Crack development behavior in thermally sprayed anti-oxidation coating under repeated thermal-oxygen coupling environment

The crack development behavior in thermally sprayed anti-oxidation coating was investigated after long-term and short-term oxidation with repeated thermal cycles from 1500 °C to room temperature. According to the distribution characteristics, the formed cracks can be divided into three types: type-A cracks with multi-directional features, type-B cracks originated from the inner interface bulges and type-C cracks initiating at surface oxide layer. Based on the analytical math models (blunt crack model and interface roughness model), the maximum stress at different positions was evaluated from the perspective of inner interface roughness, uneven oxide film, original microcracks and gathering micropores. The original vertical type-A cracks are most dangerous due to the highest crack tip stress. However, the micropore distribution or appropriate interface may promote transformation of vertical type-A cracks to less dangerous horizontal type-A cracks. This study on crack development behavior provides a fundamental insight and further avenues to optimize the composition and structure of thermally sprayed ceramic coating.