High temperature passive film on the surface of Co–Cr–Mo alloy and its tribological properties

Abstract For the artificial hip joints, passive film formed on the Co–Cr–Mo alloy acted as a highly protective barrier in the body fluid. But its stability, composition and structure always influenced the protection. In this work, passive film was obtained by high temperature treatment. The effect of passivation environment on the properties of the passive film was investigated. The film's surface roughness, micro-hardness and structure were analyzed. In order to study the tribological behavior of the passive film, pin-on-disk tribotest was carried out under bovine serum albumin (BSA) and saline solution. Results indicated the sample passivated in vacuum had friction coefficient of 0.18 under BSA solution and 0.53 under saline solution; the sample passivated in air had friction coefficient of 0.14 under BSA solution and 0.56 under saline solution. In addition, the reference sample without passivation was tested under the same condition. It showed friction of 0.22 under BSA solution and 0.45 under solution. The lubricating mechanism was attributed to BSA tribo-film absorption on the surface and high hardness passive film.