Exceptional balance of strength and ductility in biomedical Co-Cr-W-Ni alloy with added carbon

This study investigated the effects of carbon addition on the mechanical properties and microstructural evolution of biomedical Co-20Cr-15W-10Ni (mass%, CCWN) alloys during plastic deformation. CCWN alloys with carbon contents of 0, 0.05, 0.10, and 0.20mass% were prepared in an induction melting furnace. The as-cast alloys were solution-treated at 1523 K for 7.2 ks, followed by cold swaging and heat treatment at 1323-1523 K for 0.3 ks. The most noteworthy finding was the exceptional balance between strength and ductility exhibited by the alloy with 0.20mass% carbon. This was attributed to an increased stacking fault energy through carbon addition, providing stability to the gamma(fcc)-phase even up to fracture and likely facilitating dislocation slip. Furthermore, grain refinement was a substantial contributor to the overall strength enhancement, surpassing the impact of carbide precipitation and solid -solution strengthening of carbon. Despite exceeding the carbon content outlined in the ASTM F90 standard, the alloy with 0.20mass% carbon was concluded to be suitable for the next generation of balloon-expandable stents, exhibiting a balance between strength and ductility.