Surface modification of plasma sprayed Al_2O_3-40 wt% TiO_2 coatings by pulsed Nd:YAG laser melting

摘要

Plasma sprayed Al_2O_3-40 wt% TiO_2 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/cm~2 while these were eliminated when melted with in 800 kW/cm~2 power density. Predominant β-Al_2TiO_5 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.