CMAS corrosion behavior of dual-phase composite Gd2Si2O7/Sc2Si2O7 as a promising EBC material

Environmental barrier coatings (EBCs) applied to gas-turbine components require excellent corrosion resistance to molten siliceous debris such as sand or volcanic ash in high-temperature environments while maintaining mechanical integrity. To date, most research has focused on single-phase rare-earth (RE) disilicates as candidate EBC materials, but here we report the superior corrosion resistance of a dual-phase disilicate composite, namely Gd2Si2O7/Sc2Si2O7 (70/30 vol%). EBSD measurements of cross-sections of the EBC after exposure to a calcium magnesium alumino-silicate (CMAS) for 0.5, 2, 12, and 48 h at 1400 °C reveal that, unlike in single-phase systems, the CMAS reaction layer consists of two distinct sublayers. The inner sublayer consists of a mixture of Ca2Gd8(SiO4)6O2 and Sc2Si2O7 crystals in a Ca-depleted glassy matrix, whereas the thinner outer region contains larger, elongated Ca2Gd8(SiO4)6O2 crystals oriented perpendicular to the composite surface and devoid of any Sc2Si2O7 crystals. The total thickness of the reaction layer is found to be about 20% less compared to that of single-phase Gd2Si2O7 under the same conditions, indicating that dual-phase RE-disilicate composites are a promising materials system for increasing the lifetime performance of EBCs.