High Temperature Creep and Elastic Properties of Environmental Barrier Coatings

Abstract Environmental barrier coatings (EBCs) offer protection to Silicon carbide (SiC)-based ceramic matrix composites (CMCs) against corrosion, oxidation, and water vapor for high temperature gas turbine applications. EBCs are often heat-treated to crystallize the amorphous phase, to change residual stresses, or heal cracks and pores. Properties such as elastic modulus and creep resistance at high temperatures are needed to assess EBC integrity and predict EBC response in a gas turbine environment. This paper highlights new experimental methods to measure EBC elastic moduli before, during and after heat treatment using compressive load-unload cycles. Strain from compression of cylindrical EBC material was measured by digital image correlation (DIC) through a window in a resistance heated SiC element furnace. Elastic modulus was initially measured at room temperature followed by at temperature measurements between 500°C and 1200°C at various temperature intervals for increasing as well as decreasing temperature excursions to assess the change in modulus with temperature and after crystallization. In addition, creep tests of individual layers of EBC were performed under four constant compressive stress at different temperatures from 1000°C up to 1200°C for at least 24 hours. This study found an increase in EBC elastic moduli from room temperature to final HT temperature, and no change once the EBC had been fully crystallized after HT.