Microstructure and Thermal Properties of Double Rare-Earth Co-doped SrZrO3 Coating by the Solution Precursor Plasma Spray

Double rare-earth (Yb/Gd) co-doped SrZrO3 (SZYG) coatings were prepared by solution precursor plasma spray (SPPS) using an aqueous solution precursor. The SZYG coating is characterized as two phases of SrZrO3 and t-ZrO2 with interpass boundaries structure, nano- and micrometer porosity and through-thickness vertical cracks, analyzed by x-ray diffraction (XRD) and the scanning electron microscopy. XRD results showed that SrZrO3 and t-ZrO2 are very stable after heat treatment at 1400 °C for 360 h due to the doping of rare-earth elements. By comparing the thermal cyclic durability of the SZYG single-layer and the SZYG/YSZ double-layer coatings, the thermal lifetime of the double-layer coating is 650 cycles, which is 40% longer than that of the single-layer coating. The thermal conductivity of the as-sprayed SZYG coating prepared by SPPS is 0.83 W m−1 K−1 at 1000 °C, which is ~ 34% lower than that of SrZrO3 coating prepared by SPPS (~ 1.25 W m−1 K−1, 1000 °C). The superior performance of the SZYG coating is attributed to the co-doping of Yb2O3 and Gd2O3.