Effect of Cu content on the mechanical and tribological properties of MoN-Cu coatings deposited by HiPIMS

Abstract

Using the advantages of the high ionization rate of Cu under High-Power Impulse Magnetron Sputtering (HiPIMS), the mechanical and frictional performance of MoN coatings can be further optimized. Here, MoN-Cu coatings with Cu content ranging from 1.5 to 19.3 at.% were prepared using HiPIMS and analyzed for their mechanical and frictional properties. All MoN-Cu coatings are extremely dense and smooth, and the hardness can reach 29.5 GP at 3.8 at.% Cu due to the combination of FCC-Mo₂N and δ-MoN phases. MoN-Cu coating have excellent tribological properties at room temperature (RT), but the coefficient of friction (CoF) slightly increases as the Cu content rises. The CoF and wear rate of MoN-Cu-1.5 at.% can be achieved at 0.28 and 4.5 × 10⁻⁸ mm³/(N·m) at room temperature (RT), respectively. At 400 °C, the Cu-3.8 at.% coating demonstrates superior frictional properties, attributed to the facile oxidation of δ-MoN, with a CoF of 0.34 and a wear rate of 6.4 × 10⁻⁷ mm³/(N·m). Then the CoF and wear rate of MoN-Cu coatings continue to increase with increasing Cu content. At 500 °C, due to the diffusion of Cu and tribochemical reactions, a lubricating MoCuO₄ phase formed in the wear tracks, which significantly improved the lubrication performance of the coating at higher temperatures but also increases the wear rate.