Effects of Laser Scanning Speed on Microstructure, Microhardness, and Corrosion Behavior of Laser Cladding Ni45 Coatings

The effects of laser scanning speed on the microstructure, microhardness, and corrosion behavior of Ni45 coatings were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness, and electrochemical measurements. The results showed that increasing laser scanning speed promotes the transformation from planar crystals to dendrites and refines the grains concurrently. The gamma-(Ni, Fe), FeNi3, and M-23(C,B)(6)are identified as the primary phase composition in the Ni45 coatings regardless of the laser scanning speed. Thereinto, the formation and growth of M-23(C,B)(6)precipitates can be inhibited with increasing laser scanning speed due to the higher cooling rate, which affects the microhardness distribution and corrosion resistance of the coating. On the one hand, the microhardness of the whole coating presents a downtrend with increasing laser scanning speed due to the reduction of M-23(C,B)(6)phase. On the other hand, the corrosion resistance in 0.5 M NaCl solution is improved to some extent at higher laser scanning speed because the less precipitation of M-23(C,B)(6)reduces the depletion of Cr around the precipitates. In contrast, all the coatings exhibit undifferentiated but poor corrosion resistance in the highly corrosive 0.5 M NaCl + 0.5 M H(2)SO(4)solution.