Abstract
The use of silicon-based ceramics in power generation applications is limited by recession of the passivating SiO2 when it reacts with water-vapor to form a volatile hydroxide. Environmental barrier coatings are used to prevent diffusion of reactive species to the structural ceramic substrate. Often these barriers are multilayered and/or multiphase to provide optimal thermal expansion match, microstructural stability, as well as low diffusivities. High energy X-rays are used to assess internal stress as well as phase content and stability in two coating systems: alloyed Ta2O5 for Si3N4 and strontium-aluminosilicates for SiC/SiC. In particular, the role of phase transitions and precipitation on the coating internal stresses is evaluated along with their ramifications for coating lifetime.
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