Effect of graphene and niobium carbide on microstructure and mechanical properties of Ni60 composite coatings prepared by laser cladding

Niobium carbide (NbC) is often used as a reinforcing phase to improve the mechanical properties of composite coatings, but its low thermal conductivity makes the flow of molten pool poor, and the cladding layer is prone to defects such as non-fusion and slag inclusion. Therefore, in this paper, Ni60–NbC composite coatings with different NbC content were prepared by laser cladding technology, and the 10 vol% graphene-20 vol% NbC-70 vol% Ni60 composite coatings were prepared under the optimal NbC component. The effects of the addition of NbC and graphene on the microstructure and microhardness of the coating were systematically discussed. The results show that the microhardness of 20 vol% NbC composite coating is increased from 680.1 HV to 882.9 HV compared with Ni60 coating without NbC.The composite coating with both NbC and graphene has a microhardness of up to 1048HV, which is 18% higher than the composite coating with only 20 vol% NbC. The mechanism is that the addition of graphene promotes the formation of chromium carbide (Cr23C6, Cr7C3) and increases the fluidity of the molten pool, which causes small niobium carbide particles to dissolve and recondense to form large particles. Large niobium carbide particles and chromium carbide jointly inhibit the excessive growth of other grains. This study provides a new idea for laser cladding of nickel-based composite coatings.