SiNx Coating Deposition on CoCr by Plasma-Enhanced Chemical Vapor Deposition

Cobalt chromium alloys (CoCr) are commonly used as total disc replacement components. However, there are concerns about its long-term biological effects. Coating the CoCr with a ceramic could improve the implant’s biocompatibility and wear resistance. Silicon nitride (SiNx) coatings have emerged as a recent alternative to this end. While many have evaluated physical vapour deposition (PVD) techniques to deposit these coatings, plasma-enhanced chemical vapour deposition (PECVD) may provide certain advantages. For example, it may allow for low-temperature depositions as well as more uniform coatings of complex structures. In this study, silicon nitride (SiNx) coatings with different nitrogen-to-silicon (N/Si ratio) compositions (0.65, 1.16 and 1.42) were deposited onto CoCr substrates by PECVD. It was found that the SiNx coating deposited at an NH3 flow rate of 30 sccm (i.e., N/Si ratio of 1.42), had the highest hardness and elastic modulus, 13.19 ± 1.29 GPa and 132.76 ± 9.32 GPa, respectively. While a coating roughness adequate for the application could be measured, further optimization of the coating adhesion is needed to adequately evaluate its wear properties. It was concluded that the PECVD SiNx coating deposited at an NH3 flow rate of 30 sccm showed the highest potential for the intended application.