Microstructure and wear resistance of in situ NbC particles reinforced Ni-based alloy composite coating by laser cladding

Abstract

The in situ synthesized NbC particles reinforced Ni-based alloy composite coating was produced by laser cladding a precursor mixture of Ni-based alloy powder, graphite and niobium powders on a steel substrate. The microstructure, phase composition and wear property of the composite coating were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and dry sliding wear test. The experiment results show that the composite coating is homogeneous and free from cracks, and about 0.8 mm thick. The microstructure of the composite coating is mainly composed of NbC particles, CrB type chromium borides, γ-Ni primary dendrites, and interdendritic eutectics. CrB phases often nucleate and grow on the surface of NbC particles or in their close vicinity. NbC particles are formed via in situ reaction between niobium and graphite in the molten pool during the laser cladding process and they are commonly precipitated in three kinds of morphologies, such as quadrangle, cluster, and flower-like shape. Compared with the pure Ni-based alloy coating, the microhardness of the composite coating is increased about 38%, giving a high average hardness of HV0.21000, and the wear rate of the composite coating is decreased by about 32%, respectively. These are attributed to the presence of in situ synthesized NbC particles and their well distribution in the coating.