Microstructures and High-Temperature Friction and Wear Behavior of High-Velocity Oxygen-Fuel-Sprayed WC-12%Co-6%Cr Coatings before and after Sealing

WC-12%Co-6%Cr coatings were deposited by high-velocity oxygen-fuel spraying technology (HVOF) on 42CrMo steel, and then, the sealing treatment was carried out by sol–gel aluminum phosphate inorganic sealing agent. The phases and porosity of the coatings before and after sealing were characterized by XRD and metallographic grayscale method, and high-temperature sliding wear tests were carried out at five different temperatures. The results showed that the coating/substrate bonding was mainly mechanical bonding with metallurgical bonding, and the high-temperature friction and wear mechanism of the coating was mainly contact fatigue and oxidation wear. The porosity of the coating was significantly reduced by aluminum phosphate sealing treatment, which was less than 2%, and the density was significantly improved. With the increase in wear temperature, the wear rate of the coatings increased, and the effect of phosphate sealing on reducing the wear loss was gradually weakened, and the highest service temperature was found near 450 °C.