CHARACTERIZATION OF LASER GLAZED PLASMA SPRAYED YTTRIA STABILIZED ZIRCONIA COATINGS

A CO2 continuous wave laser with defocused beam was employed to glaze the surface layer of plasma sprayed 20 wt.% yttria stabilized zirconia/MCrAlY coatings on 420 stainless steel substrates. An evaluation was made of the applicability of the thermal conduction model proposed by Greenwald. Results of experiments in this study showed that the laser glazing process was capable of producing shiny surfaces of low roughness on the plasma sprayed zirconia coatings. The coupling efficiency of the laser beam with the plasma sprayed zirconia coatings was about 65% at the travel speed of 4500 mm min-1. Laser glazing increased the microhardness from about 550 Hv for the as-sprayed layer to about 1550 Hv for the as-glazed layer. There was a heat affected zone (HAZ) under the resolidified layer, and the glazed layer revealed exclusively cubic phase with columnar and columnar-dendritic structures which grew perpendicular to the surface with {100} preferred orientation.