Microstructure and interfacial characteristics of Ni-based composite coating on zirconium alloy substrate by laser cladding

The NiZr₂/ceramic reinforced Ni-based composite coating was in-situ synthesized by laser cladding using Ni35 self-fluxing powder on zirconium alloy substrate. The microstructure, phase constituents and interfacial characteristics were investigated by optical microscope, scanning electron microscope and X-ray diffraction method. Results indicated that the matrix of coating was mainly composed of NiZr+Ni₁₀Zr₇, fine needles NiZr₂ distributed at the top and the bottom, and blocky Zr₅(Si_xNi_1-x)₄/Zr(Si_xNi_1-x) ceramic phase in the middle of the coating. Good metallurgical bonding between substrate and coating was obtained. Heterogeneous microstructure of interface zone was mainly compromised of equiaxial NiZr phase and α-Zr at the grain boundary. The mean value of microhardness of the coating reached 1 100 HV.