Laser cladding NiCrBSi/TiN/h-BN self-lubricating wear resistant coating on Ti–6Al–4V surface

Abstract

Self-lubricating wear resistant composite coating with TiN0.3, TiN and TiB as reinforcement phases, BN as lubricating phase were fabricated on the surface of Ti–6Al–4V alloy substrate by laser cladding with NiCrBSi, TiN and BN composite powders. The phase compositions, microstructure, interface metallurgical bonding and interdiffusion behavior between coating and substrate, microhardness, wear profile and tribological properties are investigated by x-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron backscatter diffraction technique(EBSD), microhardness tester and multi-purpose friction and wear testing machine, respectively. And the corresponding friction and wear mechanism is analyzed. Results show that the nickel-based composite powder containing TiN reinforcing phase and BN lubricating phase reacts to a composite coating which is densely bonded with the matrix and has no obvious defects such as pores and cracks. The section of the coating is smooth and the microstructure is fine, and the reinforcement phase is uniformly distributed in the coating with distributing the reinforcement phase uniformly in the coating. TiNX and BN in the coating are mainly in the form of black particles gathered into dendritic form. When the h-BN mass fraction is 5%, the average microhardness of the coating is about 967.1 HV, which is about 2.6 times higher than that of the substrate (370 HV). The friction coefficient and wear rate of the coating are obviously lower than that of the substrate, and the wear surface of the cladding layer is relatively smooth, and the wear resistance is remarkably improved.