The influence of surface roughness of sprayed zirconia coatings on laser treatment

The influence of surface roughness of plasma sprayed zirconia coatings on p ost-laser treatment was investigated, To minimize the influence from the no n-uniform laser beams obtained through the usual optics on the laser treatm ent of coatings, a conventional YAG laser gun was modified, and laser beams with a uniform intensity were obtained by installing the kaleidoscope, The melted depth of the polished coatings was approximately half that of as-re ceived coatings even when treated at the same power density (38.4 W/mm(2)) and this difference of melted depth between the as-received coatings and po lished coatings increased with the power density (47.9 W/mm(2)). In the cas e of as-sprayed coatings with a rough surface, uneven and roughly treated a reas were sharply increased in accordance with the power density. As-receiv ed coatings with surface roughness (R-a, 4.7 mum) showed an increased diffu se reflectance compared with polished coatings (R-a, 0.27 mum), and the dif ference in reflectance between the as-sprayed and polished coatings was app roximately 10% near the wavelength of the Nd/YAG laser (1016 nm). In this e xperiment, the appearance of the monoclinic phase, one of the important ind icators determining the stability of TBC coating, was not observed and non- transformable t' phase was still predominant after laser treatment. (C) 200 1 Elsevier Science B.V. All rights reserved.