Effect of Alloying Elements on Microstructure of Biomedical Co-Cr-Mo F75 Alloy

Abstract

Precipitates in biomedical Co-Cr-Mo cast alloys are closely related to their wear and mechanical properties. It is important to elucidate the effects of addition of alloying elements listed in ASTM F75 on precipitation and dissolution in order to control microstructural changes in fabricating biomedical Co-Cr-Mo alloy implants. In this study, Si and Mn were selected as the alloying elements. The chemical compositions of two cast alloys were Co-28Cr-6Mo-0.25C with containing 1mass% Si dan Mn. The alloys were solution treated at temperatures at 1448 to 1548 K for holding time of 1.8-43.2 ks, followed by water quenching. The precipitates in the as-cast alloy with Si addition were M23C6 carbide, h-phase (M6C-M12C type carbide) and p-phase (M2T3X type carbide with a b-Mn structure), while M23C6 carbide and h-phase were detected in the as-cast alloy with Mn addition. The alloy with Si addition required longer solution treatment time for complete precipitate dissolution as compared with the alloy with Mn addition. The phase and morphology of precipitates observed during solution treatment depended on the heat treatment temperature and holding time and alloy composition.