Effect of h-BN addition on the microstructure characteristics, residual stress and tribological behavior of WC-reinforced Ni-based composite coatings

Abstract

Ni-based wear-resistant coatings were prepared on substrates comprising 45 steel by laser cladding. By adjusting the proportion of hexagonal boron nitride (h-BN), the microstructure of the coating improved, and the mechanical properties of the tungsten carbide (WC)/Ni60 composite coating were optimized. The effects of the WC and h-BN powder ratio on the microstructure and properties of the cladding layer were studied by scanning electron microscopy, energy dispersive spectrometry, microhardness testing, tribometry and X-ray residual stress testing. The experimental results show that the microstructure obtained by cladding had obvious delamination. Replacing a certain proportion of WC with h-BN increased the nucleation probability of WC, transformed the slender needle-like structure into a fine granular structure, reduced the stress concentration at the needle tip, reduced the friction coefficient and improved the friction performance. At the same time, the residual stress at the interface was relieved. The optimum powder ratio was 20% h-BN + 20%WC + 60%Ni60A. Under this ratio, the microhardness of the cladding layer decreased gently along the direction of the matrix depth, forming a good gradient structure. The friction coefficient decreased to approximately 0.1, the residual tensile stress at the interface decreased to 350 MPa, and the distribution of the residual stress was relatively gentle.