Effects of Heat Treatment and Hot Forging on Microstructure and Mechanical Properties of Co-Cr-Mo Alloy for Surgical Implants

Abstract

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 � C for 1 h, M23C6 carbides precipitated along the grain boundary in thephase matrix containing a small amount of phase. The 0.2% proof strength (� 0.2%PS), ultimate tensile strength (� UTS), 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 � 0.2%PS andUTS of the Co-Cr-Mo alloy hot- forged at a starting temperature of 1100 � C increased linearly with an increase in reduction in area, whereas T. E. gradually decreased with an increase in the reduction. The � 0.2%PS, � UTS, T. E., and R. A. of 57% hot-forged alloy were 715 � 86 MPa, 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 thephase matrix containing the phase. In the light of these results, it appears that hot forging with a starting temperature of approximately 1100 � C provided excellent mechanical properties to the alloys. (doi:10.2320/matertrans.MRA2007274)