Effects of Cold Drawing and Annealing on Mechanical Properties and Microstructure of Co-Cr-Mo-Ni-Fe Alloys for Surgical Implants

Abstract

The effects of cold drawing and annealing on the mechanical properties and microstructure of 0.06C and 0.12C-Co-Cr-Mo-Ni-Fe alloys were examined. The 0.2% proof strength (σ 0.2%PS ) and ultimate tensile strength (σ UTS ) of the cold-drawn 0.06C alloy increased proportionally as the reduction in area increased, whereas the total elongation (T. E.) decreased linearly. The 45% cold-drawn alloys showed the following σ 0.2%PS , σ UTS , T. E., and reduction of area (R. A.): for the 0.06C alloy 1174 ± 125 MPa, 1549 ± 23 MPa, 10 ± 1%, and 36 ± 5%; for the 0.12C alloy, 1223 ± 57 MPa, 1623 ± 23 MPa, 12 ± 2%, and 44 ± 4%, respectively. In the 45% cold-drawn 0.12C alloy, M 6 C carbide precipitates were observed in the dislocation network, which was caused by cold drawing. M 6 C carbide precipitates were also observed in the grain and grain boundary in the 0.06C and 0.12C alloys annealed from 950 to 1200°C. The matrix was the γ-phase; no e- or σ-phase was observed. As annealing temperature increased, the a σ0.2%PS and σ UTS of the annealed alloys decreased gradually, while the T. E. increased linearly. Approximately 70% T. E. was obtained by annealing at 1100°C for the 0.06C alloy, and at 1200°C for the 0.12C alloys.