Microstructural evaluation of laser remelted gadolinium zirconate thermal barrier coatings

Abstract

Abstract Thermal barrier coatings having NiCoCrAlY bond coat and Gd2Zr2O7 top coat were produced utilizing HVOF and APS processes. Then the coatings were subjected to CO2 continuous wave laser remelting by using different laser parameters. The effect of laser remelting process on the surface roughness, microstructure, grain size, hardness and phase transformation was investigated. The microstructural characterizations showed that a smooth, flat and dense surface having a network of segmented cracks was observed and open porosities were sealed throughout with a thin (~ 35 μm) remelted layer. The surface roughness value decreased from 8.3 μm to 2.9 μm for as-sprayed and laser remelted specimens respectively. Furthermore, equiaxed and columnar grains that are perpendicular to the surface were formed and the grain sizes decreased from 7.03 μm to 3.69 μm due to laser process parameters. The hardness value increased from 10.66 GPa to 12.73 GPa with decreasing grain size. XRD patterns of as-sprayed and laser remelted top coats indicated that the structure of the coating has been changed due to preferred orientation after surface modification by laser remelting.