Microstructure–Thermal Conductivity Relationships for Plasma‐Sprayed Yttria‐Stabilized Zirconia Coatings

The microstructures of plasma‐sprayed yttria‐stabilized zirconia (YSZ) coatings are complex, contributing to challenges in establishing microstructure–thermal conductivity relationships. Furthermore, the dynamic evolution of microstructure and properties during service offers a significant challenge in defining design strategies and extended coating performance. In this paper, the relationship between microstructure and thermal conductivity is investigated for three sets of plasma‐sprayed YSZ coating systems prepared using different morphology powders, different particle size distributions, and controlled modification of particle states through plasma torch parameters. Both ambient and temperature‐dependent thermal conductivity were conducted in the as‐sprayed and thermally aged states. The results suggest that a range of thermal conductivities can be achieved from the coatings, offering potential for microstructural tailoring for desired performance. The results also demonstrate that different as‐deposited microstructures display varying propensity for sintering and these attributes need to be considered in the design and manufacturing cycle. This expansive study of a range of coatings has also allowed synthesis of the results through thermal conductivity–porosity maps and has allowed elucidation of the contributing microstructural components for both the ambient and high‐temperature thermal conductivity. Considering that the operating thermal transport mechanisms are different at these two temperature extremes, such mapping strategies are of value to both science and technology.