CoCrMo alloys in hip and knee replacements applications

摘要

CoCrMo alloys have been widely used in metal on metal (MoM) hip replacements. On the one hand, they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, believed to be associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the wear rate is unacceptably high. There have been several reports that the formation of a surface organic layer appears to reduce the wear rate. Equally, the formation of a high surface deformed layer has been observed, but it remains unclear whether this is a good or bad phenomena. The present work correlates the potential with surface status, the formation of the organic layer, and subsurface microstructure. Several techniques have been employed such as Tafel, EIS, SEM, FIB, and Nanoindentation to study the potential effect on wear rate. The potential has a crucial role in the surface roughness, organic layer formation, and subsurface microstructure (and consequently mechanical properties of the surface). Furthermore, it is shown that the lowest wear rate was associated with the formation of the organic layer but not associated with the highest surface hardness. The highest wear rate was due to the interaction between wear and corrosion.