Effects of carbon addition on wear mechanisms of CoCrMo metal-on-metal hip joint bearings

Abstract

The wear behaviors of biomedical CoCrMo prosthetic alloys containing various amounts of carbon were investigated using a standard hip joint simulator in a simulated body fluid. A few chunks and punctate σ-phase precipitates were observed in the low-carbon (LC) alloy; these were responsible for the abrasion and run-in wear. Increasing the carbon content led to greater precipitation of globular M₂₃C₆-type carbides. As a result, lower wear loss was observed in the high-carbon (HC) alloy. However, the Student's t-test analysis on wear loss indicated that there was no significant difference in wear loss between the LC-LC and HC-HC combinations. Surface fatigue caused by torn-off of Mo-rich carbides was the dominant wear mechanism in the HC alloy. Further, Cr-rich carbides prevent three-body abrasion and increase the wear resistance.

Keywords: Carbon addition; CoCrMo alloy; Mo-rich-carbide-induced-pitting; Wear mechanism.