Study on microstructure and mechanical property of a biomedical Co-20Cr-15W-10Ni alloy during multi-pass thermomechanical processing

The present work investigates the microstructural evolution of a biomedical Co-20Cr-15W-10Ni alloy during multi-pass thermomechanical processing (TMP) and clarifies its effect on the tensile properties. The results indicate that multi-pass TMP consisting of repetitive cold groove-rolling followed by annealing is attractive for fabricating the alloy rod for fine wire and mini-tube making. The multi-pass TMP provided significant grain refinement from 100 to 4 mu m via five repetition and, can create bimodal grain structures consisting of fine (approximate to 3 mu m) and coarse grains (4-16 mu m). The bimodal grain structure provided a superior strength-ductility combination, a yield strength of 593-738 MPa and ultimate strength of 1197-1304 MPa with a uniform elongation of 54.7-61.1%. Changing the annealing condition in the final TMP step enables to further refine the grains to 2 mu m and also modify the grain size distribution and, the dispersion and fraction of nano-carbides. Thus, the mechanical properties of the Co-20Cr-15W-10Ni alloy can be further optimized, leading to a yield strength of 795-890 MPa and ultimate strength of 1328-1363 MPa with a uniform elongation of 49.4-64.0%.