MICROSTRUCTURE EVOLUTION OF IN SITU COMPOSITE COATINGS FABRICATED BY LASER CLADDING WITH DIFFERENT POWERS

In situ reaction-synthesized TiB-reinforced titanium-matrix composite coatings were fabricated using the rapid, non-equilibrium synthesis technique of laser cladding. The Ti and B mixture was the original powders, while the Ti-matrix composite coatings enhanced with TiB were treated on a Ti-6Al-4V surface with different laser scan powers of 2.5 kW, 3.0 kW and 3.5 kW. The phase composition, microstructure evaluation, and microhardness of the cladding coatings were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness. The composite coatings mainly consist of black fishbone-shaped a-Ti dendrites and white needle-like TiB phases. The microstructure evolution from the top to the bottom of the coatings was investigated. The TiB reinforcement dispersed homogeneously in the composite coatings and a fine microstructure was obtained in a sample fabricated with a laser power of 3.0 kW. The microhardness of the cladding coatings fabricated by different powders was over 2-fold greater than that of the Ti-6Al-4V titanium alloy substrate and achieved a maxi-mum average of 792.2 HV with the laser power of 3.0 kW. The microstructures and properties of the coatings were changed by adjusting of the laser cladding power. The effects of the laser scan power on the microstructure, hardness and friction and wear properties of the laser cladding coatings were investigated and discussed.