Correlation of thermal conductivity of suspension plasma sprayed yttria stabilized zirconia coatings with some microstructural effects

Abstract

Yttria-stabilized zirconia (3YSZ) coatings were successfully obtained by suspension plasma spraying. The coatings present generally two-zones-microstructure comprising nanostructured zones contributed by unmolten, partially sintered nanoparticles sintered surrounded by lamellar splats formed from molten and agglomerated in-flight fine solids. In addition, different types of cracks inside the coating microstructure were classified and quantified by image analysis such as e.g. inner microcracks and segmentation cracks associated with quenching process as well as horizontal interlamellar cracks. Thermophysical properties of sprayed coatings were tested with a thermal diffusivity set up basing onto light flash principle. Subsequently, the thermal conductivity was determined with the use of literature data of density and specific heat. The calculations showed very low thermal conductivities values. The values did not correlate with coatings porosity data. Consequently, the analysis of variance (ANOVA) test allowed evaluating the possible impact of the various types of cracks on thermal conductivity. By this analysis, a good correlation between vertical cracks, which include microcracks and segmentation cracks, and thermal conductivity was found. The findings also confirmed the increase of thermal conductivity associated with this type of cracks.