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Metal injection molding (MIM) is a recognized processing route for net- and near-net-shape complex parts for use in medical, automotive, industrial, and consumer industries. The MIM process holds great potential for cost reduction of orthopaedic implant devices for applications such as femoral components, tibial bases, cable crimps, and tibial trays. This study discusses the effects of processing parameters on the liquid-phase sintering behavior of injection molded ASTM F-75. Tensile test specimens were molded, debound, and sintered using different atmospheres. The static mechanical properties of the sintered alloys were compared to the cast and cast/HIP ASTM F-75. The liquid-phase sintered/solution-annealed MIM F-75 exhibited yield and tensile strengths greater than 550 and 900 MPa, respectively, with an elongation bf 17%, thus exceeding the minimum requirements of the ASTM cast F-75. The HIP'ed and heat treated MIM specimens exhibited yield and tensile strengths of 500 and 1000 MPa, respectively, with an elongation of 40%. The sintering atmosphere played a major role in determining the static mechanical properties of the alloy, which can be partly attributed to the final carbon content. The maximum as-sintered density achievable was 8.2 g/cm3. Since porosity is detrimental to the fatigue resistance, the as-sintered specimens were containerless hot isostatically pressed to eliminate any residual porosity. Rectangular test specimens were also molded, from which samples were machined in accordance with the ASTM Standard Practice for Conducting Constant Amplitude Axial Fatigue Tests of Metallic Materials (E466) to determine the fatigue properties of smooth and notched specimens. The MIM specimens performed similarly to the cast F-75, indicating a viable application of the MIM technology for F-75 implants.
metal injection molding, liquid-phase sintering, orthopaedic implants, MIMF-75
Metallurgist, Phillips Powder Metal Molding, Menomonie, WI