The Significance of Technical Papers in Ultra Fine's Industry

Technical papers serve as a cornerstone in the dissemination of advanced research and innovative practices within the metal industry. At Ultra Fine, these documents provide critical insights into the evolving landscape of metallurgical technology and its applications.

By accessing our curated collection of technical papers, industry professionals and researchers can gain a deeper understanding of the challenges and solutions that define our field. These papers not only highlight Ultra Fine’s expertise but also foster collaboration and inspire new developments.

Links to these valuable resources are made readily available to ensure that our stakeholders are equipped with the knowledge necessary to drive progress and maintain competitive advantage in a rapidly advancing industry.

Download Technical Insights

Delve into a wealth of knowledge with our comprehensive collection of technical papers below.

Technical Papers

Technology Trends

Steels

Corrosion Resistant Medical Instruments Produced by Metal Injection Molding

J.L. Johnson

Medical Device Materials, S. Shrivastava (ed.), ASM International, Materials Park, OH, 2004, pp. 408-413.

Abstract

Medical instruments are generally produced from stainless steels because of their strength, hardness, corrosion resistance, and ease of sterilization. New instrument applications are trending toward smaller, more complex devices for minimally invasive surgery. Such devices are being designed for greater freedom of movement, which has increased the numbers of metal parts used in the assembly. Metal injection molding (MIM) is being increasingly utilized to reduce the manufacturing costs of these types of components. Common grades of MIM stainless steel include 304L, 316L, 430, 440C, and 630. Each of these materials is mixed with a thermoplastic binder and injection molded, debound, and thermally processed. The tensile properties, hardness, surface finish, and corrosion resistance of the sintered components are shown to be comparable to the specifications for their wrought and cast counterparts.

 

Conclusions

MIM can produce stainless steels with mechanical and corrosion properties that are useful for medical instruments. Austentic 316L stainless steel produced via MIM has corrosion resistance comparable to wrought 316L. Hardness values over 50 HRC can be achieved with MIM 440C for excellent wear resistance. MIM 630 provides a good combination of strength, hardness, and corrosion resistance. Besides making manufacturing of current medical devices more affordable, the MIM process can enable the cost effective production of novel designs, including microsized and functionally graded devices. Such developments may enable new solutions to current health care problems.

Bi-Metal Injection Molding of Tough/Wear-Resistant Components

J.L. Johnson, L.K. Tan, R. Bollina, P. Suri and R.M. German

Advances in Powder Metallurgy and Particulate Materials, R. Lawcock and M. Wright (eds.), MPIF, Princeton, NJ, 2003, pp. 8.234-8.244.

Abstract

Bi-material components can be processed by MIM by two-color injection molding and co-sintering, but compositions and sintering cycles must be optimized to minimize shrinkage mismatch while providing the desired properties. The effects of sintering temperature on the sintered density, hardness, and mechanical properties of M2 tool steel and boron-containing 316L stainless steel are investigated. The compatibility of co-sintering these materials is predicted based on calculations of the thermal stress and in situ strength of the component during sintering. This prediction is verified by successful Bi-MIM processing of 316L-0.5B stainless steel/M2 tool steel components for applications that require a combination of toughness and wear resistance.

 

Conclusions

Boron additions of 0.5 wt.% enhance the sintering of 316L stainless steel such that it has similar densification behavior to M2 tool steel. Strength, density, and hardness after sintering 316L-0.5B at 1245°C are all improved in comparison to 316L sintered at 1330°C. Ductility is reduced to 15%, but this is still acceptable for many applications. M2 sintered at 1245°C shows high strength and can achieve a hardness of 59 HRC after heat treating. The hoop stresses generated during co-sintering of M2 and 316L0.5B concentric rings do not exceed the in situ strengths of the materials, allowing for the fabrication of demonstration Bi-MIM components with a unique combination of wear resistance and toughness.

Design Guidelines for Processing Bi-Material Components via Powder Injection Molding

J.L. Johnson, L.K. Tan, P. Suri and R.M. German

JOM, vol. 55, no. 10, 2003, pp. 30-34.

Abstract

Powder injection molding can be used to fabricate bi-material components that provide unique functionality, such as a combination of toughness and wear resistance. Successful processing of these components requires minimization of internal stresses during sintering. The stresses generated during co-sintering of concentric rings are analyzed, compared to the materials’ strengths, and correlated with defects. The results provide guidelines for determining the compatibility of various materials and the effect of component geometry.

 

Conclusions

Successful processing of bi-material components requires that the interfacial strength exceed the maximum radial stress and that the in situ material strength exceed the maximum tensile hoop stress. These requirements can be met if the following conditions exist.

  1. Metallurgical bonding between materials Using materials with similar compositions and powder characteristics can ensure good bonding. Small modifications (less than 25%) to the powder can be used to tailor properties. This ease of modifying compositions is one of the main advantages of using PIM technology in producing metallic parts.
  2. Shrinkage match between the two materials Co-sintering materials requires that they have similar densification behavior. Minor chemistry changes can significantly alter a material’s shrinkage behavior, making it more compatible for co-sintering. Shrinkage can also be adjusted by modifying the solids loading of the feedstock.
  3. Component geometry that minimizes internal stresses Performing stress calculations on a component can identify potential design changes to reduce the likelihood of cracking. Some design changes may not affect the external dimensions of the part, making them relatively easy to implement.

Cobalt-based Alloys

Processing of MIM Co-28Cr-6Mo

J.L. Johnson and L.K. Tan

Advances in Powder Metallurgy and Particulate Materials, C. Ruas and T.A Tomlin (eds.), MPIF, Princeton, NJ, 2005, pp. 4.13-4.21

Abstract

A prealloyed Co-28Cr-6Mo powder is injection molded. Debinding and sintering are conducted in different atmospheres to evaluate their effects on the sintering response and carbon, nitrogen, and oxygen contents. Hardness, tensile strengths, and ductility are measured after hot isostatic pressing and solution heat treating. The results are correlated to the interstitial content and microstructure. Nitrogen in the sintering atmosphere increases the yield strength and hardness. The mechanical properties exceed the requirements for cast material and are comparable to those of wrought material.

 

Conclusions

Water-atomized Co-28Cr-6Mo can be injection molded and sintered to a closed pore condition in vacuum and in hydrogen, nitrogen, and hydrogen/nitrogen atmospheres. Carbon levels are typically 0.02 wt.% or less. Nitrogen in the sintering atmosphere results in nitrogenization, which compensates for low carbon levels and increases the yield strength and hardness. Solution heat treating is needed to keep the nitrogen from segregating to the grain boundaries. The static mechanical properties of HIPed and heat treated Co-28Cr-6Mo with 0.23-0.25 wt.% nitrogen exceed all ASTM F75 requirements for cast Co-28Cr6Mo. Impurities, such as Mn and Si, in the powder can lead to inclusions in the final microstructure, which may hinder fatigue properties.

Metal Injection Molding of Co-28Cr-6Mo

J.L. Johnson and D.F. Heaney

Medical Device Materials III, R. Venugopalan and M. Wu (eds.), ASM International, Materials Park, OH, 2006, p. 99-103.

Abstract

Metal injection molding of gas- and water-atomized Co-28Cr-6Mo powders is evaluated. Sintering is conducted in different atmospheres to evaluate their effects on sintering response and carbon, nitrogen, and oxygen contents. The effects of hot isostatic pressing and heat treat on the mechanical properties are investigated. Properties are correlated to the interstitial content and microstructure. Optimized processing gives mechanical properties that exceed ASTM requirements for cast and wrought Co-28Cr6Mo.

 

Conclusions

Both water-atomized and gas-atomized Co-28Cr-6Mo powders can be injection molded and sintered to a closed pore condition. Sintering in a nitrogen or a hydrogen/nitrogen atmosphere results in nitrogenization, which can compensate for low carbon levels and increase the strength. Static mechanical properties of as-sintered Co-28Cr-6Mo exceed ASTM F75 requirements for cast material. Mechanical properties exceeding ASTM F1537 requirements for wrought material can be achieved after HIP of the water-atomized powder, and after HIP and heat treat of the gas-atomized powder. Solution heat treating keeps the nitrogen from segregating to the grain boundaries, but has a mixed effect on mechanical properties depending on the powder source. Impurities, such as manganese and silicon, in the water-atomized powder produce inclusions in the final microstructure, which may hinder fatigue properties.

Technical Presentations

Comparison of Copper Powders for Metal Injection Molding

 J.L. Johnson

MIM 2021 Conference, February 22-25, 2021

Abstract

Copper powders are evaluated for their suitability for metal injection molding of high thermal conductivity heat sinks. Particle sizes, packing densities, mixing torques, impurity contents, and sintering behavior of gas-atomized, water-atomized, oxide-reduced, and jet-milled copper powders are compared. Gas atomized powders provide the highest packing densities and solids loadings. Trapped oxides can cause swelling during sintering, especially for water-atomized powders. Sintered densities of 93 to 96% of theoretical can be achieved for all of the powders with slow heating to 900°C to allow complete oxide reduction. Control of impurities is key in achieving high electrical and thermal conductivities.

Copper-based Alloys

Fabrication of Heat Transfer Devices by Metal Injection Molding

J.L. Johnson and L.K. Tan

Published in the proceedings of PM2004, EPMA, Vienna, Austria (October 17-21).

Abstract

Processing of high thermal conductivity materials, such as Al, Cu, W-Cu, and Mo-Cu by metal injection molding is reviewed. The effects of impurities, especially oxygen and iron, on the sintered density and the thermal conductivity of copper are investigated. Recently, the ability to fabricate combinations of two different materials to obtain unique functionality has been developed. In this paper, this method is used to produce a high density, high conductivity copper casing surrounding a porous copper wick to directly fabricate a heat pipe with complex geometry. The porosity and pore size distribution of the wick are measured and compared to literature values for commercial heat pipes.

 

Conclusions

Oxide-reduced, water-atomized, gas-atomized, and jet-milled Cu powders all give densities near 95% of theoretical at 1050°C. Particle size has little effect on sintered density at this temperature. Oxide reduction is practically complete by 900°C. Thermal conductivity drops significantly with as little as 50 ppm iron. Copper heat pipes can be produced by bi-material metal injection molding and co-sintering a 150/+325 mesh Cu powder with a -13 µm Cu powder. The permeability of the wick is comparable to those of commercial heat pipes.

Evaluation of Copper Powders for Processing Heat Sinks by Metal Injection Molding

J.L. Johnson, L.K. Tan, R. Bollina, P. Suri and R.M. German

Powder Metall. vol. 48, no. 2, 2005, pp. 123-128.

Abstract

Powder characteristics that enable metal injection molding of high conductivity copper heat sinks are investigated. Gas-atomized, water-atomized, oxide-reduced, and jet-milled copper powders are characterized in terms of particle size, packing density, mixing torque, and impurity content. The sintering kinetics and rate of oxide reduction are investigated using die pressed samples. Densities of 93 to 96% of theoretical can be achieved for all of the powders. Oxide reduction is complete by about 900°C. One of the water-atomized copper powders is injection molded to produce a demonstration heat sink. Thermal and electrical conductivities are measured and related to iron content and porosity. Overall impurity contents for typical powders are about 0.15 wt.%, resulting in thermal conductivities of 280 to 320 W/(m⋅K) for MIM copper.

 

Conclusions

Oxide-reduced, water-atomized, gas-atomized, and jet-milled copper powders can all be processed to give densities near 95% of theoretical with slow heating rates in hydrogen and sufficient holds for oxide reduction. Higher green densities and higher heating rates lead to swelling especially for water-atomized powders. Reduction of copper oxides occurs primarily between 700 and 900°C and has an activation energy of about 100 kJ/mol. Pore swelling can still hinder achieving densities above 95% of theoretical, even if oxygen levels are reduced to less than 200 ppm before pore closure.

Impurities are a main factor affecting electrical and thermal conductivity. The thermal conductivity dropped significantly for powders that contained 50 ppm or more iron. The iron content is likely representative of the concentration of other impurities. Typical thermal conductivities as determined by both thermal diffusivity and electrical resistivity measurements were in the 280-320 W/(m⋅K) range. Elimination of the remaining porosity is estimated to give a thermal conductivity of 350 W/(m⋅K), which is typical of commercially pure cast copper alloys containing small amounts of silicon, tin, zinc, aluminum, and phosphorus.

Metal Powder Injection Molding of Copper and Copper Alloys with a Focus on Microelectronic Heat Dissipation

R.M. German and J.L. Johnson

Inter. J. of Powder Metall., vol. 43, no. 5, 2007, pp. 55-63.

Abstract

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.

 

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 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.

Metal Injection Molding (MIM) of Thermal Management Materials in Electronics

J.L. Johnson

Handbook of Metal Injection Molding, Second Edition, D.F. Heaney (ed.), Woodhead Publishing, Duxford, UK, 2019, pp. 461-498.

Abstract

This chapter begins with an overview of heat dissipation in electronics and the need for thermal management materials. Methods of measuring thermal properties are reviewed. The characteristics and preparation of suitable powders for MIM Cu, W–Cu, and Mo–Cu are discussed. Examples of binders and mixing techniques for preparing injection molding feedstock from these powders are described. Specific issues with molding Cu, W–Cu, and Mo–Cu feedstocks into heat sink components are discussed. Processing conditions for debinding and sintering or infiltrating such components are described with a special focus on densification and control of the oxygen content, microstructure, and dimensions. Factors affecting the thermal properties, such as impurities and porosity, are discussed. Examples of MIM heat sink components are provided.

 

Conclusions

High thermal conductivity materials, Cu, W–Cu, and Mo–Cu can be processed by metal injection molding. Copper can be solid-state sintered to near full density, but care is needed to avoid hydrogen swelling. Near full density can be achieved for W–Cu and Mo–Cu by either liquid-phase sintering or infiltration. The commercial availability of composite W–Cu powders with excellent sintering behavior makes liquid-phase sintering preferable for W–Cu. Because of the poor molding characteristics of fine Mo powders and their poor densification during liquid-phase sintering, infiltration techniques are recommended for Mo–Cu. With proper powder selection and good control of sintering cycles and impurities, thermal properties close to model predictions can be achieved. Metal injection molding allows fabrication of heat sink geometries that are difficult to produce with other metal-working technologies. Novel structures, such as a heat pipe with a high conductivity casing surrounding a porous wick, can be directly fabricated into complex shapes.

Nickel Based Alloys

Metal Injection Molding of Commercially Pure Nickel for the Chemical Processing Industry

J.L. Johnson and E.J. Westcot

Inter. J. of Powder Metall., vol. 39, no. 8, 2003, pp. 37-45.

Abstract

Commercially pure Ni is used in the chemical processing industry for components that are subjected to reducing aqueous conditions. A spherical -10 µm Ni powder was evaluated for its suitability to produce such components by metal injection molding (MIM). This powder was mixed with a polymer-wax binder. Both tensile bars and rectangular bars were injection molded. Sintering optimization of debound tensile bars resulted in high sintered densities and mechanical properties comparable to commercially pure Ni alloy Ni270. For comparison in corrosion tests, 316L stainless steel rectangular bars were injection molded from a gas atomized -22 µm powder. Corrosion testing of both MIM Ni and MIM 316L rectangular bars was performed in a variety of media, including nitric acid, hydrochloric acid, bleach, sodium hydroxide, sulfuric acid, and ferric chloride solution. The results show that MIM Ni is better suited for reducing corrosive environments, such as sodium hydroxide and intermediate strength sulfuric acid, than MIM 316L, which is analogous to their wrought behavior.

 

Conclusions

Metal injection molding can be used to process commercially pure Ni with mechanical and corrosion properties comparable with handbook values. A spherical Ni powder with a particle size less than 10 µm provides the required combination of rheological behavior and sintering response to achieve these properties with metal injection molding. The general corrosion resistance of commercially pure MIM Ni is significantly better than that of MIM 316L stainless steel in 40% sodium hydroxide and 50% sulfuric acid. Thus, MIM Ni is more suitable for certain applications in the chemical processing industry.

Mechanical Properties and Corrosion Resistance of MIM Ni-Based Superalloys

J.L. Johnson, L.K. Tan, R. Bollina, P. Suri and R.M. German

Advances in Powder Metallurgy and Particulate Materials, R.A. Chernenkoff and W.B. James (eds.), MPIF, Princeton, NJ, 2004, pp. 4.89-4.101.

Abstract

Superalloys based on nickel exhibit a combination of strength and resistance to surface degradation that make them useful for many applications. Metal injection molding (MIM) of HX, 718, and 625 is evaluated. Sintering conditions for these alloys are optimized to achieve maximum density and their microstructures are characterized. 718 and 625 achieve high sintered densities via supersolidus liquid phase sintering, but pore-grain boundary break-away occurs for HX before liquid forms so lower sintered densities are achieved. The mechanical properties of MIM 718 and 625 are compared to cast, wrought, and previously reported MIM properties. The corrosion resistance of these materials is tested in various media and compared to 316L stainless steel and commercially pure Ni. While these two materials perform well under oxidizing and reducing conditions respectively, the superalloys, especially 625, perform well in both types of corrosive environments.

 

Conclusions

Achieving high densities with 718 and 625 requires sintering at or just above the solidus temperature. For the HX powders investigated in this study, sintered densities are limited by the lack of a liquid phase up to a temperature at which pore-grain boundary separation occurs. Powder chemistry is a key factor affecting liquid phase formation and the processing window for sintering to high density and optimal mechanical properties. MIM can produce alloys with a range of Ni contents to tailor corrosion properties for specific applications. MIM 316L has good corrosion resistance to oxidizing environments such as nitric acid and bleach, but MIM 270 is better suited to reducing environments such as sodium hydroxide and dilute solutions of sulfuric acid. MIM 718 is suitable for both oxidizing media such as nitric acid and reducing media such as sodium hydroxide, but performs poorly in hydrochloric acid and sulfuric acid where MIM HX performs better. MIM 625 has excellent resistance to all of these corrosive media.

Trends for 2021

Powder quality will continue to improve to meet the increasing requirements of metal additive manufacturing. Methods of producing gas atomized powders with narrower particle size distributions, greater sphericity, fewer satellites, and less internal porosity will improve throughput, mechanical properties, and overall process consistency. New alloys custom designed for laser and electron beam powder bed fusion techniques will enable better control of melt pool formation and solidification leading to finer microstructures and further improving properties. Ultra Fine Specialty Products is developing capabilities to produce pilot quantities of new gas atomized powders that can be transitioned to high volume production after successful evaluation.

Trends for 2022

Ultra Fine Specialty Products continues to expand its production of highly spherical, gas atomized powders in a wide array of alloys used in metal additive manufacturing and metal injection molding. This year, Ultra Fine has also installed capabilities to produce pilot quantities of gas atomized powders, which will enable the development of custom alloys for powder bed fusion and binder jet printing. The pilot equipment will also enable development of technology to narrow particle size distributions, improve sphericity, and reduce satellites. Upon successful evaluation, quantities can be readily scaled to high volumes on existing production equipment.

Trends for 2023

Ultra Fine Specialty Products is using its recently upgraded pilot atomizer to produce small batch sizes up to 500 lbs of custom gas-atomized powders, including tool steels, nickel-based superalloys, cobalt-based alloys, copper-based alloys, and ferromagnetic alloys for MIM and metal AM applications. Its inert gas and vacuum melt capabilities enable tight control of oxygen and nitrogen levels. Additional technologies are being installed to better control particle size distributions, improve sphericity, and reduce satellites. Upon successful evaluation, quantities can be readily scaled to high volumes on existing production equipment. Novamet/Ultra Fine is also developing post-atomization processes to further control powder flowability for specific applications.

Trends for 2024

As the numbers and types of metal AM printers continue to grow, manufacturers and operators are increasingly realizing the need for powders that are specifically customized for each machine’s printing technology. Ultra Fine Specialty Products has worked with many metal AM customers to develop a new line of powders optimized to improve the quality and speed of printing, particularly for binder jet technology (BJT) and laser beam powder bed fusion (PBFLB). These products work because of Ultra Fine’s unique atomization technology, ability to make blends from optimal cuts of powder, and additional post-atomization processes to optimize density and flowability. The new product line includes stainless steel, nickel-based superalloy, F-75, and copper powders.

Customers are increasingly requesting tight control of specific elements, including carbon, oxygen, and nitrogen, which can be achieved with Ultra Fine’s inert gas and vacuum melt capabilities. Ultra Fine continues to use its pilot atomizer to produce small batches of custom alloys with specific compositions. Upon successful evaluation, new materials based on iron, nickel, cobalt, and copper can be readily scaled to high volume production heats.

Industry Resources

Curated Links to Technical Resources and Industry Connections

Contact Us

Ultra Fine Specialty Products, LLC
500 Park East Drive
Woonsocket, RI 02895

(401) 488-4990 Office

Monday thru Friday
8:00am - 4:30pm