Development of a hard nano-structured multi-component ceramic coating by laser cladding

The present paper reports laser-assisted synthesis of a multi-component ceramic composite coating consisting of aluminum oxide, titanium di-boride and titanium carbide (Al2O3–TiB2–TiC). A pre-placed powder mixture of aluminum (Al), titanium oxide (TiO2) and boron carbide (B4C) was made to undergo self-propagating high-temperature synthesis (SHS) by laser triggering. Laser subsequently effected cladding of the products of SHS on the substrate. The effect of laser scanning speed on the hardness, microstructure and phase composition of the composite coating was investigated. The coating exhibited an increase in hardness and a decrease in grain size with increase in laser scanning speed. A maximum micro-hardness of 2500 HV0.025 was obtained. X-ray diffraction (XRD) of the top surface of the coating revealed the presence of aluminum oxide (Al2O3), titanium di-boride (TiB2) and titanium carbide (TiC) along with some non-stoichiometric products of the Ti–Al–B–C–O system. Field emission gun scanning electron microscopy (FESEM) and high-resolution transmission electron microscopic (HRTEM) analysis revealed some nano-structured TiB2 and Al2O3, which are discussed in detail.