Microstructure and thermal properties of inflight rare-earth doped thermal barriers prepared by suspension plasma spray

Rare-earth doped yttria-stabilized zirconia (YSZ) coatings with lower thermal conductivity have been fabricated via suspension plasma spray by dissolving rare-earth nitrates into YSZ powder-ethanol suspensions prior to plasma spraying. The effect of dopant concentration and dopant type on properties of the coatings was determined by comparing two coatings containing different concentrations of the same dopant pair (Nd2O3/Yb2O3), and three coatings having similar concentrations of different dopant pairs (Nd2O3/Yb2O3, Nd2O3/Gd2O3, and Gd2O3/Yb2O3). The porosity content of the coating was found to increase with increased total rare-earth dopant concentration but did not significantly change with dopant pairs. The cross-sectional morphology of every coating displayed a cauliflower-like structure. However, the most heavily doped coating exhibited a larger surface roughness and feathery features in the columnar structures. The thermal conductivity measurement showed that the thermal conductivity decreased with increased Nd2O3/Yb2O3 concentration. Among coatings containing different dopant pairs, the Gd2O3/Yb2O3 doped coating exhibited lowest conductivity.