Failure Mechanism Associated with the Thermally Grown Silica Scale in Environmental Barrier Coated C/SiC Composites

The barium strontium aluminosilicate and Y2Si2O7-BSAS-coated C/SiC composites were corroded in 50%H2O–50%O2 environments at 1250°C, respectively. It was found that the coated composites suddenly lost their strength as the corrosion time was up to 250 and 750 h, respectively. During the water vapor corrosion, a continuous silica scale was formed between the SiC bond coat and environmental barrier coatings, leading to the growth stress. The thickness of silica scale grew with the prolonged corrosion time, accompanied with the accumulation of growth stress in the silica scale. When the growth stress was greater than the bond strength between silica scale and SiC bond coat, the cracks would form and propagate along their interface, resulting in the spallation of EBCs, followed by the failure of the composites.