Microstructure and Properties of Boride Coating on Surface of316 Stainless Steel by Plasma Cladding

The boride coating was prepared on the surface of 316 stainless steel substrate by plasma cladding technique with self-made Mo-Fe-B-Cr flux-cored wire as raw materials. The microstructure, hardness, wear resistance and corrosion resistance of the coating were studied. The results show that a good metallurgical bond was formed between boride coating and substrate. There was a gradient layer with thickness of about 100 μm in the coating, and element diffusion occurred in the gradient layer. The massive hard phases of Mo₂FeB₂ and (Mo,Fe,Cr)₃B₂ in the coating was wrapped by the γ-Fe bonding phase, while there were a lot of reticulated eutectic structures of (Fe,Cr)₂B and (Fe,Cr)₂₃(C,B)₆ among the bonding phase with dendritic distribution. The maximum microhardness of the coating was 757 HV,which was about 3.4 times higher than that of the substrate. The wear mass loss of the coating was less than that of the substrate, and the coating had excellent wear resistance. The wear mechanism was micro-cutting of binding phase resulting in brittle spalling of hard phase particles and the formation of abrasive wear. The free corrosion potential of the coating in 5wt% NaCl solution was slightly higher than that of the substrate, and the free corrosion current density was less than that of the substrate, indicating that the coating had good corrosion resistance.