Effects of Niobium Element on Microstructure and Microhardness of Ni-based Alloy Laser Cladding Coating

Several Ni-based alloy cladding coatings with different Nb element contents were successfully fabricated on the substrate of 42CrMo steel by laser cladding technology. The effects of Nb contents on microstructure, phase composition and microhardness of the cladding coatings were investigated. The results show that the microstructure of the interface between the cladding coatings and substrate, the central part of the cladding coating and the surface of the coating were successively planar crystal, dendrite, granular isometric grains; with the increase of Nb element content, the microstructure of the cladding coatings was mainly composed of γ-Ni dendrites, interdendritic eutectics, dispersed NbC particles and a few CrBC4 type chromium borides instead of γ-Ni phase, CrB type chromium borides, M7C and M23C6 type carbides and Ni31Si12 type silicide. When Nb element content was 10wt%, the microstructure refinement was particularly significant. In addition, the microhardness of the cladding coatings gradually increased with the increase of Nb element content, When Nb element content reached 10wt%, the microhardness of the cladding coating was maximum (about 550 HV0.2), it was twice that of the Ni-based alloy cladding coating without Nb element.