Effect of heat treatment on the thermal conductivity of plasma-sprayed thermal barrier coatings

The effect of heat treatment on the thermal conductivity of plasma-sprayed Y sub 2 O sub 3 stabilized ZrO sub 2 (YSZ) and Al sub 2 O sub 3 coatings was investigated. A heat treatment of 1300 deg C in flowing argon for 50 h was found to significantly increase the thermal conductivity of the coatings when compared to measurements in the as-sprayed condition. Transmission electron microscopy (TEM) examination of the microstructures of the coatings in the as-sprayed and heat-treated conditions revealed that sintering of microcracks at the splat interfaces was the main cause for the increase in thermal conductivity. In the YSZ coatings, complete closure of microcracks was frequently obtained. In contrast, microcrack closure in the AL sub 2 O sub 3 coatings was characterized by the isolated necking of particles across a microcrack rather than complete closure. A model for thermal conductivity in a solid containing oriented penny-shaped cracks was used to explain the observed increase in thermal conductivity after heat treatment. Substrates: Rene 95.