| Abstract Scope |
Calcium-magnesium-aluminosilicate (CMAS) interactions with coatings for hot section airplane structural materials are a prominent thermochemical degradation mechanism. Coating infiltration rates depend on CMAS viscosity and viscosity is influenced by CMAS composition. The ingested CMAS composition is subject to change by the engine environment and dissolution of the underlying coating. This work assesses environmental- and coating-CMAS interactions via the fifth oxide effect on CMXAS glasses (Ca30.75-Mg9-X5-Al13-Si42.25 in single cation mole percent), where X is a fifth oxide. Viscosity of CMXAS glasses was measured using a spindle-dipped viscometer, where X = Fe, Ti, Yb, Y, Gd, Zr, Hf. A critical temperature was observed in CMXAS glasses, for X = Hf, Zr additions, in which HfO2 and ZrO2 crystals precipitated, indicating there is a critical solubility limit. Computational databases including FactSage, ThermoCalc, and Giordano were used to calculate glass properties and compared to measured values to continue validating the most accurate computational model. |