Effect of different brazing temperatures on Ni-based tungsten carbide coatings prepared by vacuum brazing using flexible metal cloth as brazing filler metal

Abstract:

A flexible Ni-based tungsten carbide metal cloth, which prepared by mixing WC powder, NiCrBSi powder and the binder, was coated on the surface of Q235 steel by vacuum brazing. It enables the repair of internal and curved surfaces of components. The effect of different brazing temperatures on the microstructure, shear strength, microhardness and wear resistance of coatings were explored. The results showed that the increasing brazing temperature did not change the microstructure composition of the coating. The interface of Ni-based tungsten carbide coating and steel substrate was mainly composed of Fe solid solution, Ni₃B, Ni₃Si compounds while the brazing seam zone was mainly composed of Ni solid solution, WC, W₂C, CrB and Cr₇C₃ compounds. With the increasing of the brazing temperature, the porosity rate and its average area of the coating gradually decreased, finally the microhardness and wear resistance of the coating enhanced. It was mainly attributed to the fact that after the flexible Ni-based tungsten carbide metal cloth melting, the NiCrBSi molten liquid improved the wetting of WC particles and filled the gap among WC particles with the increase of brazing temperature, and the coating had quite high microhardness and wear resistance. The bonding strength between Ni-based tungsten carbide coating and steel substrate increased first and then decreased with the increase of brazing temperature. When the brazing temperature was 1080 ℃, the bonding strength of the coating was the maximum of 336.5MPa. It was because the thickness of the coating/steel substrate interface compounds layer increased from 4.7 μm to 9.2 μm when the brazing temperature increased 1080℃, and the compound layer with appropriate thickness increased the bonding strength between the coating and the substrate. However, the thickness of the interface compounds layer increased to 13.9 μm when the brazing temperature increased to 1140℃, and the compounds layer with the excessive thickness led to a decrease in the bonding strength of the coating.