In Situ High Temperature XRD Studies of Molten Natural CMAS Corrosion on Thermal Barrier Coatings

High temperature behaviors of natural calcium-magnesium-alumino-silicate (CMAS) and CMAS coated thermal barrier coating (TBC) systems (CMAS-TBC) were investigated using combined techniques of in-situ high temperature XRD-Rietveld quantitative phase analysis and elemental mapping analysis. The XRD result indicates that silicate mineral, diopside (CaMgSi2O6), is formed at temperature higher than 800 °C. At 1200 °C, CMAS is found to have penetrated into the YSZ layer resulting in chemical interaction between CMAS and YSZ. Prolonged heat treatment shows that the interaction results in the formation of zircon (ZrSiO4) and spinel (MgAl2O4). This thermochemical interaction results in the weakening of the YSZ layer, which ultimately leads to the spallation of YSZ layer during the cooling down phase of the thermal cycling.