Effect of cold rolling on phase decomposition in biomedical Co-29Cr-6Mo-0.2N alloy during isothermal heat treatment at 1073 K

Nitrogen addition is a promising strategy for improving the mechanical properties of biomedical Co-Cr-Mo alloys. In the present study, a Co-29Cr-6Mo-0.2N (wt.%) alloy was cold-rolled to obtain a height reduction of 30% and then isothermally heat-treated at 1073 K for up to 86.4 ks. The microstructural evolution of the alloy resulting from the metal forming and heat treatment was investigated. During heat treatment, the cold-rolled specimen exhibited phase decomposition in the mixture of ε, Cr₂N, and σ phases. However, the eutectoid ε + Cr₂N lamellae, which developed in the unrolled specimen, were hardly observed. Since the cold-rolled alloy had dislocation substructures and intergranular boundaries related to ε martensite, which formed during cold rolling, the phase decomposition was accelerated and significantly different from that of the unrolled counterpart.