Surface modification of plasma sprayed Al2O3–40 wt% TiO2 coatings by pulsed Nd:YAG laser melting

Plasma sprayed Al2O3–40 wt% TiO2 coatings were subjected to a pulsed Nd:YAG laser melting with power densities of 640 and 800 kW/cm2 in order to minimize the surface porosity, micro-cracks, partially melted or unmelted regions, and achieving homogeneous microstructure. As-sprayed and the laser melted surface microstructure, chemical composition, microhardness and roughness were characterized by using scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Vickers hardness and profilometer. Surface morphology of a laser melted coating showed that inhomogeneities are reduced, however, network of cracks were formed irrespective of power density. Columnar growth features were observed in laser melted regions when melted with 640 kW/cm2 while these were eliminated when melted with in 800 kW/cm2 power density. Predominant β-Al2TiO5 phase was observed upon both the laser melted coatings. With an increase of laser power density, laser melted coatings exhibited considerable increase in microhardness and decrease in surface roughness due to significant reduction in the surface defects.

► Al2O3–40 wt% TiO2 coating surface was modified with pulsed Nd:YAG laser melting.
► Surface microstructure, chemical composition, microhardness and roughness examined.
► Surface homogeneity was increased with increasing the power of pulsed laser.
► Improvement in microhardness and decreases of roughness observed with high power.