Plasma sprayed 18mol% YO_1.5 stabilized hafnia as potential thermal barrier coating

Considerable efforts are being invested to explore alternative ceramic materials to yttria stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications. In this work, 18 mol% YO_1.5 stabilized HfO₂ (18YSH) is proposed as potential TBC material. Stoichiometric 18YSH was prepared by atmospheric plasma spraying. The 18YSH coating exhibits low thermal conductivity over the whole temperature range investigated and a minimum thermal conductivity of 0.832 W/m·K at 800 °C. Average hardness and Young's modulus values have been determined to be 7.01 ± 1.33 GPa and 111 ± 26.8 GPa respectively. These values are superior to those exhibited by YSZ coating. In addition, the sintering temperature of 18YSH coating is at least 100 °C higher than that of a 8 YSZ coating and thus 18YSH will be more resistant to sintering. Finally, 1) the coating reliability of 18YSH TBC has been studied by thermal cycling to 1100 °C and 2) calcium–magnesium–alumino-silicate-(CMAS)-induced degradation was investigated at 1250/1300 °C. The related failure mechanism was investigated and a model describing the CMAS degradation process is presented.