Study of tribo-mechanical properties of laser clad Al2O3-TiB2-TiN-BN‖Ti-6Al-4 V alloy

Abstract

Low wear resistance and high coefficient of friction of the Ti-6Al-4 V alloy surface limits its application in situations requiring tribological participation of the alloy. In the present study, a laser clad layer, formed by laser melting of a preplaced powder mixture (Al, TiO2, TiB2, TiN, and h-BN), had been applied on the Ti-6Al-4 V alloy substrate surface to improve its mechanical and tribological properties. The microstructure, phase composition, hardness, wear properties, and scratch-resistance of the coatings were analyzed using a scanning electron microscope (SEM), X-ray diffraction (XRD), Vickers micro-hardness test, ball-on-disk wear test, and scratch indentation test, respectively. A multi-objective optimization technique was implemented to solve a multi-objective optimization problem for the determination of preferred powder composition and optimum process parameters. The optimization result showed that higher values of coating thickness and higher degree of uniformity in microstructure were obtained in the case of laser cladding carried out at a higher value of laser power-to-scan speed ratio. The formation of ceramic phases such as TiB2 and TiN reinforced with Al2O3 particles helped increase the hardness and wear resistance by four fold and two fold, respectively. The presence of partially reacted h-BN particles in the Ti-rich coating matrix helped reduce the friction coefficient by a factor of two-third. Hence, the composite ceramic coating of Al2O3-TiB2-TiN-BN on Ti-6Al-4 V alloy may be considered suitable for tribo-mechanical applications.