Effect of post-heat treatment on microstructure and performance of HVOF-sprayed WC–CrC–Ni hard coatings

Thermally sprayed WC–CrC–Ni cermet coatings produced by High-Velocity Oxy-Fuel (HVOF) spraying are widely used in applications requiring wear and corrosion resistance, such as hydraulic pistons, shafts, and bearings. However, their microstructural and functional integrity can be significantly altered when exposed to elevated temperatures during service or post-processing. This study investigates the effect of isothermal post-heat treatment at 300, 600, and 800 °C on a WC–CrC–Ni HVOF coating, evaluating microstructure, phase evolution, carbide-retention index (CRI), hardness, wear, and corrosion behaviour. Heat treatment at 300 °C induced stress relaxation without phase transformation. At 600 °C, partial WC decarburisation and splat densification produced the highest hardness; however, wear resistance did not improve correspondingly, demonstrating that hardness alone does not govern tribological performance. The lowest wear rate was achieved at 800 °C through oxide tribofilm formation. The as-sprayed coating showed the best corrosion resistance, which deteriorated progressively with increasing temperature. The carbide-retention index (CRI) decreased from 97.5% to 92.5% across the heat-treatment range, confirming systematic but moderate carbide degradation.