Improvement in Metal-on-Metal Bearing of Hip Implants with Advanced Stellite Alloys

CoCrMo alloy Stellite 21 has been used as hip implant material decades. However, its limited metal-on-metal bearing has resulted in loosening in hip implants. Three advanced alloys, Stellite 720, Stellite 21 with increased 10 wt%Cr (named modified Stellite 21) and Stellite 21 with additional 0.4 ~ 0.6 wt%CrN (named nitrided Stellite 21), are proposed in this research to improve the bearing. The wear test is performed on a pin-on-disc tribometer. The corrosion tests are conducted in the simulated human body environment. The results demonstrate that the proposed alloys all exhibit better wear resistance than the conventional Stellite 21. The corrosion resistance of modified Stellite 21 is much better than that of Stellite 21 while Stellite 720 and nitrided Stellite 21 are worse than Stellite 21 in corrosion resistance. Modified Stellite 21 with combined superior wear and corrosion resistance properties is highly recommended.