Tribological and microstructural analysis of heat treatments on medical grade cobalt-chromium-molybdenum alloys.

Abstract

Cobalt-chromium-molybdenum (CoCrMo) is a common material for medical devices such as prosthetic joint implants due to its biocompatibility and wear and corrosion resistance. Some CoCrMo implants last for a long time in the human body, while others fail early. This discrepancy in longevity may be explained by the range of microstructures and resulting material properties that can occur in CoCrMo after different manufacturing processes. This research examines various heat treatments of CoCrMo and their resulting microstructure and properties for hip and knee implant bearing surfaces. After heat treatment, wear tests were performed using a pin on disk tribometer for two million cycles, and corrosion testing was performed using a 3-electrode cell potentiostat in bovine serum to simulate conditions in the body. Grain structure and phase composition were reviewed for each sample by using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) microscopy. From this, we could determine the grain size, orientation, and phase composition that would result in the different physical and chemical properties. This research demonstrates that the untreated forged sample showed high wear resistance and a cyclically treated sample is highly resistant to both wear and corrosion. These observations can be attributed to microstructure features such as phase content, grain size, and grain boundary misorientation angles that influence the characteristics of the implant material.