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 γ(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.