Effects of hot isostatic pressing and heat treatment on cast cobalt alloy

Investment cast biomedical alloys are often heat treated to refine the microstructure and improve mechanical properties. Test specimens of American Society for Testing and Materials F75 alloy (Co–28 wt-%Cr–6 wt-%Mo) were cast and solidified at two cooling rates, which influenced the size and area fraction of secondary phases (carbides) precipitated at grain boundaries and in interdendritic zones. The specimens were then subjected to hot isostatic pressing and age hardening. This produced smaller globular carbides of reduced area fraction, and reduced the size of micropores, independent of as cast characteristics. Strength and hardness were not significantly altered. The most significant effect of the post-casting treatment was to increase the ductility of the alloy, most likely due to the dissolution of brittle intergranular carbides and reduction in pore size.