Elevated temperature wear and friction performance of WC-CoCr/Mo and WC-Co/NiCr/Mo coated Ti-6Al-4V alloy

Abstract

The effect of adding Mo to WC-based coatings on the microstructure and dry sliding wear performance at elevated temperatures is investigated. The WC-based coatings are deposited using a high-velocity oxy-fuel process on the titanium-31 substrate. The coating was characterized by microstructure, microhardness, porosity, surface roughness, density, and bond strength. The wear and friction behavior of coatings was evaluated using a ball-on disc tribometer at temperatures of 200, 400, 600, and 800 °C and loads of 20 and 30 N. SEM-EDS and an optical profilometer were utilized to evaluate the wear rate and mechanism. The microhardness and bond strength of WC-CoCr/10%Mo coating is more than that of WC-Co/20%NiCr/10%Mo coatings. The WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coatings exhibited decreasing wear rates up to 600 °C, transitioning to an increase at 800 °C. The oxide phases of CoWO4, WO3, MoO3, CoMoO4, and NiMoO4, formed at 600 °C, aid in reducing the rate of wear and friction coefficient. However, the wear rate slightly increased at 800 °C due to vigorous oxidation and softness of coatings. The friction coefficient of WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coating decreases with increasing temperatures due to the lubricating properties of oxide phases on the worn surface. The WC-CoCr/10%Mo coating demonstrates a lower friction and wear rate than the WC-CoCr and WC-Co/20%NiCr/10%Mo coating. At 200 °C, the predominant wear mechanisms were abrasive and fatigue wear, while at 800 °C, oxidative wear, abrasive wear, and adhesive wear were observed.