Effects of heat treatment on microstructure and mechanical properties of Ni60/h-BN self-lubricating anti-wear composite coatings on 304 stainless steel by laser cladding

Laser clad Ni60/h-BN self-lubricating anti-wear composite coating on 304 stainless steel were heat treated at 600 °C (stress relief annealing) for 1 h and 2 h, respectively. Effects of the phase compositions, microstructure, microhardness, nano-indentation and tribological properties of the composite coatings with and without heat treatment had been investigated systemically. Results indicated that three coatings mainly consist of the matrix γ-(Ni, Fe) solid solution, the CrB ceramic phases and the h-BN lubricating phases. The maximum microhardness of the coatings was first increased from 667.7 HV _0.5 to 765.0 HV _0.5 after heat treatment for 1 h, and then decreased to 698.3 HV _0.5 after heat treatment for 2 h. The hardness of γ-(Ni, Fe) solid solution without heat treatment and after heat treatment 1 h and 2 h were 5.09 GPa, 7.20 GPa and 3.77 GPa, respectively. Compared with the coating without heat treatment, the friction coefficients of the coating after heat treatment were decreased obviously. Effects of the heat treatment time on friction coefficient were negligible, but were significant on wear volume loss. Comparatively speaking, the laser clad self-lubricating anti-wear composite coating after heat treatment for 1 h presented the best anti-wear and friction reduction properties.