Investigation of microstructure of laser cladding Ni-WC layer on Al-Si alloy

A plasma-sprayed Ni-WC layer was deposited on an Al-Si cast alloy surface, and then it was further melted by a 5 kW CO₂ laser. The microstructure and chemical composition of the laser-melted zone were investigated, and the microhardness in different parts was measured. Experimental results showed that the chemical composition of the sample was not uniform. Compositional segregation in the laser-melted zone was found. Some amorphous structure appeared in the nickel-rich locations after laser melting. Owing to the thermal effect of the laser scanning, an intermediate-phase Ni₃Al segregated from this region and formed Ni₃Al grains and amorphous grains. Some WC particles melted in the matrix, and chromium carbide Cr2;|C6 and (Cr,W)C separated during the cooling process. The highest microhardness (1027HV) was found in the high-nickel region.