An experimentally-validated computational framework for CMAS degradation of environmental barrier coatings

Conference Dates

June 24-29, 2018


The work addresses reactions between silicate deposits, generically known as CMAS, and yttrium disilicate (YDS), a candidate environmental barrier coating (EBC) for SiC/SiC composites. The primary goal is to elucidate effects of deposit composition, exposure temperature and time on the extent of YDS recession as well as the associated compositional and morphological evolution of reacting phases. Phase equilibrium calculations are used to assess deposits of twelve different compositions at 1300°C and 1400°C; experimental observations of YDS recession are reported for three of these compositions at both temperatures. The results show that recession depths reach terminal values for exposure times ≥ 100h. Terminal recession depths are sensitive to deposit composition but only weakly affected by temperature. Deposits with high initial Ca:Si ratio react most severely with YDS, forming a thick layer containing an apatite reaction product interpenetrated by residual melt. The severity of the reaction decreases with decreasing Ca:Si ratio, and is least severe for deposits with insufficient Ca:Si ratio to produce apatite.

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