Effect of h-BN addition on the properties of nanostructured Al2O3–TiB2–TiN based coatings developed by combined SHS and laser surface alloying

A hard coating was obtained on AISI1025 steel substrate by the action of a high power laser beam on a powder mixture of Al, TiO2 and h-BN pre-placed on the substrate surface. The precursor powder mixture underwent self-propagating high-temperature synthesis (SHS) at the high temperatures induced by the incident laser. The products of SHS were subsequently laser alloyed onto the substrate, whereby, a hard, nanostructured coating was formed comprising of Al2O3, TiB2 and TiN. Excess h-BN in the precursor resulted in the presence of free h-BN in the coating. Microhardness and coefficient of friction (with WC-Co as counterbody) of the coating were found to reduce with increase in h-BN content in the precursor. It was possible to develop a coating with a property combination of high hardness, low wear rate and low friction coefficient.