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 (σ0.2%PS) and ultimate tensile strength (σUTS) 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 σ0.2%PS. σUTS. T. E., and reduction of area (R. A.): for the 0.06C alloy 1174±125MPa, 1549 ±23 MPa, 10 ±1%, and 36 ±5%; for the 0.12C alloy. 1223±57MPa, 1623±23MPa, 12±2%, and 44±4%, respectively. In the 45% cold-drawn 0.12C alloy, M6C carbide precipitates were observed in the dislocation network, which was caused by cold drawing. M6C 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 ε- or σ-phase was observed. As annealing temperature increased, the σ0.2%PS and σUTS 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. © 2008 The Japan Institute of Metals.