Grain refining technique and mechanical properties of the biomedical Co-Cr-Mo alloy

Thermomechanical processes combined with reverse transformation from (ε-hcp and M₂N) dual-phase to γ-fcc phase of biomedical Co-Cr-Mo-N alloys were examined. According to XRD analysis, the reverse transformation from ε + M₂N to γ is completed after heat treating at 1223 to 1373 K without deformation, while after heat treating at 1223 and 1273 K contained residual M₂N particles in the γ matrix. After the subsequent hot compression at condition at 1273 K and strain rate less than 1 s^-1, and 1223 K and strain rate less than 10 s ^-1, ultra fine grains less than 1 μm with residual M₂NN were obtained. Therefore, it is suggested that the residual M₂NN suppressed further growing of DRXed grain. The obtained microstructure with ultra fine grain dispersed with residual M₂NN was obtained to demonstrate both grain refining strengthening and precipitation strengthening.