Melting and Crystallization of Silicate Systems Relevant to Thermal Barrier Coating Damage

The melting and crystallization behaviors of model calcium-magnesium-alumino-silicate (CMAS) compositions relevant to the degradation of thermal barrier coatings (TBCs) were investigated. A primary goal was to establish a baseline for studies on CMAS reactions with TBC materials, reported separately, and their potential to mitigate degradation. Ternary calcium alumino-silicate (CAS) compositions investigated melt below their equilibrium solidus owing to their metastable phase constitution. Additions of MgO or FeOx have significant effects on the melting behavior, depending on the C:A:S proportions. Amorphization on cooling is commonplace, with MgO, AlO1.5, and especially FeOx promoting crystallization. The behaviors of amorphous and crystalline versions of the same CMAS are different and depend on heating/ cooling rates, with attendant implications for their interaction with TBCs.