Laser cladding of Ni60 alloy on 1Cr18Ni9 stainless steel: Crack suppression, micrstucture evolution, and property

Ni60 alloy is considered as a high-hardness and corrosion-resistant Ni-Cr-Si-B-C alloy for metal surface modification. In this study, crack-free coatings of Ni60 alloy were deposited on the surface of 1Cr18Ni9 stainless steel up to a thickness of 2.73 mm. The crack inhibition mechanism of Ni60 coatings and the variation of coating properties with cladding parameters were obtained through microstructure evolution and microhardness characterization. The results indicate that, the unpreheated single track samples consisted of columnar crystals with a phase composition of γ-Ni matrix and lamellar eutectic structure, and the hardness was lower than 400 HV_0.5. Upon substrate preheating, the precipitation of Cr-rich phases and changes in phase morphology lead to an increase in the microhardness by 50 HV_0.5. Thermal cycling induces the precipitation of large-sized borides and carbides in multi overlapping coatings, leading to a high cracking tendency. The combination of substrate preheating and laser power is critical for crack suppression, with lower laser power requiring higher substrate preheating temperatures. Moreover, the grain characteristics, phase composition and morphology, and microhardness of Ni60 coatings are highly sensitive to thermal input. It is noteworthy that the average microhardness of the multi overlapping coating reaches 700 HV_0.5 at a laser power of 1400 W, which is approximately 3.5 times the hardness of the 1Cr18Ni9 substrate. Simultaneously, the thickness of the heat affected zone is less than 100 μm. This study is of great significance for improving the wear resistance of stainless steel by laser cladding technology in practical applications.