Microstructural evolution and wear behaviors of laser-clad Stellite 6/NbC/h-BN self-lubricating coatings

Cobalt-based self-lubricating coatings with the addition of NbC and h-BN were prepared by means of laser cladding on a die steel (Cr12MoV) substrates, aiming at their implementation in metal forming applications involving demanding friction reduction and anti-wear. The effect of different amounts of h-BN with constant content NbC (30 wt%) on the microstructure of the laser-clad Stellite 6 alloy was probed through measures of XRD, SEM, EDS and EBSD. Microhardness, wear properties, and antifriction mechanism of the self-lubricating coatings were also discussed as well. The results proved that with an increase in h-BN content, in addition to NbC phase with polygonal shape observed in the h-BN-free Stellite 6/NbC coating, Nb(C, B) interstitial compounds having multiple grain orientations were formed in inter equiaxed crystal regions. Following the microstructural characterization, the tribological behavior and micro-hardness were analyzed. The results exhibit considerably better anti-friction properties of Stellite 6/NbC/h-BN coating compared to subtract and its excellent tribological performance could be reflected by data of friction test. The lubrication effect of h-BN is proved by the reduction in coefficient of friction. Meantime, the addition of NbC helps in improving micro-hardness and anti-wear. The NbC solidification-growth was detailly discussed in the paper.