Effect of CrN Layer Composition on the Microstructure, Mechanical and Tribological Properties of TiN/CrN Multilayer Coatings

With increasingly stringent requirements for wear resistance and reliability of functional coatings for heavily loaded friction units, a relevant challenge in materials science is to establish the relationships between the parameters of reactive pulsed magnetron sputtering and the tribo-mechanical properties of TiN/CrN multilayer systems. In this study, TiN/CrN multilayer coatings were deposited by reactive pulsed magnetron sputtering using separate titanium and chromium targets. The effect of the nitrogen flow rate (0.20–0.36 L/h) during chromium sputtering on the structure, phase composition, and mechanical and tribological properties of the coatings was investigated at a fixed nitrogen flow rate of 0.08 L/h for titanium. SEM, EDS, and XRD showed that increasing the nitrogen flow rate leads to a non-monotonic change in coating thickness (2.0–2.6 µm), caused by the transition of the chromium target from the metallic to the poisoned sputtering mode. At low N2 flow rates, a subnitride Cr2N phase forms in the structure, whereas at the optimal flow rate of 0.32 L/h the coating consists of stable TiN, CrN, and (Cr0.5Ti0.5)N phases. The coating nanohardness was 20–23 GPa and the Young’s modulus was 250–300 GPa. The best tribological performance was achieved at a nitrogen flow rate of 0.32 L/h, coefficient of friction μ ≈ 0.5 and a minimum wear rate of 1 × 10−5 mm3/(m·N), which correlates with the highest H3/E2 value. It is shown that independent control of the CrN layer stoichiometry using separate targets can affect the tribo-mechanical properties of the TiN/CrN multilayer system.