Microstructures and Mechanical Properties of Biomedical Co-29Cr-6Mo-0.14N Alloys Processed by Hot Rolling

The effect of hot rolling on the microstructural evolution and mechanical properties of biomedical Co-29Cr-6Mo-0.14N (mass pct) alloys has been investigated. The alloy strength increases with increasing hot-rolling reduction; the specimen hot rolled to 92.8 pct (equivalent strain of 3.04) exhibits a yield stress as high as 1100 MPa, which is twice that of the conventionally prepared specimens, with no significant loss in ductility. The grain size hardly changed after hot rolling to 60.0 pct, whereas a specimen hot rolled to 92.8 pct has finer grains. The hot-rolled specimens exhibit deformed microstructures with many deformation twins and dislocation boundaries. The accumulated strain increases monotonically with increasing hot-rolling reduction, although short annealing occurs on each hot-rolling pass. The strengthening mechanism in the hot-rolled Co-29Cr-6Mo-0.14N alloys is discussed by considering the dislocation and grain refinement strengthening.