Improving the corrosion resistance and mechanical property of 45 steel surface by laser cladding with Ni60CuMoW alloy powder

Abstract

Laser cladding Ni60CuMoW composite coating was fabricated on 45 steel surfaces using a synchronization powder feeding technique by 6kW transverse-flow CO2 laser apparatus. The effect of laser power and tempering treatment process on corrosion resistance of the cladding coating was investigated. The microstructure and mechanical property were analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy depressive X-ray spectroscopy (EDX), microhardness tester and PS-268A electrochemical system. The XRD and EDX results show that the cladding coating is mainly composed of γ (Ni, Fe), solid solution phase (Ni, Cu), compounds Ni31Si12, Cr5B3, CrB, Ni3B, FeNi3, M23C6 (Cr23C6 or (Fe,Ni)23C6) and a small amount of WC or W2C. With the increase of laser power, corrosion resistance and microhardness of the cladding coating have been improved. Compared with the untreated substrate, the maximum corrosion potential of single-track coating in 3.5% NaCl saturated solution increased by 136.2mV, and the lowest corrosion current density decreased by two orders of magnitude. The mean microhardness of laser cladding samples increased by 5.17, 4.90 and 4.89 times, respectively. The corrosion potential of three-track coating increased by 437.6mV and corrosion current density decreased by one order of magnitude than that of single-track coating's. After tempering by 600°C heat treatment, the primary dendrite and block eutectic in composite coating became more uniform, the maximum corrosion potential increased by 45.5mV and corrosion current density also decreased significantly.