Behaviors and Mechanism of HVOF/HVAF Sprayed WC-Co-Cr Coatings Subjected to Cavitation in Marine Environments

This study aimed to investigate the cavitation corrosion behaviors of WC-Co-Cr coatings in marine environments, with a particular focus on the relationship between corrosion and cavitation erosion. The microstructure, phase composition, element distribution, and microhardness of WC-Co-Cr coatings sprayed by both high-velocity oxy-fuel and high-velocity air-fuel were assessed. The study systematically examined the pure cavitation erosion effect, corrosion-induced cavitation erosion effect, pure corrosion effect, and cavitation erosion-induced corrosion effect on the coatings using cavitation erosion tests and electrochemical tests. Moreover, the synergistic effect between cavitation erosion and corrosion was quantitatively analyzed based on Faraday’s law. Results showed that pure cavitation erosion was the primary contributor to the damage of the coatings, followed by a significant contribution from corrosion-induced cavitation erosion. In contrast, the effects of pure corrosion and cavitation erosion-induced corrosion were negligible. The pore and lamella structure significantly influenced the cavitation erosion resistance of the coatings. Cavitation cracks were predominantly initiated at the pores and propagated along the carbide–binder interface and lamella boundary due to the mechanical effect (pure cavitation erosion). Furthermore, the propagation direction of cavitation cracks could be influenced by the corrosion effect resulting from chemical substances present in artificial seawater.