Advanced Stellite alloys with improved metal-on-metal bearing for hip implants

• Develop advanced Stellite alloys with improved metal-on-metal bearing.
• Increase chromium content to improve the wear resistance of Stellite 21.
• Increase chromium content to improve the corrosion resistance of Stellite 21.
• Develop advanced Stellite alloys as potential hip implant materials.

Stellite 21 is a low-carbon Co–Cr–Mo alloy that has been used for hip implants for decades. The Stellite 21 implants can fail when the femoral head and the acetabular cup loosen because of limited metal-on-metal bearing. Two modified Stellite 21 alloys with better bearing capacities are proposed as replacements in this study: Cr-modified Stellite 21 with additional 10 wt.% Cr, and N-modified Stellite 21 with addition of 0.5 wt.% CrN. The wear and corrosion resistances of these alloys were investigated in simulated conditions experienced by hip implants in human bodies. The experimental results show that the proposed alloys all exhibit better wear resistance than the conventional hip implant material, but only Cr-modified Stellite 21 displays better corrosion resistance, thus this alloy should be considered for use in future hip implants.