Thermal cycling behavior and failure mechanism of the Si-HfO2 environmental barrier coating bond coats prepared by atmospheric plasma spraying

Abstract

In this study, HfO 2 -doped Si bond coats with four different compositions were fabricated on the SiC substrates by atmospheric plasma spray (APS) for environmental barrier coating bond coats. The result showed that relatively dense composite bond coats can be successfully deposited by the APS approach using reduced plasma power to avoid the formation of metastable hafnia phases and hafnium silicides. The thermal expansion behavior of the Si-HfO 2 bond coat was investigated. Results indicated that plasma-sprayed Si-HfO 2 bond coats showed a non-linear expansion in air environment due to the oxidation of Si and formation of HfSiO 4 . Thermal cycling behavior of the Si-HfO 2 bond coat at 1300 ℃ was also studied. The result suggested that the Si-HfO 2 bond coat with high Si concentration has relatively better thermal shock resistance, owing to its low CTE and better oxidation resistance. The HfSiO 4 formation reaction between hafnia and silica alleviate the volume contraction caused by cristobalite phase transformation. The spallation of the bond coat was attributed to the formation of thermally grown oxides (TGO) and the coefficient of thermal expansion (CTE) mismatch between the bond coat and the SiC substrate. • Four different Si-HfO 2 bond coat with different Si content were deposited on SiC substrate by APS. • Optimum mixture composition found between 20 wt% and 40 wt% Si. • The Si-HfO 2 bond coat with high HfO 2 content accelerate the oxidation of Si. • The HfSiO 4 formation reaction restrain the cristobalite phase transformation.