Cyclic ablation of high-emissivity Sm-doped ZrB2/SiC coatings on alumina substrates

Samarium-doped ZrB2/SiC (ZBS) coatings possess properties of high emissivity and excellent ablation performance suitable for hypersonic applications. Of interest in the current study is how cyclic ablation affects the scale development on alumina substrates. ZBS coatings with 3, 5 and 8 mol% of samarium (Sm) dopant were prepared via shrouded plasma spray onto alumina substrates and subjected to two 60-s ablation cycles with temperatures reaching up to 1700 degrees C. Blisters were observed on the Sm-doped coatings after the 1st cycle as a result of a local eutectic reaction between the ablation products and alumina substrate. A Sm-stabilized t-ZrO2 phase was identified through X-ray diffraction after the ablation of the Sm-doped coatings. The ZBS with 5 mol% of Sm dopant produced a flower-like microstructure after the 2nd cycle due to the formation of convection cells.