Microstructure characteristics and cavitation erosion resistance of Co-based coating fabricated via laser cladding

Marine centrifugal pumps are important mechanical equipment widely used in ships, but they are often damaged due to cavitation. In this paper, a Co-based coating was prepared on the surface of a substrate via laser cladding technology. The microstructure characteristics and phase composition of the coating were analyzed by an optical microscope (OM), a scanning electron microscope (SEM), and an x-ray diffractometer. Ultrasonic vibration cavitation tests were used to test the cavitation erosion resistance of the coating in NaCl solutions with different concentrations (0, 2.5, and 3.5 wt. %).The experimental results showed that the coating is mainly composed of γ-Co, (Co,W)6C, and Cr23C6. After 12 h of cavitation testing in different concentrations of NaCl solution, the Co-based coating exhibited better anti-cavitation performance than the 316 stainless steel substrate. The corrosion rate of the Co-based coating was significantly lower than that of the 316 stainless steel substrate. In addition, the experimental results also showed that the higher the concentration of NaCl, the faster the weight loss rate of the Co-based coating and the more pronounced the degree of surface cavitation. Although a dense oxide protective layer is easily formed on the surface of the Co-based coating and effectively inhibits the further erosion of the corrosive medium, with the increase in the concentration of NaCl solution, the erosion by chloride ions is more likely to destroy the dense protective layer and formed cavitation holes.