Heat treatment tailoring of microstructure and properties of laser cladding carbide reinforced nickel based coatings

A Ni35-WC-MoS₂-CeO₂ self-lubricating anti-wear coating was prepared by laser cladding, and the effects of heat treatment on the phase composition, microstructure, microhardness, residual stress, and wear properties of the coating were analyzed, the wear mechanisms of the coating were revealed. The results showed that the laser cladding coating was of good quality without obvious pores and cracks. The coating had a dense metallurgical bond with the substrate. The phase compositions were γ-(Fe, Ni), Cr₇C₃, M₇C₃, MoS₂ and CrS lubrication phase, etc. The microstructure was mainly columnar and equiaxial crystals, and the bulk hard phase and spherical lubrication phase were contained in the matrix, and the average microhardness was 904 HV, and the residual tensile stress on the surface was 304.6 MPa. The friction coefficient and wear rate of the laser cladding coating were 0.51 and 3.64 × 10⁻⁴ mm³/(N∙m), and the wear mechanisms were abrasive wear and fatigue wear, respectively. After heat treatment at 300 ℃ and 600 ℃, no phase transformation occurred in the coating, but the solid solution and carbide decomposition occurred, and the grains grew and showed the phenomenon of decomposition, which led to a decrease in the microhardness and the magnitude of residual tensile stress. After the heat treatment, the wear rate was reduced, and the friction process was more stable. The wear mechanisms were changed to adhesive wear and abrasive wear. Therefore, the heat treatment of the laser cladded self-lubricating coating could make the microstructure more uniform and release the residual thermal stresse. The hard phase of carbides was not easily peeled off from the coating, so that the coatings maintained high hardness and toughness, could help to improve the friction and wear performance.