Microstructure characteristics and shear strength of wide-band laser clad Ni60 composite coatings reinforced with WC particle

Ni60/WC based composite coatings were prepared on surface of Q550 steel by using wide-band laser cladding technology. Microstructure characteristics, elemental distribution and phase constitution of composite coatings were analyzed. Shear strength tests were carried out for quantitative measurement of bonding force at coating/substrate interface, and fracture surface morphologies were investigated to analyze the failure mechanism of interfaces. Results indicated the WC particles were partially dissolved in composite coating and precipitates with complicated structure were in-situ formed. The cored-eutectic structure consistsof hard M₂₃C₆ (M represents for Cr, Fe and W) carbides inside and is surround by eutectic of M₂₃C₆ and γ-Ni matrix. The formation of planar growth and dendrites facilitated a dense metallurgical bonding on the interface. As the laser power being increased to 2.8 kW, the shear strength of composite coating is 279.8 MPa, which is 75% of that of base metal. Fracture surface analysis indicated the fracture mechanism of coating interface is a mixture of brittle fracture and ductile fracture. The bonding force of coatings made by lower power is decreased due to the WC particles get accumulated at the interface.