Principal, Mill Creek Materials Consulting, 4457 Brooks Road, Cleveland, Ohio 44105-6053, USA; E-mail: [email protected], **Associate Professor, Center for Innovative Sintered Products, The Pennsylvania State University, 147 Research West, University Park, Pennsylvania 16802-6809, USA; E-mail: [email protected]

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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can remove heat from devices efficiently. This further reduces thermal stresses and keeps operating temperatures low. Low stresses and low temperatures substantially extend the operating life of silicon semiconductors. Modern integrated circuits require TM materials with different characteristics than the molybdenum and tungsten substrates traditionally used for silicon devices. Integrated circuits are typically mounted on brittle ceramic substrates that have CTE values higher than that of silicon, but much lower than that of high TC metals such as copper and aluminum. To meet the need for heat sinks with higher CTEs, tungsten and molybdenum are utilized as constituents in composite materials that take advantage of copper’s higher CTE and excellent EC and TC. Creating the copper–refractory metal composite boosts the TC of the composite above that of the pure refractory metal, and allows designers to tailor the TE of the composite by controlling the volume fraction of the copper. Expansion matches are thus possible with materials for which the pure refractory metal would be too low, and pure copper would be too high. Table I summarizes the thermal properties of selected materials used in integrated circuit technology.1–9 The composites in this table can have a wide range of values depending upon the specific properties of the individual components, the method of manufacture, and the phase fractions in the composite. The data show that in order to provide good expansion matching between the ceramic substrates commonly used in integrated circuit technology, new materials are required. Composite materials are the solution, and several materials are now available in the marketplace, each with its own advantages and disadvantages. Clad sheet products such as copper–molybdenum–copper or copper–Invar™–copper have anisotropic properties, and cannot be readily fabricated into multilevel configurations without creating thermal bowing and dimensional stability problems. Particulate composites can solve the problem of isotropy, but each approach presents different challenges. Aluminum–silicon carbide is difficult to machine because it contains a high-volume fraction of silicon carbide. Typically, it is used where large runs of product can amortize the cost of tooling for net-shape processing. Its property range is relatively narrow, constrained by the volume fraction of carbide that can be distributed uniformly in the aluminum

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matrix. Aluminum–graphite composites are capable of providing a wider range of properties, but have not seen significant use because of manufacturing issues that remain to be solved. Copper– tungsten and copper–molybdenum composites, though they are relatively expensive materials due to the refractory metal content, and they impose some weight penalties, remain the primary solutions to the problems of TM for integrated devices. They have a wide range of properties that can be readily controlled by selecting an appropriate composition and are compatible with existing PM manufacturing processes. They can be machined from monolithic forms, pressed and sintered to shape, or injection molded to near-net shape. Sumitomo Electric Industries defined the use of copper–tungsten and copper–molybdenum heat sinks with controlled TE properties. 2–5 Their patents identified a range of compositions from 1 w/o copper in molybdenum or tungsten, to as high as 40 w/o copper in tungsten or 50 w/o copper in molybdenum. The early patents covered substrates made in two ways. In one manufacturing approach, presintered compacts of molybdenum or tungsten with controlled amounts of interconnected porosity, were infiltrated with molten copper. A second approach blended, TABLE I. REPRESENTATIVE THERMAL PROPERTIES OF MATERIALS USED IN SOLID-STATE DEVICES Material

CTE at 298 K (10-6/K)

Thermal Conductivity (W/m·K)

Si GaAs Al2O3 BeO AlN SiC Mo W C (diamond) C (pitch fiber) C (pyrolytic graphite) Cu-W Cu-Mo AlSiC Cu-Graphite Cu-Diamond Al-Graphite Cu-Mo-Cu Cu-Invar-Cu

2.8–4.2 5.9 6.7 8.0 4.5 2.8–4.9 5.0 4.5 1.7 -1.6a/-0.9b 27a/-0.5c 4.7–11.8 5.3–11.5 6.5–13.5 7c/16d 4–6 4–7c/24d 5.5–8.8c 5.2c

150 46 21 275 250 80–490 140 168 2,000 1,100a/5b 10a/2,000c 167–305 146–276 170–220 275–300c/220–230d 600 200–230c/120–125d 166–305c/152–249d 167c

aaxial, btransverse, cin-plane, dthrough-thickness

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pressed, and liquid-phase-sintered copper and either molybdenum or tungsten powders. Molybdenum and tungsten have no mutual solubility with copper at the temperatures used to process the composite material10,11 so interdiffusion and mutual contamination do not occur. This is a key factor in the success of the approach, because minor alloy constituents can have a strong negative effect on TC.12,13 The two manufacturing approaches do not produce the same product from the standpoint of thermal properties. Figure 1 shows that, at any given copper content, the CTE of tungsten composites made from liquid-phase-sintered powder blends is higher than that of infiltrated compacts. Figure 3. Correlation between TC and CTE for infiltrated and blended, and liquidphase-sintered copper–tungsten composites

Figure 1. CTE of infiltrated copper–tungsten compared with that of blended and liquid-phase-sintered copper–tungsten, as a function of copper content

Figure 2. TC of infiltrated copper–tungsten compared with that of blended and liquid-phase-sintered copper–tungsten, as a function of copper content

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

Figure 2 shows that, at a given volume fraction of copper, liquid-phase-sintered powder blends have a lower TC than infiltrated compacts. Since the purpose of these materials is to lower CTE with minimal effect on TC, infiltration is the preferred processing route. Figure 3 combines the data to better illustrate this conclusion. In this figure, the TC of each composition is plotted as a function of its TE. At any specified/required level of TE, the infiltrated material has a 25 to 40 W/m·K TC advantage over the liquid-phase-sintered material. At any specified/required TC, the CTE of the infiltrated material is 1–2 ppm/K lower than that of the liquid-phase-sintered material. These disparities are smaller at lower copper contents, but the infiltrated material clearly provides an enhanced combination of CTE and TC compared with pressed-and-sintered powder blends at all copper contents. At lower copper contents, the values of TC and CTE tend toward those of pure tungsten, and the difference between the two consolidation approaches diminishes. For copper levels in the range 10–15 v/o, this difference may well be of the same magnitude as the process variability. Figure 4 14 illustrates typical heat sinks and devices used in telecommunications equipment such as cellular telephone base stations. Copper–tungsten heat sinks are widely used in this application, where performance is the primary driving force and weight is not a major concern. Here the high density of tungsten can be accepted. Figures 5 and 6 compare CTE and TC, respec-

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Figure 4. Representative copper–tungsten products used in telecommunications TM applications.14 Courtesy PLANSEE Metall GmbH

Figure 6. TC of presintered-and-infiltrated copper–tungsten and copper– molybdenum composites as a function of copper content

tively, of infiltrated copper–tungsten with those of infiltrated copper–molybdenum, again using data from the Sumitomo patents. Figure 7 combines the data into a single graph showing that copper–tungsten has a clear performance advantage. At any CTE value, copper–tungsten has a TC advantage of 30–35 W/m·K over copper–molybdenum. For a given TC, its CTE is ~2 ppm/K lower than that of copper–molybdenum. Despite the lower performance compared with copper–tungsten, copper–molybdenum heat sinks are used in the automotive industry in power control modules for hybrid vehicles, Figure 8.14 These modules use much larger heat sinks than telecommunications devices. Power component weight affects overall

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Figure 5. CTE of presintered-and-infiltrated copper–tungsten and copper– molybdenum composites as a function of copper content

Figure 7. Correlation between TC and CTE for presintered-and-infiltrated copper– tungsten and copper–molybdenum composites

vehicle efficiency, so copper–molybdenum is preferred over copper–tungsten in this application. Copper–molybdenum is also more machinable and formable than copper–tungsten which makes it desirable from a manufacturing standpoint. Though the density of copper–molybdenum is lower than that of copper–tungsten, it still faces tough competition from other composite materials such as aluminum–silicon carbide, which can provide additional weight savings. Powder and Process Development Even though infiltrated composites have a preferred combination of CTE and TC, effort has been devoted to material and process development utiVolume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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copper–carbon adhesion and its impact on heat transfer across the copper–carbon interfaces, less-than-ideal dispersion of the carbon filler particles, and difficult-to-machine copper–diamond composites. Commercial applications in high-performance TM components can be expected within several years as these problems are solved.

Figure 8. Copper–molybdenum baseplate used in mobile power conversion applications.14 Courtesy PLANSEE Metall GmbH

lizing blended powders. Most copper–tungsten applications are in the range of 10–20 v/o tungsten, where the penalty in thermal properties for using a pressed-and-sintered powder blend is acceptable. Pressing and sintering, and powder injection molding (PIM), offer savings in manufacturing and material costs compared with infiltrating presintered preforms. Investigators have taken a variety of approaches to preparing powders that produce high-density pressed-and-sintered composites. Spray drying, 15 ball milling, 16,17 and mechanical alloying,17 have been examined as ways to create powders having good flowability and sinterability. Copper-coated powders18 and copper-cored powders19–22 have also been investigated as ways to simplify consolidation, increase component homogeneity, and to improve sintering behavior. These composite powders are available commercially. The effect of nanoscale powders on ther mal properties has also received attention.13,18 Even spray deposition has been examined as a technology to create these composites. 23 Successful powder development must result in powder that is compatible with standard pressing, sintering, or PIM processes, that will sinter to high density, and that does not suffer from extrinsic contamination. EMERGING TM MATERIALS: COPPER–CARBON Of all the fillers in copper metal matrix composites (MMC), high TC carbonaceous particles show the most promise in combination with the lowest CTE and density. The primary issues are poor Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

Interface Adhesion and Thermal Barrier A carbon filler is the most promising option to reduce the TE of a copper matrix significantly, and at the same time increase the TC. Zweben has published comprehensive reviews.24–26 For electronic packaging, the thermal and physical properties of copper–carbon composites predicted from theory offer potential, especially if highly conductive fillers such as diamond, PITCH fibers, flakes, carbon nanotubes, or nanofibers can be used. The desired balance of low CTE and high TC is illustrated in Figure 9.27 Compared with the properties achieved in copper–tungsten composites, an approximate doubling of the TC is envisaged (Figure 3). However, the gap between the predicted (theory) and the experimentally measured values is significant. In particular, the measured (experimental) TC is 20%–25% lower than predicted. The reason for this gap is the weak interface between the copper matrix and the carbon particles,28 as illustrated by the scanning electron microscope (SEM) image in Figure 10. Any interface results in an interfacial thermal barrier. Even a perfectly bonded interface creates elastic discontinuities which can act as scatterers of phonons. Mismatches in dielectric constants

Figure 9. Balance of CTE and TC in copper–carbon composites.27 Shaded region is the goal

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Figure 10. Weak interface between copper and carbon fibers. Carbon fiber dia. ~10 µm. SEM

further promote phonon scattering. Localized atomic disorder can lead to enhanced phonon and electron scattering. Interdiffusion across the interface can result in solid-solution formation, with TC values well below those of the constituents. Lattice distortions, at or near the interface, due to internal stresses resulting from thermal mismatches, constitute crystal imperfections that can act as electron and phonon scatterers. Interfacial separation as the result of internal stresses can lead to the formation of an interfacial gap; this can extend in part around the interface. Such a gap would represent a significant thermal barrier as it permits interfacial heat transfer by radiation and/or gaseous conduction only. Thus, the existence of an interface with perfect thermal contact appears unlikely.28 This issue has been addressed extensively in the literature.29,30 The Hasselman model29 gives a practical relation for TC:

(1)

where λc is the TC of the composite material, λm is the TC of the matrix, λi is the TC of the spherical inclusions, Vi is the volume fraction of the inclusions, ri is the radius of the inclusions, and Rth is the thermal contact resistance (TCR). Based on

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Figure 11. Predicted influence of TCR on TC of a copper–matrix composite with inclusions of high and low TC28

this formula, the TC of carbon-based metal matrix composites with 40 v/o of 10 µm filler particles has been calculated for different filler particle TCs, Figure 11.28 Further, larger filler particles give a higher composite TC. In contrast to graphite, the heat flow across diamond–metal inter faces changes from phonon transport to electron transport, which further impacts thermal contact and composite TC.31 There is evidence that interface doping can affect this transition.30,31 Alloying Additions to Copper Matrix The primary mode of failure in microelectronic circuits is thermal fatigue. A high-quality copper–carbon interface is essential for durability and fatigue resistance.32 To overcome poor wettability and adhesion between copper and carbonaceous materials a carbide-forming element can be added, with the consequence of reduced heat conduction in the metal matrix. Figure 12 illustrates the effect of alloying on the TC of pure copper. The effect of different alloying elements and their influence on the contact angle to improve the wetting behavior, have been evaluated.33–35 Based on this knowledge, alloying elements such as chromium,36,37 titanium,38 or silicon–chromium alloys39 were used to enhance wettability during liquidphase production of copper–carbon composites. These attempts were partially successful. However, the introduction of alloying elements during liquid-phase production was related to (a) Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Figure 12. Influence of alloying elements on TC of copper. The plot on the right is an expanded view of the boxed region on the left. As an example, 0.8 w/o titanium causes a reduction in TC of 50%

Figure 13. Increase in wettability at copper–diamond interface: (a) uncoated 3 µm dia. diamond particles in 300 nm dia. copper after 1 h at 800°C—particles uncovered; (b) as in (a) but with a 5 nm layer of titanium on diamond particles— particles remain covered. AFM

a reaction layer, which formed at the interface, and (b) a potential decrease in TC. The increase in wettability of diamond in copper, as a result of coating the particles with a thin layer of titanium, is illustrated in Figure 13, utilizing an atomic force microscope (AFM). Recently a bulk TC of up to 600 W/m·K has been reported for copper–diamond metal matrix composites with controlled chromium carbide formation at the interface.31 Extensive R&D activities are ongoing in this field, and commercial applications are to be expected within several years. Fabrication and Machinability of Copper MMCs with Carbon Filler The simple mixing of diamond or carbon fibers with copper followed by hot consolidation, (e.g., hot pressing), is the most economical processing path. Two main problems are the inhomogeneous dispersion of the carbon particles in the copper Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

matrix, and the weak interface between the copper matrix and the carbon filler. The first entity results in filler -to-filler contacts and, in the absence of a continuous copper network, a significant reduction in TC. The second entity is responsible for a weak thermal performance during thermal cycling, as well as a reduction of the achievable TCs.40 Alloying carbide-forming elements in the copper matrix can improve adhesion, but the TC is reduced. In order to maintain the highest possible TC in the copper matrix, localized carbide formation must be limited to a thin layer adjacent to the copper–carbon interface.41 Filler particles have been precoated with a carbide-forming element via sputtering/physical vapor deposition (PVD) or chemical vapor deposition (CVD), or simply mixed with a prealloyed copper powder, and subsequently hot pressed.42,43 A representative microstructure of chromium sputter-coated, chopped carbon

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fibers in pure copper powder after hot pressing is shown in Figure 14. Of all the possible carbon fillers, diamond particles are the most desirable for their high and isotropic TC. Large filler particles (>100 µm dia.) suffer the least degradation in TC induced by TCR. However, there is a dilemma with the machining of copper–diamond MMCs. Mechanical cutting is cumbersome due to the embedded large diamond particles. MMCs with finer diamond particles can be machined to the desired surface smoothness but have a lower TC than pure copper. Alternative ways of machining, such as EDMing, laser sectioning, and water-jet sectioning are being investigated. Other potential carbon fillers are nanofibers and nanotubes. Like diamond, they exhibit TCs ≥1,500 W/m·K. Once successfully dispersed and aligned in a copper matrix, and keeping the TCR low, these composites are expected to exhibit promising (anisotropic) properties. In contrast to copper–diamond, nanofiber and nanotube copper composites are relatively easy to machine. It is interesting to note that, as carbon nanotube production is becoming more economical, space applications (another demanding high-performance field) are promoting interest in the development of copper-base MMCs.44

Figure 14. Hot-pressed chromium sputter-coated, chopped carbon fibers in pure copper powder.10 SEM

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COPPER PM FOR MICROELECTRONIC APPLICATIONS Flat-panel display (FPD) sales have skyrocketed in recent years, due to the availability of increasingly large screens at continuously decreasing prices. Thin-film transistor (TFT) liquid-crystal display (LCD) technology has a dominant position in the market for smaller displays, and is now challenging plasma displays for large screen applications. Manufacturers of these displays use many of the traditional PVD processes developed for silicon, but the size of glass panels has driven advances in the size of equipment and sputtering targets used to coat the glass. Current technology uses aluminum–neodymium circuitry sputtered on glass substrates as part of the process to build circuits and transistors for the panels. Larger screens mean longer delay times in signal transmission from point to point, creating problems with image quality. Manufacturers are designing displays that employ copper circuitry, which will significantly increase switching speeds and allow for continued growth in screen size. Both the aluminum–neodymium circuits and copper circuits now require protective layers beneath and above them. Molybdenum is used as a base for aluminum–neodymium because it bonds well to glass, and provides protection of the aluminum circuit from the process environments present in manufacturing. Copper circuits are not compatible with molybdenum as aluminum, and typically require molybdenum– titanium or molybdenum–niobium both as a substrate and an overcoat. Copper circuits on silicon devices normally use tantalum as diffusion barriers to prevent the formation of copper silicides and contamination of the silicon device with copper. In all these cases, the need to deposit a substrate as well as a protective coating means additional processing steps. Every additional step brings with it yield losses, manufacturing cost increases, and throughput issues. A copper -base material, “high-performance copper” (HPC), has been developed45 that has the potential to eliminate the substrate deposition and circuit-coating steps, allowing placement of the copper wiring directly on the screen or device. Figure 15 illustrates a typical gate structure using aluminum–neodymium, and compares it with the same structure using this new copper-base material. 46 Replacing the molybdenum/aluminum– neodymium/molybdenum layers with a single Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Figure 15. Schematic illustrating the effect of replacing traditional molybdenum–aluminum/neodymium–molybdenum wiring (left) with HPC wiring (right). Note the reduction in layers deposited using HPC.

copper alloy layer reduces the number of steps required to manufacture the populated screen from ten to seven.46 HPC is particularly interesting to PM technologists because it requires PM to consolidate the targets. Copper powder is blended with molybdenum powder at molybdenum contents of a few w/o. The powder blend is pressed and sintered in order to produce sputtering targets. Because copper and molybdenum are not mutually soluble, they are present in the target as pure elemental phases. Sputtering mixes the two materials uniformly in the sputtered circuitry, where the molybdenum migrates to grain boundaries in the sputtered film during processing. Investigators believe that it provides barriers to grain boundary diffusion of silicon in the copper, thus eliminating the formation of copper silicides at normal processing and operating temperatures. Figure 1646

Figure 16. X-ray diffraction patterns of sputtered films of copper and HPC on silicon4,5

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

compares the X-ray diffraction spectrum of HPC on silicon in the as-deposited state with the spectrum from the alloy and pure copper after a 400°C anneal. Significant formation of copper silicide occurs in the pure copper deposit during annealing, reducing circuit performance. The alloy is not completely resistant to silicide formation, but the onset of silicide formation is raised by nearly 100°C compared to pure copper. This is more than sufficient to render the alloy stable with respect to processing and operating conditions. The developer of HPC claims a number of advantages over current aluminum–neodymium technology, including improved yields, lower direct process costs, lower electrical resistivity, capability of finer-pitch wiring, elimination of chromium in devices that use it as a diffusion barrier, high adhesion, good etchability in standard process environments, and enhanced oxidation resistance compared with pure copper. It is not clear whether this material will be accepted in the marketplace; if it is, the potential is large. Using molybdenum as a measure of the overall market potential is one way to estimate the potential consumption of the material. One estimate of the 2005 molybdenum powder demand to support FPD manufacturing is ~2,000 mt. 47 Demand at that time was still growing rather dramatically, and even today continues on a steady increase, though at lower growth rates. It is unlikely that all of the molybdenum demand will be replaced by this new material, but the number serves as a reference point for the opportunity that is available. Figure 17 illustrates why this material could be of significant interest independent from any process efficiencies it can generate; it summarizes recent molybdenum price history.48 The price of molybdenum, like that of other met-

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Figure 17. History of molybdenum pricing48

als used in capital equipment, has increased dramatically in the last few years. Currently, molybdenum is trading near $80–$85/kg. Expectations are that it will remain in this range for the near future as the economies of China and India grow at healthy rates. Copper, while also subject to significant price increases in recent years, trades at a fraction of the price of molybdenum, so substantial cost savings in material alone can be captured if the technology is successful. SUMMARY Both liquid-phase-sintered and presinteredand-infiltrated approaches are used to fabricate copper–tungsten and copper–molybdenum heat sinks. Comparing manufacturing routes reveals: • Infiltrated composites have a TC advantage over liquid-phase-sintered composites at any target value of CTE, and a CTE advantage at any value of TC. • Copper–tungsten has a TC advantage over copper–molybdenum at any target value of CTE, and a CTE advantage at any value of TC. • At low copper contents, the small difference in properties between infiltrated and liquidphase-sintered composites is acceptable for components that are candidates for near-netshape forming. This drives significant R&D work to optimize powders and processes for liquid-phase-sintered materials. The requirement for continuing increases in TC without sacrificing thermal expansion compatibility with solid-state devices and packaging substrates, has generated interest in other

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copper-base composites with graphite and diamond. The problems to be solved in copper–carbon composites, and some of their promising solutions, include: • Poor particle–matrix bond strength: matrix alloying, and fibers coated with reactive metals such as chromium or titanium, show promise in improving interfacial bonding. • Detrimental effects of alloying on matrix TC, but composites of copper and chromiumcoated diamond have shown promise, exhibiting TC values as high as 600 W/m·K. • Machinability and fabricability of diamond composites: these problems are being attacked with machining technologies that do not require mechanical interaction between tool and workpiece, e.g., laser and EDM machining, and the use of net-shape-forming technologies. A new copper PM technology shows promise in the manufacture of solid-state devices and TFTFPD screens. It employs sputtering targets of copper–refractory metal alloy (molybdenum, tungsten, tantalum) that produce circuit lines free from copper silicide formation under standard processing and operating temperatures. Developers cite several advantages of the material, including: • Improved process yields due to fewer processing steps • Lower direct processing costs due to fewer processing steps • Lower electrical resistance of sputtered films, allowing faster response times and enabling large displays • Finer-pitch wiring than standard aluminumneodymium wiring • Elimination of chromium in devices using it as a diffusion barrier, and • Enhanced oxidation resistance compared with pure copper REFERENCES 1. S. Jin, “Advances in Thermal Management Materials for Electronic Applications”, JOM, 1998, vol. 50, no. 6, p. 46. 2. A. Sasami, H. Sakanoue, M. Miyaka and A. Yamakawa, “Member for a Semiconductor Structure”, U.S. Patent No. 4,965,659, October 23, 1990. 3. M. Osada, Y. Amano, N. Ogasa and A. Ohtsuka, “Substrate for Semiconducting Apparatus Having a Composite Material”, U.S. Patent No. 5,086,333, February 4, 1992. 4. M. Osada, Y. Amano, N. Ogasa and A. Ohtsuka, “Substrate for Semiconductor Apparatus”, U.S. Patent No.

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5,099,310, February 4, 1992. 5. M. Osada, Y. Amano, N. Ogasa and A. Ohtsuka, “Substrate for Semiconductor Apparatus Having a Composite Material”, U.S. Patent No. 5,409,864, April 25, 1995. 6. C. Zweben, “Advances in Composite Materials for Thermal Management in Electronic Packaging”, JOM, 1998, vol. 50, no. 6, pp. 47–50. 7. R.S. Fusco, “Composite Copper–Molybdenum Sheet”, U.S. Patent No. 4,950,554, August 21, 1990. 8. Metal Matrix Composites Corporation, http://www.mmccinc.com/thermal.htm. 9. “Development of Diamond–Metal Composite for HighPerformance Heat Sink”, SEI News, Sumitomo Electric Industries, vol. 297, http://www.sei.co.jp/sn/2002/06/06p7t.html. 10. Binary Alloy Phase Diagrams, Second Edition, edited by T.B. Massalski, H. Okamoto, P.R. Subramanian and L. Kacprzak, ASM International, Materials Park, OH, 1990, vol. 2, p. 1,504. 11. Ibid reference 10, p. 1,437. 12. J.L. Johnson and R.M. German, “Factors Affecting the Thermal Conductivity of W-Cu Composites”, Advances in Powder Metallurgy & Particulate Materials—1993, compiled by A. Lawley and A. Swanson, Metal Powder Industries Federation, Princeton, NJ, 1993, vol. 6, pp. 201–213. 13. J.L. Johnson, S. Lee, J-W Noh, Y-S Kwon, S.J. Park, R. Yassar, R.M. German, H. Wang, and R.B. Dinwiddie, “Microstructure of Tungsten Copper and Model to Predict Thermal Conductivity,” Advances in Powder Metallurgy & Particulate Materials—2007, compiled by J. Engquist and T.F. Murphy, Metal Powder Industries Federation, Princeton, NJ, part 9, pp. 99–110. 14. H. Walser, 2007, PLANSEE AG, Reutte, Austria, private communication. 15. J.L. Sepulveda and D.E. Jech, “Copper–Tungsten Metal Matrix Composites for Packaging Heat Sink Applications”, Tungsten and Refractory Metals 4—1998, edited by A. Bose and R.J. Dowding, Metal Powder Industries Federation, Princeton, NJ, 1998, pp. 393–400. 16. B. Yang and R.M. German, “Study on Powder Injection Molding Ball Milled W-Cu Powders”, Tungsten and Refractory Metals 2, edited by A. Bose and R.J. Dowding, Metal Powder Industries Federation, Princeton, NJ, 1994, pp. 237–252. 17. L. Kecskes, M. Trexler, B. Koltz, K. Cho and R. Dowding, “Mechanical Alloying Ef fects in Ball-Milled W-Cu Composites”, Advances in Powder Metallurgy & Particulate Materials—2000, compiled by H. Ferguson and D.T. Whychell, Sr., Metal Powder Industries Federation, Princeton, NJ, 2000, vol. 8, pp. 125–138. 18. C.C. Yu, R. Kumar and T.S. Sudarshan, “Synthesis of Tungsten Nano Composites”, Tungsten and Refractory Metals 3—1995, edited by A. Bose and R.J. Dowding, Metal Powder Industries Federation, Princeton, NJ, 1995, pp. 29–36. 19. L.P. Dor fman, M.J. Scheithauer, D.L Houck, A.T. Spitsberg and J.N. Dann, “Mo-Cu Composite Powder”, U.S. Patent 7,045,113, May 16, 2006. 20. L.P. Dor fman, M.J. Scheithauer, D.L Houck, A.T. Spitsberg and J.N. Dann, “Mo-Cu Composite Powder,”

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U.S. Patent 7,122,069, October 17, 2006. 21. L.P. Dorfman, M.J. Scheithauer, D.L Houck, M. Paliwal, G.T. Meyers and F.J. Vanskytis, “W-Cu Composite Powder,” U.S. Patent 5,956,560, September 21, 1999. 22. L.P. Dorfman, M.J. Scheithauer, D.L Houck, G.T. Meyers and F.J. Vanskytis, “W-Cu Composite Powder,” U.S. Patent 6,103,392, August 15, 2000. 23. H-K Kang and S.B. Kang, “Tungsten/Copper Composite Deposits Produced by a Cold Spray”, Scripta Materialia, 2003, vol. 49, pp. 1,169–1,174. 24. C. Zweben; "Ultrahigh-Thermal-Conductivity Packaging Materials”, Proc. 21st IEEE SEMI-THERM, 2005, IEEE, Piscataway, NJ, pp. 168–174. 25. C. Zweben, "High-Performance Thermal Management Materials,” Advanced Packaging February 2006, http://ap.pennnet.com/articles/article_display.cfm?Secti on=ARCHI&C=Feat&ARTICLE_ID=247014&KEYWORDS= Zweben&p=36. 26. K. Yoshida and H. Morigami, “Thermal Properties of Diamond/Copper Composite Material,” Microelectronics Reliability, 2004, Vol. 40, pp. 303–308. 27. H. Wildner, Plansee AG, 2007, private communication. 28. E. Neubauer, G. Korb, I. Smid, C. Eisenmenger-Sittner and H. Bangert, “Copper Carbon Composites Based on PVD Coated Reinforcements”, Advances in Powder Metallurgy & Particulate Materials—2004, compiled by R.A. Chernenkoff and W.B. James, Metal Powder Industries Federation, Princeton, NJ, 2004, part 9, pp. 27–37. 29. D.P.H. Hasselman and L.F. Johnson, "Ef fective Conductivity of Composites with Interfacial Thermal Barrier Resistance”, J. Comp. Materials, 1987, vol. 21, pp. 508–515. 30. P.R.W. Hudson, "The Thermal Resistivity of Diamond Heat-Sink Bond Materials,” J. Phys. D: Appl. Phys., 1976, vol. 9, pp. 225–232. 31. T. Schubert, H. Weidmueller, T. Weissgaerber and B. Kieback, "Carbide For mation in Copper–Carbon Composites and its Effect on Thermal Conductivity", ibid reference no. 13, part 9, pp. 10–18. 32. R. Bollina and M. Stoiber, "Ultra High Conductivity Diamond Composites", Proc. 2006 Powder Metallurgy World Congress, edited by K.Y. Eun and Y-S Kim, Korean Powder Metallurgy Institute, Seoul, Korea, part 2, pp. 922–923. 33. D.A. Mortimer and M. Nicholas, "The Wetting of Carbon and Carbides by Copper Alloys”, J. Mat. Sci., 1973, vol. 8, pp. 640–648. 34. O. Dezellus and N. Eustathopoulos, "The Role of van der Waals Interactions on Wetting and Adhesion in Metal/Carbon Systems”, Scripta Materialia, 1999, vol. 40, no. 11, pp. 1,283–1,288. 35. E. Neubauer, I. Smid, G. Kladler, G. Korb, C. Eisenmenger-Sittner and H. Bangert, "The Influence of Alloying Elements (Cr and T i) on the Thermal and Mechanical Characteristics of Copper–Carbon Composites based on Coated Carbon Fibers", Advances in Powder Metallurgy & Particulate Materials—2003, compiled by R. Lawcock and M. Wright, Metal Powder Industries Federation, Princeton, NJ, 2003, part 6, pp. 23–32. 36. S.M. DeVincent and G.M. Michal, "The Effect of Matrix Chemistry on the Properties of Graphite/Copper Composites", Proc. Control of Interfaces in Metal and

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Ceramics Composites, edited by R.Y. Lin and S.G. Fishman, The Minerals, Metals & Materials Society, Warrendale, PA, 1993, pp. 225-237. S.M. DeVincent and G.M. Michal, "Improvement of Thermal and Mechanical Properties of Graphite/Copper Composites Through Interfacial Modification”, J. Mat. Eng. Performance, 1993, vol. 2, no. 3 pp. 323–331. T. Oku, A. Kurumada, T. Sogabe, T. Oku, T. Kiraoka and K. Kuroda, "Effects of Titanium Impregnation on the Thermal Conductivity of Carbon/Copper Composite Materials”, J. Nuclear Materials, 1998, vol. 257, pp. 59–66. S.K. Datta, S.N. Tewari, J.E. Gatica, W. Shih and L. Bensen, "Copper Alloy-Impregnated Carbon–Carbon Hybrid Composites for Electronic Packaging Applications”, Metallurgical and Materials Transactions A, 1999, vol. 30A, pp. 175–181. E. Neubauer, P. Angerer and G. Korb, "Heat Sink Materials with Tailored Properties for Ther mal Management”, Proc. 28th ISSE 2005, pp. 251–257. E. Neubauer, I. Smid, S. Chotikaprakhan, D. Dietzel, B.K. Bein and G. Korb, "The Influence of the Thermal Contact Resistance on the Thermal Behaviour of Copper-Carbon Composites", Advances in Powder Metallurgy & Particulate Materials—2005, compiled by C. Ruas and T.A. Tomlin, Metal Powder Industries Federation, Princeton, NJ, 2003, part 9, pp. 16–26. E, Neubauer, "Interface Optimisation in Copper Carbon Metal Matrix Composites", 2003, PhD Thesis, Vienna University of Technology, Vienna, Austria. E. Neubauer, "Advanced Composite Materials with Tailored Thermal Properties for Heat Sink Applications”, presented at EPE IEEE 2007 (to be published). L. Pampaguian, E. Edtmaier, T. Janhsen, M. Ferrato, P. Chereau, S. Forero, T. Frey, A. Girmscheid, J. Helbig, F. Hepp, C. Laurent, A. Peiney, H.G. Wulz, "Non-Organic Matrix Materials Reinforced with Carbon Nanotubes for Space Applications”, presented at VIENNANO ’07, March 2007, Vienna, Austria. T. Ueno, “Metallic Material, Electronic Component, Electronic Device, and Electronic Optical Component Manufactured by Using the Metallic Material and Working Method of the Metallic Material”, U.S. Patent Application 2004/0187984 A1, September 30, 2004. T. Ueno, 2007, DEPT Corp., Tokyo, Japan, private communication. H. Walser, “T raditional and New Applications of Molybdenum Metal and Its Alloys”, Presented at 18th Annual General Meeting of the International Molybdenum Association, Vienna, Austria, Sept. 14, 2006. Metals Week, various issues, McGraw-Hill Publishing, New York, NY. ijpm

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COPPER-BASE PM— PAST, PRESENT & FUTURE William J. Ullrich*

INTRODUCTION The section in the Metal Powder Industries Federation (MPIF) Standard 35 Material Standards for PM Structural Parts, covering Copper and Copper Alloys, lists typical properties of four basic types of copper-base materials, namely, copper, brasses, nickel silver, and bronze. Table I has been excerpted from those data to highlight only those properties listed at their highest densities for non-leaded materials. Unfortunately, they are all inferior to their wrought counterparts and the market for these “structural” nonferrous powder metallurgy (PM) parts is small, with attendant much-slower growth compared with ferrous PM parts. The high cost of the raw materials (copper, nickel, tin, and zinc) preclude their use by design engineers except where mandated by any of their special properties, such as: • Electrical & thermal conductivity • Corrosion resistance • Bearing qualities • Workability, ductility • Appearance, color An advantage wrought metallurgists regularly employ is the response of all these copper-base materials to strain hardening by cold working. Table II1 cites the substantial increases in strength and hardness that can be accomplished with increasing levels of cold work. Wrought C52400 phosphor bronze, 10% D (C52400), is comparable with MPIF CT -1000 bronze, while wrought cartridge brass, 70% (C26000), is comparable with MPIF CZ-3000 brass. PM sintering temperatures are above the homogenizing and annealing (softening) temperatures, and are in the recrystallization/graingrowth region of these copper-base materials. The parts exit the furnace in the “soft anneal” condition, with high ductility/elongation, but with low strength and hardness. Unfortunately, PM parts producers can take only limited advantage of the substantial strength and hardness increases from cold working by re-pressing the parts. Therefore, those attempting to expand the market for copper-base structural PM parts have taken advantage of alternative strengthening mechanisms, including:

Just as the Bronze Age predated the Iron Age, so did the use of bronze in powder metallurgy (PM) precede the use of iron. Porous bearings account for the majority of bronze PM parts produced but iron still dominates the PM industry. Brass is the preferred metal for nonferrous PM structural parts. With the exception of self-lubricating bearings, bronze alloys have limited utility as PM structural parts, a reflection of the swelling intrinsic to sintering. Past approaches to increase the strength and hardness of traditional PM brasses and bronzes are reviewed and recent PM products, based on copper–aluminum alloys (aluminum bronzes), and copper–nickel–tin alloys (spinodal alloys), are discussed. There are a multitude of wrought and cast copper-base alloys, most of which respond to some form of strengthening mechanism. There is opportunity to simulate their behavior and to utilize the advantages of the PM process to create advanced copper-base particulate materials with enhanced and unique properties.

*Senior Metallurgist, ACuPowder International, LLC, 901 Lehigh Avenue, Union, New Jersey 07083-7632, USA; E-mail: [email protected]

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TABLE I. PROPERTIES OF COPPER AND COPPER ALLOYS* Ultimate Strength MPa (103 psi)

Material Designation

Description

C-0000-7 CZ- 1000- 11 CZ-2000-12 CZ-3000-16 CNZ-1818-17 CT- 1000- 13 (Re-pressed)

Copper "90/10 Brass" "80/20 Brass" "70/30 Brass" "Nickel Silver" "90/10 Bronze"

190 160 240 230 230 150

(28.0) (23.0) (35.0) (34.0) (34.0) (22.0)

Yield Strength (0.2%) MPa (103 psi) 60 80 120 130 140 110

Elongation (in 25.4 mm) %

(8.5) (12.0) (17.0) (19.0) (20.0) (16.0)

Unnotched Charpy Impact Energy J (ft.·lbf.)

25.0 12.0 18.0 17.0 11.0 4.0

61 42 61 52 33 5

Transverse Rupture Strength MPa (103 psi)

(45.0) (31.0) (45.0) (38.0) (24.0) (4.0)

N/D 360 480 590 500 310

N/D (52) (70) (86) (73) (45)

Apparent Hardness Density RH g/cm3 30 ** 80 82 92 90 82

8..3 8.1 8.0 8.0 7.9 7.2

Mechanical property data derived from laboratory prepared test specimens sintered under commercial manufacturing conditions Strengths represented are minimum values *Adapted from MPIF Standard 35, Materials Standards for PM Structural Parts, and reprinted by permission, the Metal Powder Industries Federation, Princeton, NJ **After re-pressing, the hardness of C-0000-7 is ~60 RH TABLE II. PROPERTIES OF WROUGHT PHOSPHOR BRONZE AND CARTRIDGE BRASS AT VARIOUS TEMPERS1 C52400 (Phosphor Bronze, 10% D)* Temper Designation 0.100mm 0.050 mm 0.035 mm 0.015mm Quarter Hard Half Hard Hard Extra Hard Spring Extra Spring

U.T.S. MPa (103 psi)

Elongation %

Hardness RB

455 (66)

68

55 B

572 690 793 841 883

32 13 7 4 3

92 B 97 B 100 B 101 B 103 B

(83) (100) (115) (122) (128)

C26000 (Cartridge Brass, 70%)** U.T.S. MPa (103 psi) 303 324 338 366 372 428 524 593 648 683

(44) (47) (49) (53) (54) (62) (76) (86) (94) (99)

Y.S. MPa (103 psi) 76 90 117 152 276 359 434 448 448 448

(11) (13) (17) (22) (40) (52) (63) (65) (65) (65)

Elongation %

Rockwell Hardness

66 62 57 54 43 25 8 5 3 3

54 F 64 F 68 F 78 F 55 B 70 B 82 B 88 B 91 B 93 B

*nominal 90 w/o Cu-10 w/0 Sn-0.3 w/o P **nominal 70 w/o Cu-30 w/o Zn • Solid solution hardening • Precipitation/age hardening • Quench hardening • Transformation hardening • Order hardening • Micro-duplex hardening • Dispersion strengthening • Spinodal decomposition Each of these approaches to strengthening, in the context of the PM processing of copper-base compositions, is now considered. SOLID-SOLUTION HARDENING Bronze, brass, and nickel silver alloys owe their strength to solid-solution hardening. The three alloying elements (solutes) nickel, tin, and zinc have dif ferent solubilities in copper. Their strengthening potency is related to their atomic

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radii, with tin being more potent than zinc, having the larger radius, compared with copper (solvent). Figure 1 shows the differences between tin and zinc on hardness and elongation. 2 Although it takes much more zinc in the base copper to strengthen the resultant alloy, the cost of tin is almost four times the cost of zinc, which itself is only one half the cost of the base metal copper. Table III lists the typical constituents used to fabricate MPIF Standard 35 copper and copper alloy PM parts. Note that only the bronzes offer a wide array of options to choose from in order to leverage properties. BRONZE PM Historically, bronze predates iron and brass PM with numerous early (1920s) U.S. patents primarily covering porous bearing applications. A Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Figure 1. Comparison of the effect of aluminum, tin, and zinc, as solid-solution strengtheners of copper, on hardness and ductility2

TABLE III. CONSTITUENTS IN COPPER AND COPPER ALLOYS (NON-LEADED)* Copper (C-0000) Brass (CZ-1000) Brass (CZ-2000) Nickel Silver (CNZ-1818) Bronze (CT-1000)

Elemental copper Alloy of nominal 90 w/o Cu-10 w/o Zn Alloy of nominal 80 w/o Cu-20 w/o Zn Alloy of nominal 70 w/o Cu- 30 w/o Zn Mix of 90 w/o elemental Cu-10 w/o elemental Sn Mix of 80 w/o elemental Cu-20 w/o alloy of 50 w/o Cu - 50 w/o Sn Prealloy of 90 w/o Cu-10 w/o Sn Diffusion alloy of 90 w/o Cu-10 w/o Sn Combinations of above four Addition of 8.4 w/o Phos Cu alloy

*Adapted from MPIF Standard 35, Materials Standards for PM Structural Parts, and reprinted by permission, the Metal Powder Industries Federation, Princeton, NJ unique attribute of sintering mixes of elemental copper and tin powders in a 90/10 weight ratio, is the ability to form porous products with interconnected porosity. These bearings can be filled with oil (10 v/o to 25 v/o) in order to supply a continuous lubricating film in use. Unfortunately, the phenomenon of rapid growth followed by slow shrinkage during the liquidphase sintering of elemental copper–tin mixes, prevents the formulation of a dense, strong structural PM bronze part. As described by German,3 “During heating, the tin melts and wets the copper, leaving a pore. A small dimensional increase (swelling) occurs at 232°C (450°F) when the tin melts, and swelling is evident up to approximately 700°C (1,292°F). The swelling represents the rapid diffusion of tin into the copper, creating pores at the sites previously occupied by the tin. With proVolume 43, Issue 5, 2007 International Journal of Powder Metallurgy

longed heating, the alloy homogenizes to form a single-phase compact. Typically densification is delayed until after homogenization.” MPIF Standard 35, Materials Standards for PM Structural Parts (2007 Edition), lists only one bronze alloy, CT-1000-13, and shows properties only in the re-pressed condition. I assume this is a high-density bearing material, which achieves higher density, strength, and hardness by repressing. In order to achieve even higher strengths, powder suppliers make use of several variants and additions to elemental copper–tin mixes, either alone or in combination: • Copper powder particle size and shape • Tin powder particle size • Prealloyed 50/50 (by weight) copper–tin powder additions

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• Prealloyed 90 w/o Cu-10 w/o Sn and 95 w/o Cu-5 w/o Sn powder additions • Phosphorus–copper alloy powder (8.4 w/o P) additions The technique of adding phosphorus–copper, brings PM bronze more in line with its most popular wrought counterpart, phosphor bronze, 10% D (C52400). During the melting/alloying of bronze, 15 w/o phosphorus–copper shot is added to deoxidize the bronze melt and increase fluidity. The phosphorus–copper level is adjusted to leave from 0.03 w/o to 0.35 w/o P, which protects the metal from re-oxidation and strengthens the bronze alloy. To introduce phosphorus into mixes of elemental copper and tin powders, PM producers add phosphorus–copper alloy powder, which contains nominally 8.4 w/o P, with a eutectic melting point of 714°C (1,320°F). The phosphorus activates the sintering mechanism, with a negative dimensional change (shrinkage) with higher density and strength. Tin and phosphorus strengthen copper by forming a solid solution. These solute atoms substitute for the copper atoms resulting in a singlephase solid solution. The increase in strength brought about by alloying with tin is due to its large atomic radius compared with that of the copper matrix. Unfortunately, the resultant bronze alloy cannot be precipitation hardened due to the extremely slow precipitation kinetics.2 Table IV lists the published properties of CT1000-13 in the “re-pressed” condition, compared with those of three commercial products 4,5 employing one or more of the five strengthening variants cited. CT-1000-13 is the only structural bronze alloy listed in MPIF Standard 35. I believe

the properties are in the as-sintered state, and would be strengthened further by re-pressing. However, none of these products can be considered as viable PM alternatives to wrought phosphor bronze, 10% D (C52400). Their main drawback is the porosity which forms during growth and which occurs when elemental tin powder melts and alloys with the copper matrix during sintering. PREALLOYED PM BRONZE STRUCTURAL PARTS Starting with a prealloyed bronze powder, growth and the development of porosity during sintering are eliminated. The simplest method of atomization employs high-pressure air. Unfortunately, this technique generates copper and bronze particles that are spherical or near spherical and which do not develop sufficient green strength during conventional compaction to be useful. Conversely, all the copper–zinc brass alloys will produce irregularly shaped particles via air atomization with adequate green strength. Water atomization, with its high mass-to-metal ratio, pressures, and cooling rates, generates irregular particles with adequate green strength. However, there are the added manufacturing steps of filtering and drying of the powder. Mathews6 capitalized on the simplicity of air atomization, coupled with the effect of zinc in creating irregularly shaped particles. An alloy of composition 89 w/o Cu-9 w/o Sn-2 w/o Zn was utilized for the production of structural bronze PM parts. After compaction from 303 MPa (44,000 psi) to 579 MPa (84,000 psi), followed by sintering at 843°C (1,550°F) for 30 min in dissociated ammonia, dimensional change (shrinkage) was in

TABLE IV. COMPARISON OF PROPERTIES OF CONVENTIONAL PM BRONZES4,5 Designation Ultimate Tensile Strength MPa (103 psi) Yield Strength (0.2%) MPa (103 psi) Elongation (in 25.4 mm) % Transverse Rupture Strength MPa (103 psi) Apparent Hardness RH Density g/cm3

46

MPIF CT- 1000- 13 (Re-pressed)

ACuPowder 5521

Greenback GB-P

NJZ w/1403 & 1501

150 (22.0)

156 (22.6)

242 (35.1)

321 (46.6)

110 (16.0) 4.0

83 (12.0) 14.6

27

40

310 (45) 82 7.20

439 (63.6) 82 6.61

583 (84.5) 74 7.31

88 7.92

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TABLE V. PROPERTIES OF PREALLOYED BRONZE PM PARTS7,8 Grade/Alloy Type

Tensile Strength MPa 103 psi Yield Strength MPa 103 psi Elongation (%) Transverse Strength* MPa 103 psi Apparent Hardness Density (g/cm3) Re-pressed @ MPa 103 psi Yield Strength MPa 103 psi Transverse Strength MPa 103 psi Apparent Hardness Density (g/cm3)

USB B-413-L USB B-4131-L 89 w/o Cu-9 w/o Sn- 88 w/o Cu-9 w/o Sn2 w/o Zn 2 w/o Zn -1 w/o Fe Air Atomized Air Atomized

ACu HS-4000A ACu HS-4000 89 w/o Cu-9 w/o Sn- 90 w/o Cu-10 w/o Sn 2 w/o Zn Air Atomized Diffusion Alloyed 310 45

276 40

"European" -325 Mesh 90 w/o Cu-10 w/o Sn Water Atomized

138 20

145 21

131 19 40

145 21 26

559 81 86 RH 7.9

572 83 30 RB 7.9

690 100 40 RB 8.2

655 95 90 RH 8.3

669 97 68 RB 8.4

414 60

414 60

552 80

552 80

952 80

193 28

200 29

593 86 48 RB 8.2

683 99 45 RB 8.3

1,100 160 80 RB 8.4

828 120 61 RB 8.4

731 106 84 RB 8.5

* Transverse rupture strength values are misleading due to significant ductility/bending the range -1.8% to -0.3%. Property data for this alloy (USB B-413-L) and for USB B-4131-L (the same base alloy but with 1 w/o carbonyl iron addition) are cited in Table V.7 A third method of producing irregularly shaped bronze alloy particles is by diffusion alloying. Irregular copper powder is physically mixed with 10 w/o of a much finer tin powder. This mixture is heated under a protective atmosphere at temperatures from 400°C to 600°C (750°C to 1,110°F), which are above the melting point of tin (232°C (449°F)). The resultant mass of powder particles can attain any one of three stages: • “Diffusion Bonded”—the tin particles adhere to the larger copper particles • “Partially Alloyed”—the molten tin spreads over the surfaces of the copper particles and into fissures and cracks and partially diffuses into the copper • “Fully Alloyed”—diffusion of the tin into the copper particles is complete and the copper particles are fully diffusion alloyed Agglomeration of the mass of particles occurs Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

during heating. However, with judicious grinding techniques the sinter cake can be disintegrated, retaining most of the original irregularity of the starting copper powder. It appears that the swelling caused by the tin melting and diffusing into the copper occurs during diffusion alloying. The resultant bronze alloy powder behaves much like a fully prealloyed and atomized bronze powder. Thus, it will shrink after compaction and sinter to a high density and strength. Table V lists the properties attained from the three types of prealloyed bronze powders: • Air atomized: 89 w/o Cu-9 w/o Sn-2 w/o Zn (Figure 2) • Water atomized: 90 w/o Cu-10 w/o Sn (Figure 3)8 • Diffusion alloyed: 90 w/o Cu-10 w/o Sn (Figure 4) In some cases the products listed in Table V may contain proprietary additives. Figures 2, 3,8 and 4 are representative scanning electron micrographs (SEMs) illustrating particle morphologies.

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Figure 2. Representative morphology of air-atomized 89 w/o Cu-9 w/o Sn-2 w/o Zn alloy powder. SEM

Figure 3. Representative morphology of water-atomized 90 w/o Cu10 w/o Sn alloy powder.8 SEM

Figure 4. Representative morphology of diffusion-alloyed 90 w/o Cu-10 w/o Sn powder. SEM

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PM BRASSES Material properties of three unleaded grades of PM brass are listed in Table I. Note that yield strength, transverse rupture strength, and apparent hardness increase with increasing zinc content. Matthews9 has stated that 90 w/o Cu-10 w/o Zn non-leaded, 80 w/o Cu-20 w/o Zn leaded, and 70 w/o Cu-30 w/o Zn non-leaded brasses are manufactured to yield properties in conformance with Military Specification MIL-B-11552 (MR), so their base chemistries cannot be modified. Matthews9 also found that adding 3 w/o carbonyl iron powder to 70/30 brass increased ultimate and yield strength, and apparent hardness, but with some loss in ductility. Table VI lists the processing conditions, and Figures 5, 6, 7, and 8 plot the strength, hardness, and elongation for the following brasses: 90/10, 80/20 (leaded), 70/30, and 70/30 with 3 w/o iron. Again, we see increasing strength and hardness values with increasing zinc content. Note the differences in response to compaction and re-pressing pressures. I have estimated the values from Figures 5, 6, 7, and 8 for the 70/30 brasses, with and without the 3 w/o iron powder addition, and listed them in Table VII. The properties listed are for specimens compacted at either 414 or 690 MPa (30 or 50 tsi), and sintered at 899°C (1,650°F) for 30 min in a dissociated ammonia atmosphere. Note the increase in strength and hardness brought about by the 3 w/o iron powder addition, while elongation decreases. Brasco™ is an alloy of 67 to 70 w/o copper, 3.2 to 3.8 w/o cobalt, balance zinc. It was introduced circa 1974 as Grade 1170 brass powder by the Zinc Corporation of America. The goal was to increase strength and hardness while avoiding the necessity for the additional post-sintering operations of re-pressing, followed by re-sintering, to relieve work hardening and restore ductility. Brasco™ owes its superior strength and hardness to the precipitation of cobalt that occurs when the sintered compact cools to room temperature in the normal sintering cycle.10 In particular, the higher yield strength is cited which offers a potential market for PM parts meeting the ASME Boiler and Pressure Vessel Code. Table VIII lists the properties10 of grade 1170 Brasco sintered to densities of 7.7 and 7.9 g/cm3, per the recommended conditions of preheat at 549°C (1,020°F), and a sintering temperature of 880°C (1,615°F) for 30 min in dissociated ammoVolume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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TABLE VI. PROCESS CONDITIONS (COMPACTION AND SINTERING) FOR BRASSES, AND RESULTING DENSITIES9 Compact Density (g/cm3) Processing Conditions

70/30 (3 Fe)

70/30

80/20 (1.5 Pb)

90/10

1st press 414 MPa (30 tsi) 1st press 690 MPa (50 tsi) 2nd press (690 MPa (50 tsi) 3rd press 690 MPa (50 tsi) Presinter °C (°F)/0 min Full sinter °C (°F) Full sinter (min) United States Bronze Grade Designation

7.32 7.68 8.12 8.29 871 (1,600) 900 (1,650) 30 B-124 X

7.30 7.73 8.10 8.25 871 (1,600) 900 (1,650) 30 B-124

7.60 7.85 8.37 8.54 871 (1,600) 900 (1,650) 30 B-129

7.80 8.28 8.28 8.29 871 (1,600) 900 (1,650) 30 B-101

Figure 5. Ultimate tensile strength of sintered brasses at various density levels (Table VI)9 1 MPa = 145 psi

Figure 6. Yield strength (tension) of sintered brasses at various density levels (Table VI)9 1 MPa = 145 psi

Figure 7. Elongation of sintered brasses at various density levels (Table VI)9

Figure 8. Apparent hardness of sintered brasses at various density levels (Table VI)9

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TABLE VII. PROPERTIES OF 70/30 BRASS AND 70/30 BRASS (3 w/o IRON)9 Alloy Compaction Pressure MPa (103 psi) Ultimate Tensile Strength MPa (103 psi) Yield Strength MPa (103 psi) Elongation ( %) Apparent Hardness

70/30

70/30 + 3 w/o Fe

414 (60)

690 (100)

414 (60)

690 (100)

248 (36)

276 (40)

293 (42.5)

297 (43)

90 (13) 26 88 RH

110 (16) 27.5 94 RH

138 (20) 15 32 RB

145 (21) 16 50 RB

TABLE VIII. AS-SINTERED & HEAT-TREATED PROPERTIES OF BRASCO™10 Condition

As-Sintered As-Sintered Heat-Treated

Sintered Density (g/cm3)

7.7 Compaction Pressure MPa 428 (62) (103 psi) Sintering Temperature °C 880 (°F) (1,615) Ultimate Tensile Strength MPa 310 (45) (103 psi) Yield Strength (0.2% offset) MPa 248 (36) (103 psi) Transverse Rupture Strength MPa 93 (86) (103 psi) Elongation (in 25.4 mm), % 7 Unnotched Charpy Impact Energy 6.8 J (ft.·lbf.) (5) Apparent Hardness (RB) 37

7.9

7.85

552 (80) 880 (1,615)

860 (1,580)

345 (50)

372 (54)

262 (38)

317 (46)

669 (97) 10 8.1 (6) 45

5

58

nia. Table VIII shows the effects of heat treatment, i.e., quenching to room temperature in oil, followed by aging for 4 h at 450°C (842°F). Note that quenching after sintering retains the cobalt in solid solution, resulting in mechanical properties that approach those of conventional sintered brass. Reheating after quenching produces extensive precipitation of cobalt, increasing strength properties above those in the as-sintered state. ALUMINUM BRONZE Figure 1 compares the potency of aluminum, tin, and zinc solute atoms in copper in relation to hardness and ductility. Copper with 11 w/o aluminum responds to a heat treatment of homoge-

50

nization, quenching, and tempering, to achieve even higher strength and hardness. Conversely, the tin bronze and copper–zinc brasses can only be strengthened by cold working. Matthews11 recognized the superior properties of wrought aluminum bronze alloys and demonstrated that a PM aluminum bronze system (5–11 w/o Al) exhibited improved properties over standard copperbase PM alloys. Aluminum bronzes12 with 9 w/o to 11.5 w/o aluminum and nickel–aluminum bronzes with 8.5 w/o to 11.5 w/o aluminum respond in a practical way to quench hardening by a martensitictype reaction. Alloys higher in aluminum content generally are too susceptible to quench cracking, whereas those with lower aluminum contents do not contain enough high-temperature beta phase to respond to quench treatments. Alpha aluminum bronzes 12 are aluminum bronzes that contain <9 w/o aluminum, or <8.5 w/o aluminum with up to 3.0 w/o iron. They are essentially single-phase alloys, except for fine iron-rich particles in those alloys that contain iron. For alpha aluminum bronzes, effective strengthening can be attained by cold work. Complex (alpha–beta) aluminum bronzes12 are aluminum bronzes in which microstructures contain more that one phase, to the extent that beneficial quench-and-temper treatments are possible. These copper aluminum alloys, with and without iron, are heat treated by procedures similar to those used in the heat treatment of steel, and have isothermaltransformation diagrams that resemble those of plain carbon steels. For these alloys, the quench-hardening treatment is essentially a high-temperature soak, intended to dissolve the alpha phase into the beta phase. Quenching results in a hard room-temperature beta martensite structure; and subsequent tempering re-precipitates fine alpha needles in the structure, forming a tempered beta martensite. Figures 9 and 10 show the increase in strength and hardness as the aluminum content increases from 5 to 11 w/o.11 Properties are also shown for re-pressed material and for the heat-treated alloys containing 11 w/o aluminum. Commercially available PM alloys are Cubraloy 5 with good ductility for cold working, and Cubraloy 11, which responds to heat treatment. Dixon and Mills13 explored the potential of PM aluminum bronzes for automotive applications, They concluded that, in comparison with PM bronze bearings, cast 660 bronze, and cast aluminum bronze, their material performed well in Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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relation to strength, wear capability, and coolness of running. Subsequently, Dixon14 compared the response of a new high-performance PM bronze bearing with machined cast 660 and 62 bronze bearings in relation to load capacity, fatigue resistance, maximum operating temperature, con-

Figure 9. Tensile strength of sintered aluminum bronzes11 1 MPa = 145 psi

Figure 10. Elongation and apparent hardness of sintered aluminum bronzes11

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

formability and embeddability, resistance to seizure, hardness, and wear resistance. Dixon also examined an admixture of elemental powders in the ratio: 80 w/o Cu-11 w/o Al-5 w/o Fr-4 w/o Ni with added lubricant. 15 It is claimed that during sintering in 100 v/o dissociated ammonia, Fe3Al and Ni3Al form, the nickel alloys with the copper, and final alloying of all the phases results in a microstructure with the appearance of a multi-phase material. Fully dense properties are claimed at 80 w/o density. COPPER–NICKEL–TIN SPINODAL ALLOYS Since the 1920s, the copper-rich corner of the ternary Cu-Ni-Sn equilibrium phase diagram has been studied in relation to the significant agehardening response of these alloys. It was not until the mid 1970s that the hardening was attributed to a spinodal decomposition. The most common wrought spinodal alloy, used primarily as rolled strip in electrical contacts, is 15 w/o Ni8 w/o Sn-balance copper (C79200). As explained by Cribb,16 “Spinodal decomposition takes place spontaneously and needs no incubation period. Instead of the classical nucleation-and-growth process, spinodal decomposition is a continuous-diffusion process in which the original alloy decomposes into two chemically different zones that have identical crystal structural. Each enriched cluster in the spinodally hardened alloy is on the nanoscale, and is continuous throughout the grains up to the grain boundaries. Spinodal decomposition in the copper–nickel–tin alloys triples the yield strength of the base metal. The high strength that results from the spinodal decomposition of these alloys has been attributed to the coherency strains produced by the uniform and high-number-density dispersions of tin-rich perturbations in the copper matrix. Certain conditions must be fulfilled for spinodal decomposition hardening. The solidstate phase diagram of a spinodal system must contain a miscibility gap, a region in which the single-phase alloy separates into compositionally different regions. The alloying elements must also have sufficient mobility in the parent matrix at the miscibility gap to allow inter-diffusion.” The heat treatment steps16 for spinodal decomposition include: • Homogenization at a temperature above the miscibility gap, to develop a uniform solid solution of a single phase

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• Rapid quenching to room temperature to retain the solid-solution state • Reheating to a temperature within the spinodal region to initiate the reaction, and holding for sufficient time to complete the spinodal decomposition Alloys strengthened by spinodal decomposition develop a characteristic modulated microstructure. Resolution of this fine-scale structure is beyond the range of optical microscopy and is only resolvable by skillful transmission electron microscopy. Figure 11 compares precipitation (or age) hardening with spinodal decomposition.17 In the latter, waves of a second phase of material grow within the grain. Dislocations are stopped at the boundaries between the two different phases within each grain. Reinshagen18 has documented the compaction, sintering, and heat treating/aging of a wateratomized 15 w/o Ni-8 w/o Sn-balance copper alloy powder to produce strong PM parts. In relation to 316L stainless steel, Cu-30 w/o Zn, and Cu-10 w/o Sn with 0.2% offset yield strengths of 349 MPa (50,000 psi), 138 MPa (20,000 psi), and 124 MPa (18,000 psi), respectively, the spinodal alloy exhibits a 0.2 w/o offset yield strength of 552 MPa (80,000 psi).19 Watson20 studied property improvements in PM spinodal alloys. Variables included in the study were: Composition: • Base bronze powders • Nickel addition, type and w/o • Lubricant type • Compaction pressure Sintering: • Batch and continuous belt furnaces • Temperature, time, and atmosphere • Cooling/quench rate Re-pressing pressure Heat treatment • Temperature, time, and atmosphere It was found that three types of bronze alloy powder are suitable: • Water atomized 90 w/o Cu-10 w/o Sn bronze (Figure 3) • Air atomized 89 w/o Cu-9 w/o Sn-2 w/o Zn bronze (Figure 2) • Dif fusion alloyed 90 w/o Cu-10 w/o Sn bronze (Figure 4) Carbonyl nickel, such as Inco 123 Ni (Figure 12), worked well.

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Figure 11. (a) precipitation hardening, and (b) spinodal decompostion17

Figure 13 shows the effect of nickel content (6–15 w/o) on transverse rupture strength and apparent hardness. The nickel content was kept at 8.5 w/o for subsequent tests. Figure 14 shows the effect of varying the heat-treat/aging temperature from 350°C to 450°C (662°F to 842°F). The following processing conditions were recommended: • Compaction at 552 MPa (40 tsi) • Sintering/homogenization at 845°C (1,553°F) for 45 min with a minimum of 10 v/o hydrogen • Fast cooling from the hot zone via “Varicool,” “Versacool,” or similar fast-cooling method used for sinter hardening; quenching is an alternate method • Heat treatment at 350°C to 400°C (662°F to 752°F) for 90 min under nitrogen or other protective atmosphere Table IX lists the sintered and age-hardened properties, following these guidelines.20 Note the properties of the same bronze base without the 8.5 w/o Ni addition. Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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TABLE IX. COMPARISON OF PROPERTIES BEFORE & AFTER ADDING NICKEL20 Property

No Nickel

Ultimate Tensile Strength MPa (psi) 313 (45,400) Yield Strength (0.2%) MPa (psi) 133 (19,300) Transverse Rupture Strength, MPa (psi) Bent Elongation (%) 40 % Unnotched Charpy Impact Energy J (ft.·lbf.) 95 (70) Apparent Hardness (RB) 40

8.5 w/o Nickel & Heat Treated 465 (67,400) 371 (53,900) 896 (130,000) 0.8 7.7 (5.7) 70

Figure 12. Representative morphology of carbonyl nickel powder. SEM

Figure 13. Transverse rupture strength and apparent hardness as a function of nickel content in a spinodal composition20

CONCLUSION On concluding 46 years as a metallurgist at a nonferrous powder production facility, I have experienced accelerated requests from both PM parts producers and end users, for stronger, more wear-resistant materials. Usually the goal is to match the properties of an existing wrought alloy with the closest PM counterpart. Early attempts are reviewed, starting with conventional (historic) brasses and bronzes, making use of some of the many strengthening mechanisms copper -base material respond to. Past and current attempts have been accomplished by both powder producers and parts manufacturers. Others fall in the category of powder producer/shape producer. It is my hope that this selective review will spur interest in exploring the multitude of cast and wrought copper-base alloys, coupled with the advantages and flexibility of the PM process, to leverage properties. Future developments will be accomplished by those with the imagination and desire to do so. ACKNOWLEDGEMENTS The author wishes to thank Inco, New Jersey & Canada, for generating the scanning electron microscope images. I am also indebted to Gail DeSantis and Kenneth Watson for their computer assistance, and lastly, to Edul Daver for his patience in allowing the completion of this project. REFERENCES

Figure 14. Transverse rupture strength and apparent hardness as a function of heat-treating temperature20

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

1. Standards Handbook, Part 2—Alloy Data, Wrought Copper & Copper Alloy Mill Products, Eighth Edition, Copper Development Association, Inc., Greenwich, CT, 1985, pp. 80–116. 2. C.R. Brooks, Heat Treatment, Structure and Properties of Nonferrous Alloys, 1982, American Society for Metals,

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Fast, Efficient Fine Grinding . . . Wet Or Dry Model 100SC

Model 1-S

Inventors and Developers of Attritors.

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Metals Park, OH, 1982, pp. 305–313. 3. R.M. German, Powder Metallurgy & Particulate Materials Processing, 2005, Metal Powder Industries Federation, Princeton, NJ, p. 246. 4. “Greenback GB-P Hi-Strength Bronze Premixes Offer Economy and Strength”, (circa 1980s), Greenback Technical Data, Greenback Industries, Inc., Greenback, TN 5. “High Strength Structural Parts”, 1965, NJZ Technical Information, New Jersey Zinc Co., New York, NY 6. P.E. Mathews and K.C. Ramsey, “Composition for Atomized Alloy Bronze Powders”, U.S. Patent No. 4,169,730, October 2, 1979. 7. “Bronze Powder (89Cu–9 Sn–2 Zn)” Bulletin 304, (circa 1970s), United States Bronze Powders, Inc., Flemington, NJ 8. E. Peissker, “Metal Powders”, 1986, Norddeutsche Affinerie, Hamburg, Germany, p. 27 9. P.E. Matthews, “The Mechanical Properties of Brass and Developmental Non-Ferrous P/M Parts”, Int. J. Powder Metall., 1969, vol. 5, no. 4, pp. 59–69. 10. K.E. Geary “High Strength Brass Powder”, 1979, The New Jersey Zinc Co., Bethlehem, PA 11. P.E. Matthews, “Cubraloy, A New Development in Aluminum– Bronze Powder Metallurgy”, 1971 Fall Powder Metallurgy Conference Proceedings, edited by S. Mocarski, Metal Powder Industries Federation, Princeton, NJ, 1971, pp. 205–216 12. “Hardening/Copper–Aluminum (Aluminum Bronze) Alloys”, Metals Handbook, Desk Edition, Second Edition, edited by J.R. Davis, ASM International, Materials Park, OH, 1998, pp. 1,041–1,042. 13. J.N. Dixon and C. Mills, “Development of P/M Aluminum Bronze for Automotive Applications”, Proceedings of the Powder Metallurgy Aluminum & Light Alloys for Automotive Applications Conference, edited by W.F. Jandeska, Jr., and R.A. Chernenkoff, Metal Powder Industries Federation, Princeton, NJ, 1998, pp. 67–73. 14. J.N. Dixon, “A Comparison of New High Performance P/M Bronze Bearing to Machined Cast 660 and 62 Bronze Bearings”, Advances in Powder Metallurgy & Particulate Materials—2004, compiled by R.A. Chernenkoff and W. B. James, Metal Powder Industries Federation, Princeton, NJ, 2004, vol. 3, part 12, pp. 35–48. 15. J.N. Dixon, “Powdered Metal Admixture and Process”, U.S. Patent No. 6,132,486, October 17, 2000. 16. W.R. Cribb, “Copper Spinodal Alloys for Aerospace”, Advanced Materials & Processes, 2006, vol. 164, no. 6, p. 44. 17. M. Gedeon, “Thermal Strengthening Mechanisms”, 2000, Technical Tidbits, Brush Wellman Inc., Cleveland, OH, vol. 2, no. 12. 18. J.H. Reinshagen, “Powder Metallurgical Processing for Manufacturing Copper–Nickel–T in Spinodal Alloy Articles”, U.S. Patent No. 4,681,629, July 21, 1987. 19. “Ametek’s Spinodal Alloy Powder”, 1988, Ametek Tech. Report 1030, Ametek, Eighty Four, PA 20. K. Watson, W. Ullrich, W. Morrissey and R. Gotham, “Improving Properties Through the Use of Spinodal Alloys”, Advances in Powder Metallurgy & Particulate Materials—2007, compiled by J. Engquist and T.F. Murphy, FAPMI, Metal Powder Industries Federation, Princeton, NJ, 2007, vol. 2, part 7, pp. 80–94. ijpm

Machinery use and product under one or more U.S. and foreign patents and patent applications. © 2000, Union Process. All rights reserved.

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1299-38

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COPPER PM: NEW DEVELOPMENTS & APPLICATIONS

METAL POWDER INJECTION MOLDING OF COPPER AND COPPER ALLOYS FOR MICROELECTRONIC HEAT DISSIPATION Randall M. German* and John L. Johnson**

INTRODUCTION Powder injection molding of copper and copper alloys is not new. Trials using PIM to fabricate electrical connectors demonstrated technical success long ago, but encountered cost barriers. However, the increasing power requirements and decreasing size of high-performance microprocessors present heat-dissipation challenges in microelectronic package designs that are compatible with PIM. Design factors require the dissipation of significant amounts of power over a small physical area. New heat sink designs attempt to handle these increasing thermal loads using microchannels, heat pipes, and aerodynamic fins. Thus, renewed interest exists in PIM as a cost-effective fabrication route for the production of large quantities of complex heat sinks and heat pipes.

Powder injection molding (PIM) has been applied to copper and copper alloys for several years. Many powder and process variants have been demonstrated, and recent work has been directed to applications associated with heat dissipation in electronic systems. This focuses attention on unalloyed copper with high thermal and electrical conductivity and on bronze for aesthetic non-structural uses. This paper provides a brief history of the field and the ensuing rationalization of the powder, process, and properties to the application. Fundamentally, PIM of copper requires a balance between the optimal processing options that deliver the desired properties and the conflicting dictates of low-cost processing. A key to success often is tied to oxygen control in the copper powder.

HEAT DISSIPATION IN MICROELECTRONICS The most widely used method for extracting heat from a microprocessor is to connect it to a heat sink, which might be air cooled, either actively or passively. Heat sinks usually have fins to increase their surface area, which increases the amount of heat that they can release to the ambient air. Many early heat sinks were extruded or machined from aluminum. Extrusion is a highly automated, low-cost, high-volume process, but it inherently limits the fin geometry. Further, the alloys that are easy to extrude do not have a high thermal conductivity, while the high thermal conductivity alloys resist extrusion. Machining or die casting can produce desirable fin arrays, but the designs are not spaced close enough to meet the power dissipation requirements of the latest microprocessors.1 As is often the case, the alloys that lower the production cost exhibit low thermal performance, while the high-per-

*CAVS Chair Professor, Mechanical Engineering, Center for Advanced Vehicular Systems, Mississippi State University, 200 Research Boulevard, Starkville, Mississippi 39759, USA; E-mail: [email protected], **ATI Alldyne, 7300 Highway 20 West, Huntsville, Alabama 35806, USA; E-mail: [email protected]

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formance alloys are difficult to process. This situation has led to novel designs, such as folded-fin heat sinks and integrated heat pipes formed from copper. Folded-fin heat sinks can give a two-fold improvement over the performance of extruded heat sinks, but with an increased cost. Integrated heat pipes can give additional performance improvement, but currently cost five to ten times that of extruded heat sinks. Copper is chosen over aluminum for applications that require high thermal conductivities, especially where a low thermal expansion coefficient is required to reduce thermal fatigue problems. Compared with aluminum alloys, copper is more difficult to extrude, stamp, cast, or machine. Thus, PIM of copper has the potential to provide a low-cost, high-volume process that can meet both the geometry and property requirements.2 Copper powders are available in a wide range of particle sizes, some of which are suitable for PIM. Alternatives to copper include tungsten–copper (high density) and aluminum matrix composites (Al-SiC, Al-Si) which are relatively expensive. AESTHETIC APPLICATIONS FOR BRONZE One of the new applications for PIM is in logos and designer components. These go beyond the early applications in wrist watches to include product identification tags on luxury luggage, computers, printers, and golf clubs. Bronze is a durable and low-cost material that is often used for these applications. The use of injection molding to form bronze was demonstrated in the 1980s, and production of medallions, art objects, and related products started in the 1990s. Recent data have shown that PIM bronze is highly passive in general atmospheric corrosion and oxidation environments.3 Most desirable is the ease of sintering possible with bronze, making it compatible with some applications in large production quantities if adapted for common consumer items, especially as a means to deter counterfeiting (for example, gambling tokens). Low-pressure injection molding of bronze was commercialized in the late 1990s for the fabrication of porous structures (filters) and art objects.4 OPEN LITERATURE To understand the current situation in copper and copper alloys, a few comments are appropriate on prior PIM research. The first published reports on PIM copper and copper alloys came out of

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Japan and the U.S. in 1987. In the past 20 years there have been 40 publications on PIM of copper or bronze, with about the same number of conference presentations. Listed in the references2–21 are some key contributions. Although there has been much progress with copper and bronze, there is no report on brass, probably because of zinc evaporation during sintering. Curiously, although fine copper and nickel powders are available that can be diffusionally homogenized during sintering, to date there has been no apparent interest in processing monel by PIM. The published literature shows that the U.S. and Japan have made equal contributions to the PIM of copper and copper alloys, accounting for 80% of the publications. The remaining 20% of the open literature comes from China, Germany, India, Singapore, Spain, and Taiwan. These publications show that molding has not been a problem and classic wax-polymer binders work well for copper. However, attaining high sintered densities and high thermal conductivities has been a challenge. The data confirm hydrogen induced swelling during sintering, often with rapid grain growth and pore separation from grain boundaries. Techniques that solve these sintering problems, such as the addition of reactive dopants (iron and titanium), usually degrade conductivity.8,11 On the other hand, high-purity powders prove most successful in achieving high thermal conductivities, but have an associated cost penalty. Because casting and machining are well established, PIM of copper struggles with a balance between issues of cost and thermal conductivity. Powders and processing cycles that deliver a high thermal conductivity are too costly compared with other manufacturing options. The PIM of copper mandates attention to oxygen control in the initial powder and via reduction during sintering. Accordingly, success in most applications is contingent on the powder and sintering characteristics. As demonstrated here, a suitable powder can be incorporated into a standard binder system to form PIM feedstock, and when processed using a straightforward sintering process, the material delivers a high thermal conductivity product. POWDERS Copper powders are produced by many processes including chemical precipitation, electrolytic deposition, oxide reduction, water atomVolume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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ization, gas atomization, and jet milling. Accordingly, copper powders are available in a wide range of particle shapes and sizes. The electrolytic and chemical powders exhibit poor packing and poor rheology in molding, so have largely been unsuccessful in PIM. 14 However, several candidate powders appear to be useful for PIM and were examined in this study. Table I characterizes the copper powders examined and Figure 1 gives representative scanning electron micrographs (SEMs). Typical purities reported by the manufacturers are ~99.85 w/o; however, our testing shows oxygen contents up to 0.76 w/o. Oxides in the particles can induce swelling during hydrogen sintering.22,23 On the other hand a surface oxide layer of 40 to 60 nm will activate sintering,24 but thicker layers inhibit sintering.

densities of the powders, where the oxide-reduced powder has the lowest solids loading (probably due to microscopic pores) and the 25 µm wateratomized powder has the highest solids loading. SINTERING High thermal and electrical conductivities in PIM products come from sintering to nearly full density while reducing oxygen and other impurities to a low level. Oxygen must be reduced early in the sintering cycle to avoid component blistering. This requires sintering in hydrogen and extraction of the oxygen impurity prior to final stage pore closure, which occurs at ~95% of the pore-free density.26 Otherwise, water vapor is generated inside the closed pores as the copper oxides react with the hydrogen sintering atmosphere. The resulting trapped water vapor increases the gas pressure in the pores, leading to pore swelling, inhibited densification, and component blistering. Trials to isolate the sintering behavior of the candidate copper powders were conducted using constant heating rate dilatometry in dry hydrogen. Examples of swelling during heating are shown in the dilatometric plot of Figure 3. The 13 µm and 16 µm water -atomized powders both swell considerably during heating, reaching a maximum dilation of about 5% at just over 700°C. Shrinkage then occurs at about the same rate as for the other powders. Oxides of these powders generate water vapor within the particles that is unable to escape as densification occurs; thus, with increasing temperature the closed pores increase pressure and cause swelling. The 15 µm

FEEDSTOCK Wax–polymer binders are generally compatible with copper powders. The PIM demonstrations to date have been based on binders such as those listed in standard references.25 In these systems wetting was facilitated by stearic acid additions. For the current experiments, a binder consisting of 55 w/o paraffin wax, 40 w/o polypropylene, and 5 w/o stearic acid (PW–PP–SA) was used. The optimal solids loading in a PIM copper feedstock depends on the morphology and packing characteristics of the powders and is easily determined using torque rheometry. 25 The optimal solids loadings of the copper powders with the PW–PP–SA binder are plotted in Figure 2. The solids loading generally correlates with the tap

TABLE I. POWDER CHARACTERISTICS Production Method

Oxide Reduced

Water Atomized

Water Atomized

Water Atomized

Water Atomized

Gas Atomized

Jet Milled

Designation

OR 11 µm

WA 13 µm

WA 15 µm

WA 16 µm

WA 25 µm

GA 8 µm

JM 8 µm

Oxygen Content (w/o)

0.332

0.223

0.758

0.151

0.326

0.379

0.214

Particle-Size Distribution D10 (mm) D50 (mm) D90 (mm)

5.9 11 17

7.8 13 23

7.3 15 24

8.4 16 36

14 25 42

4.1 8.2 13

4.7 7.9 12

Pycnometer Density (g/cm3)

8.62

8.48

8.78

8.86

8.71

8.84

8.75

Apparent Density (g/cm3) % of Pycnometer

2.8 32%

3.6 42%

3.1 35%

3.2 37%

4.5 52%

3.9 44%

3.4 39%

Tap Density (g/cm3) % of Pycnometer

3.6 42%

4.4 52%

3.8 43%

4.4 49%

5.2 60%

4.2 47%

4.3 48%

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(a)

(b)

(c)

(d)

(e)

(f)

(g)

Figure 1. Representative copper powders: (a) 11 µm oxide reduced, (b) 13 µm water atomized, (c) 15 µm water atomized, (d) 16 µm water atomized, (e) 25 µm water atomized (f) 8 µm gas atomized, and (g) 8 µm jet milled. SEM

water-atomized powder did not exhibit the same swelling behavior and performed similarly to that of gas-atomized and jet-milled powders. This gives evidence of a strong powder-vendor effect on the PIM process. Similar densification behavior is seen for the gas-atomized, jet-milled, and 15 µm water-atomized powders. No significant dimensional change takes place until the onset of shrinkage at about 680°C. The onset of shrinkage for the oxide-reduced powder is delayed until 740°C and it begins to swell at about 900°C. During heating, the reduction of copper oxides by dry hydrogen typically occurs in the range from 550°C to 680°C.27 Long hold times at temperatures in this range, or higher, can eliminate swelling by reducing the copper oxides prior to

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final stage sintering pore closure. For example, we have found that high densities can be achieved by debinding and sintering in dry hydrogen using the following thermal profile: 3°C/min to 300°C, hold for 1 h 3°C/min to 500°C, hold for 1 h 3°C/min to 600°C, hold for 1 h 5°C/min to 700°C, hold for 2 h 5°C/min to 800°C, hold for 2 h 5°C/min to 900°C, hold for 2 h 5°C/min to 1,050°C, hold for 1 h Figure 4 plots the sintered density measured on various powders using interrupted cycles after holding at 700°C, 800°C, 900°C, and 1,050°C. Sintering at 700°C produces only a slight increase Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Figure 2. Optimal solids loading for injection molding of each powder, as determined from torque rheometry

Figure 3. Dimensional change of copper powders during sintering of a heating rate of 5°C/min in hydrogen, as determined by dilatometry

Figure 4. Effect of sintering temperature on the density of the copper powders. Samples formed by low-pressure compaction (175 MPa) to fabricate small test cylinders

Figure 5. Effect of sintering temperature on oxygen content of four types of copper powder

in density over the green density. Most of the sintering densification occurs during heating at temperatures between 700°C and 900°C. The onset of pore closure varies from powder to powder. From 800°C to 900°C, the density of the gas-atomized and 15 µm water-atomized powder increases from 80% to greater than 90% of the pore-free density. Thus, for these two powders, the critical temperature range when the oxides must be reduced prior to pore closure is between 800°C and 900°C. The 15 µm water -atomized powder and the 8 µm gas-atomized powder achieved over 90% of the pore-free density at 900°C. The remaining powders have open porosity that allows for further reduction during heating to 1,050°C. At 1,050°C, the sintered densities Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

ranged from 93% to 96% of the pore-free level regardless of the powder production method or the particle size. During heating, the onset of shrinkage corresponds to the decrease in oxygen content shown in Figure 5 for the oxide-reduced, 13 µm wateratomized, gas-atomized, and jet-milled powders. Oxide reduction is rapid above 700°C, and nearly complete at 900°C. At 900°C the oxygen content is 200 ppm or less for all of the powders, except for the oxide-reduced powder which contains 400 ppm oxygen. The sintered density of the oxidereduced powder at 900°C is 85% of the pore-free level, so open porosity remains to allow for continued reduction and the escape of water vapor. The thermal profile permits oxide reduction prior to

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(a)

(b)

Figure 6. Representative optical micrographs of 13 µm water-atomized powder after pressing at 175 MPa and sintering in hydrogen at (a) 900°C for 2 h, and (b) 1,050°C for 1 h

pore closure at 900°C for the 8 µm gas-atomized powder. Representative optical micrographs of the 13 µm water -atomized powder after sintering at 900°C for 2 h and at 1,050°C for 1 h are shown in Figure 6. At 900°C, the grains are small and small pores are visible at the grain boundaries. At 1,050°C, both the grains and the pores have coarsened significantly with a slight increase in overall density. The large pores indicate that even with oxygen levels below 200 ppm at 900°C, sufficient oxygen remains to produce entrapped water vapor in the small pores and cause them to swell when heated to 1,050°C. In contrast, the microstructure of the oxide-reduced powder sintered at 1,050°C for 1 h, shown in Figure 7, con-

sists of relatively small pores, indicating little swelling from entrapped water vapor. THERMAL PROPERTIES The room-temperature thermal conductivity of copper heat sinks can be determined from the measurement of either electrical conductivity or thermal diffusivity. The electrical conductivity σ can be measured by the four-point probe method and converted to thermal conductivity λ using the Wiedemann–Franz relationship:28 λ = LσT

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V2/K2

where L is the Lorenz number for copper at 25°C), and T is the absolute temperature. The thermal diffusivity a can be measured by the laser flash method (ASTM E1461) and converted to thermal conductivity by means of the relation: λ = αCpρ

Figure 7. Representative optical micrograph of 11 µm oxide-reduced copper powder after pressing at 175 MPa and sintering in hydrogen for 1 h at 1,050°C

(1) (2.28⋅10-8

(2)

where Cp is the specific heat (0.385 J/(g·K) for copper) and ρ is the sample density. Electrical conductivity is much easier to measure than thermal diffusivity and does not depend on the geometry of the sample. Thermal diffusivity measurements require disk-shaped samples. The thermal conductivities and iron contents of several copper powders after sintering at 1,050°C are shown in Figure 8. Overall, the iron content ranged from 20 to 570 ppm. Thermal conductivities ranged from 280 W/(m⋅K) for two of the water atomized powders to 385 W/(m⋅K) for the jetmilled powder, which had the lowest iron impurity Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Figure 8. Thermal conductivity and iron content of copper powders after pressing at 175 MPa and sintering in hydrogen for 1 h at 1,050°C

level. In comparison, the thermal conductivities of commercially pure wrought copper alloys can reach 390 W/(m⋅K) for impurity levels below 50 ppm. Oxygen contents can be as high as 0.04 w/o as in the case of C11000. Commercially pure cast copper alloys have lower thermal conductivities, usually around 340–350 W/(m⋅K), because of the use of deoxidizers such as aluminum, phosphorus silicon, tin, and zinc. These elements likely comprise the majority of the 0.15 w/o of impurities typically found in commercial copper powders. Based on the Wiedemann–Franz relationship and Nordheim’s Rule,29 the predicted effect of iron impurities on the thermal conductivity of copper is plotted in Figure 9 in comparison with the experimental results. The measured values follow

Figure 10. Effect of sintering temperature on the density and electrical resistivity of PIM heat sinks

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

Figure 9. Scatter plot showing effect of iron impurity on the room-temperature thermal conductivity of copper and a comparison of our results with the model prediction

the same trend as the model predictions, but for most of the samples the measured thermal conductivities are lower than expected based solely on iron as the impurity. At low concentrations, iron may be representative of the overall impurity content, and the thermal conductivity is reduced by the cumulative effects of all the impurities. The highest iron concentration most likely results from contamination during processing. In addition to impurity effects, porosity also decreases the thermal conductivity of PIM copper heat sinks. The densities and thermal conductivities of sample PIM heat sinks are plotted as a functions of the sintering temperature in Figure 10. The thermal conductivities of the PIM heat sinks are plotted vs. porosity in Figure 11. The

Figure 11. Effect of porosity on the room-temperature thermal conductivity of copper

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pore-free density. The jet-milled copper powder had the lowest impurity level and gave the highest sintered thermal conductivity. The gas-atomized and 25 µm water-atomized powders had the highest solids loadings, which generally promotes ease of PIM processing; however, a less spherical particle shape is often preferred for component shape retention during debinding. Evaluation of the dimensional uniformity differences from these powders is a future task. Additionally, as PIM moves into thermal management applications, the obvious cost issues arise as different powders and processing options are considered. However, it is clear that the foundation in powders, processing, and design are in place to make PIM copper a successful growth area. Figure 12. Example of PIM copper heat sink. Demonstration component is approximately 20 mm wide × 20 mm long × 2.5 mm high

experimental data show slightly less dependence on porosity than predicted by the relationship proposed by Koh and Fortini,30 assuming a value of 350 W/(m⋅K) for the pore-free thermal conductivity (to take impurity effects into account). Impurity concentrations on the order of 0.1 to 0.2 w/o can be as detrimental to the thermal conductivity as 20 v/o porosity. DEMONSTRATION TRIALS Several factors determine a successful system; these include moldability as determined by torque rheometry, shape retention in sintering, ability to achieve high sintered densities and thermal conductivities, and powder cost. Demonstration component fabrication was conducted with the 13 µm water-atomized powder, mixed at a solids loading of 52 v/o with the PW–PP–SA binder. Heat-sink components approximately 20 mm wide × 20 mm long × 2.5 mm high were molded. Inspection showed that the green bodies were free of voids. After molding, the components were solvent debound to remove the wax. The remainder of the binder was burned out during heating in the sintering cycle. An example of a PIM copper heat sink fabricated by this process is shown in Figure 12. The density is 94% of the pore-free level with a thermal conductivity of 296 W/(m·K). CONCLUSIONS None of the seven copper powders tested here emerged as clearly the best choice for PIM. All of the powders achieved from 93% to 96% of the

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ACKNOWLEDGMENTS This research involved the collaborative efforts of several partners and we are especially thankful to Lye King Tan, Ravi Bollina, Pavan Suri, Justin Brezovsky, and Hoe Phong Tham for their assistance. REFERENCES 1. R. Viswanath, V. Wakharkar, A. Watwe and V. Lebonheur, “Ther mal Per for mance Challenges from Silicon to Systems”, Intel Tech. J., 2000, Q3, pp. 1–16. 2. V. Josef and L.K. Tan, “Thermal Performance of MIM Thermal-Management Device”, Powder Injection Moulding Inter., 2007, vol. 1, no. 1, pp. 59–62. 3. R.M. German and L.G. Campbell, “Atmosphere Oxidation Corrosion of Sintered Artistic Bronze”, Powder Met., 2006, vol. 49, no. 2, pp. 189–191. 4. R.M. German, S.V. Atre and J. Thomas, “Large, LowProduction Quantity Components via Polymer-Assisted Shaping and Sintering Technologies”, P/M Sci. Tech. Briefs, edited by A. Bose, Metal Powder Industries Federation, Princeton, NJ, 2002, vol. 4, no. 1, pp. 9–13. 5. T. Tonomura, “Properties of Typical Metal Injection Molded Test Parts”, Advances in Powder Metallurgy and Particulate Materials, compiled by T.G. Gasbarre and W.F. Jandeska, Metal Powder Industries Federation, Princeton, NJ, 1989, vol. 3, pp. 79–90. 6. P. F. Murley and R.M. German, “Supersolidus Sintering of Coarse Powder and its Application to Powder Injection Molding”, ibid. reference no. 5, pp. 103–120. 7. R.M. German, Powder Injection Molding, 1990, Metal Powder Industries Federation, Princeton, NJ. 8. K. Hayashi and T.W. Lim, “A Consideration on Incompleteness of Densification of Cu, Cu-Sn, and Cu-Ni Injection Molding Fine Powders by Sintering in H2 Gas”, PM into the 1990s: Proc. World Congress on Powder Metallurgy, Institute of Metals, London, UK, 1990, part 3, pp. 129–133. 9. H. Uraoka, Y. Kaneko, H. Iwasaki, Y. Kankawa and K. Saitoh, “Application of Injection Molding Process to Cu

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ABBOTT FURNACE COMPANY ________________(814) 781-7334 _____www.abbottfurnace.com ___________________21 ACE IRON & METAL CO. INC. _________________(269) 342-0185 ______________________________________________5 ACUPOWDER INTERNATIONAL, LLC _____________(908) 851-4597 ______www.acupowder.com ________________________42 AMERICAN CHEMET __________________________(847) 948-0811 ______www.chemet.com ___________________________28 ARBURG GmbH + Co KG _______________________(860) 667-6522 ______www.arburg.com ____________________________6 BLACHFORD LUBRICANTS ___________________(905) 823-9290 _____www.blachford.com _______________________15 CM FURNACES, INC.__________________________(973) 338-1625 ______www.cmfurnaces.com _______________________10 HOEGANAES CORPORATION____________________(856) 786-2574 ______www.hoeganaes.com ________INSIDE FRONT COVER INCO SPECIAL PRODUCTS _____________________(201) 848-1022 ______www.incosp.com ___________________________12 NORILSK NICKEL_____________________________(+ 7 495) 785 58 08 ___www.norilsknickel.com ______________________16 NORTH AMERICAN HÖGANÄS INC. ______________(814) 479-2003 ______www.nah.com _______________INSIDE BACK COVER OSRAM SYLVANIA____________________________(570) 268-5157 ______www.sylvania.com ___________________________8 PRINCETON ONE _____________________________(440) 243-4868 ______www.princetonone.com ______________________22 PVA MIMtech, LLC, ELNIK SYSTEMS DIVISION_____(973) 239-6066 ______www.elnik.com _____________________________14 QMP_______________________________________(734) 953-0082 ______www.qmp-powders.com _____________BACK COVER SCM METAL PRODUCTS, INC. __________________(919) 544-7996 ______www.scmmetals.com ________________________30 TIMCAL Ltd. ________________________________+41-91-873-2009 _____www.timcal.com_____________________________4 UNION PROCESS___________________________(330) 929-3034 _____www.unionprocess.com____________________54

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64

Volume 43, Issue 5, 2007 International Journal of Powder Metallurgy

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Photo Ronnie Nilsson

You buy more than metal powder – you buy knowledge!

NAH 2004/02

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RHAPSODY, Copenhagen

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Metal powders open up new possibilities for creative technical solutions. Powder components require little or no subsequent machining, achieve nearly 100% material utilization, and deliver numerous performance benefits – including the lowest total unit cost for the manufacturer. These are just some of the reasons why over 40 million powder components are produced every single day. Actually, you find more and more of them in cars, computers, household machines and electrical tools. Have the advantage on your side, contact North American Höganäs, Inc. today.

North American Höganäs Inc., 111 Höganäs Way, Hollsopple, PA 15935-6416, USA, Phone +1 8144793500, Fax +1 8144792003, www.nah.com

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