Effects of heat treatment and hot forging on microstructure and mechanical properties of Co-Cr-Mo alloy for surgical implants

The effects of heat treatment and hot forging on the microstructure and mechanical properties of Co-Cr-Mo alloy for implant applications were examined. In an alloy annealed at 1200 degrees C for 1 h, M23C6 carbides precipitated along the grain boundary in the gamma phase matrix containing a small amount of 6 phase. The 0.2% proof strength (sigma(0.2%PS)), ultimate tensile strength (CUTS), total elongation (T. E.), and reduction of area (R. A.) of annealed alloy were 553 +/- 2 MPa, 928 +/- 41 MPa, 21 +/- 2%, and 15 +/- 1%, respectively. The sigma(0.2%PS) and sigma(UTS) of the Co-Cr-Mo alloy hot-forged at a starting temperature of 1100 degrees C increased linearly with an increase in reduction in area, whereas T. E. gradually decreased with an increase in the reduction. The sigma(0.2%PS), sigma(UTS), T. E., and R. A. of 57% hot-forged alloy were 715 +/- 86MPa, 1109 +/- 61 MPa, 8 +/- 1%, and 10 +/- 1%, respectively. In the 57% hot-forged Co-Cr-Mo alloy, a large amount of M23C6 carbide and a small amount of M6C carbide were observed in the gamma phase matrix containing the E phase. In the light of these results, it appears that hot forging with a starting temperature of approximately 1100 degrees C provided excellent mechanical properties to the alloys.