Laser surface modification and characterization of air plasma sprayed alumina coatings

Abstract

Surface modification and characterization of engineering components using high energy beams is an ever expanding and innovative area of research. Laser surface modification of plasma sprayed alumina coatings were carried out for transforming metastable γ-Al₂O₃ phase predominantly present in as-sprayed coating to a thermodynamically stable α-Al₂O₃ phase. These laser treated coatings were characterized using laser based non-destructive techniques like laser Raman spectroscopy, laser scattering, photoluminescence and piezospectroscopy for quantitative evaluation of the phase transformation, surface roughness, densification and residual stress associated with the coatings. Raman spectroscopic studies indicated the restoration of α-Al₂O₃ phase and laser scattering technique was used to optimize the processing parameters to obtain superior surface finish. Photoluminescence measurements have shown a marginal decline in residual stress and significant increase in density of the laser treated coatings.