Effect of Main Arc Current on Microstructure and Cavitation Resistance of NiCrBSi-WC Alloy Coating Prepared by Plasma Transfer Arc Welding

Abstract

The effect of main arc current on the microstructure, electrochemical properties, and cavitation erosion resistance of NiCrBSi-WC alloy coating by plasma transfer arc welding was studied. The results show that the coating is composed of γ-Ni, WC, W₂C, Cr₇C₃, CrB, and FeNi₃ phases. With the decrease in main arc current, the microstructure is gradually refined, and the grain size and Schmidt factor are reduced, which are 12.62 ± 2.6 μm and 0.42, respectively. At the same time, the coating has a strong γ-Ni texture in (111) orientation. The refinement of the coating microstructure and the existence of surface passivation film slow down the electrochemical corrosion in boric acid solution and effectively improve the corrosion resistance of the coating. The increase in microhardness is due to the second phase strengthening mechanism of WC and Cr₇C₃, and the maximum value can reach 663.5 ± 6.2 HV. The damage and repair process of the passive film of the coating was studied by the synergistic method of cavitation erosion. With the increase in the main arc current, the average corrosion depth rate (MDER) of the coating can be reduced to 1.02 ± 0.03 μm/h, which is due to the improvement of the independent repair ability of the passive film, and the microhardness test results are inversely related to MDER. According to the above analysis results, the synergistic mechanism of cavitation corrosion of NiCrBSi-WC alloy coating is put forward. NiCrBSi-WC alloy coating prepared by plasma transfer arc welding technology in this study has great application prospects in the nuclear industry.