Construction of a molten CMAS-resistant bilayer-structured apatite layer used for thermal barrier coatings
Lanxin Zou, Yuxian Cheng, Shijun Meng, Lei Guo
Abstract
Molten calcium–magnesium–alumina–silicate (CMAS) is easy to wet and penetrate into thermal barrier coatings (TBCs), causing the coating corrosion and premature failure. Applying a protective layer on the TBC surface is considered a useful method to alleviate CMAS attack. In this study, a bilayer-structured apatite layer was developed, on which molten CMAS has low wettability. It had an acicular upper layer and a compact lower layer, which was constructed by pre-reacting GdPO<sub>4</sub> with CMAS powders through precisely regulating the pre-reaction temperature, time and CMAS concentration. The bilayer-structured apatite layer remained microstructure integrity after heat treatment at 1250 °C for 50 h, and did not crack after 100 thermal cycles. Exposed to CMAS at 1250 °C for 20 h, the layer remained an intact structure and still had function on preventing CMAS penetration. At 1250 °C for 30 min, the CMAS contact angle on the bilayer-structured apatite layer was 17.4 °, approaching three times that on Gd<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> which is another promising CMAS-resistant TBC material. Hence, the bilayer-structured apatite layer is quite attractive for addressing the CMAS issue of TBCs.