Cavitation behavior of laser cladded cobalt-based alloy in solutions with different pH values

In this study, the microstructural characteristics, wear properties, and cavitation erosion resistance of laser-cladded cobalt-based coatings in solutions with different pH values were systematically investigated. Characterization techniques including energy dispersive spectroscopy and electron backscatter diffraction were employed to reveal the rapid solidification microstructural features of the coatings. It was confirmed that the coatings consist of three phases: (Co,W)6C/Co7W6 carbides, γ-Co solid solution, and Cr23C6/Cr7C3 carbides. Mechanical tests showed that the microhardness of the coating was 619.21 HV0.3, which was three times that of the 316 substrate, and the friction coefficient was reduced by 30%. The results of the 20 h cavitation erosion test indicated that the coating exhibited the optimal performance in a neutral environment (pH = 7), with a cumulative mass loss of 42.4 mg, and the most severe damage was observed in an alkaline environment (pH = 11), with a cumulative mass loss of 107.7 mg. In the acidic environment (pH = 3), molybdenum (Mo) element enrichment led to the formation of a MoO3 passive film, which significantly improved the corrosion resistance. Combined with chemical reaction kinetics analysis, the dissolution mechanism of the Cr2O3 oxide film under different pH conditions and the protective effect of carbide phases were clarified. This study provides a theoretical basis for the engineering application of cobalt-based alloy coatings.