Internal Stresses in Ytterbium Disilicate Multilayer Environmental Barrier Coatings With Calcium-Magnesium-Aluminosilicate Exposure

The interaction of calcium-magnesium-aluminosilicate (CMAS) prototypic engine deposits with Yb₂Si₂O₇-based multilayer environmental barrier coatings was studied using a combination of high-energy synchrotron X-ray techniques in both in situ and ex situ experiments at beamline 1-ID at the Advanced Photon Source. Changes in the phase-specific stresses from ambient temperature to 1350°C were investigated with wide-angle X-ray scattering.  Small-angle X-ray scattering was used to study the interaction of CMAS with nanoporosity, while X-ray computed tomography was used to examine microstructural changes in the coating during exposure. It was found that CMAS interacts strongly with the Yb₂Si₂O₇ topcoat, leading to an increase in internal compressive stress at high temperature, and large cracks in the CMAS that extend through the Yb₂Si₂O₇ topcoat when cooled to room temperature.  Successful use of Yb₂Si₂O₇ as an environmental barrier will likely require a protective topcoat.