Surface coatings for improved tribocorrosion response of biomedical stainless steel

Abstract

The performance of total hip replacements is largely determined by their propensity to degrade in vivo. Degradation occurs through complex interactions between wear and corrosion (termed tribocorrosion). The long-term durability of the articulating surfaces is an important factor for the success of prostheses. During the past few decades, significant research has been conducted into understanding such interactions to improve the triboco1rosion perfonnance of biomaterials. However, not much attention has been given to the tribocon-osion response of Physical Vapour Deposition (PVD) coatings. The need for improved tribocon-osion response of biomedical stainless steel in a biological environment was the main motivation of this project. The goal was to determine whether CrN and CrN-temary coatings on 316LVM synthesized by unbalanced magnetron sputtered Physical Vapour Deposition (PVD) result in better triboc01rosion perfonnance. Furthermore, the purpose of this work was to improve the understanding of degradation mechanisms taking place and investigate the mechanical and electrochemical contributions to material losses. Cr-Zr-N, Cr-Si-N and Cr-Al-N ternary coatings were studied and compared to a benchmark material, CrN. The coatings displayed a much higher hardness than the untreated 3 l 6L VM stainless steel and exhibited good adhesion to the substrate. The tribocorrosion investigation was earned out under different electrochemical conditions and applied nonanal loads via a reciprocating sliding tribometer configuration, rubbing against an inert counterface in Ringer's solution to mimic biological environments. A parametric study showed that the overall material loss was significantly diminished for PVD treated surfaces. The mechanical integrity of the passive film on CrN-based coatings resulted in improved resistance to wear antagonised coITosion. However, despite their good adhesion to the substrate, some coatings exhibit delamination failure under higher applied loads and anodic potential.