The production and properties of wrought high carbon Co-Cr-Mo alloys

The medical implant market's requirement for a forged version of the normally cast only, high carbon (approximately 0.2%) variant of the Co-Cr-Mo alloy, which would combine increased wear resistance with the mechanical properties of the low carbon (approximately 0.05%) variant of Co-Cr-Mo, initiated an investigation to establish a viable manufacturing route for the high carbon variant. Initially, a single melted (vacuum induction melted) cast and forged route, and a metal spraying process were examined. Subsequently a vacuum induction melted, electroslag remelted and hot working route was developed using a number of compositional and thermo mechanical processing variants. The mechanical properties obtained on rolled and forged high carbon Co-Cr-Mo bar from 20mm to 50mm diameter were similar to those of the low carbon variant and also met the requirement of ASTM F1537-94 (warm worked). The wear resistance of the high carbon variant, measured using a pin on disc method, indicated some advantage over the low carbon variant at high applied loads.