Rare-earth pyrosilicate solid-solution environmental-barrier coating ceramics for resistance against attack by molten calcia–magnesia–aluminosilicate (CMAS) glass

High-temperature (1500 °C) interactions of promising environmental-barrier coating (EBC) ceramics in the rare-earth (RE) pyrosilicate system, Yb(2-x)YxSi2O7(x= 0, 0.2, 1, or 2), with three different calcia–magnesia–aluminosiliate (CMAS) glass compositions, are explored. Only the Ca/Si ratio is varied in the CMAS: 0.76, 0.44, or 0.10. Interaction between the highest Ca/Si CMAS and the EBC ceramic with the lowestx(=0, Yb2Si2O7) promotes no reaction but the formation of “blister” cracks. In contrast, the highestx(=2, Y2Si2O7) promotes the formation of an apatite reaction product, but no “blister” cracks. Observationally, it is found that a decrease in the CMAS Ca/Si ratio (0.76–0.10) and a decrease in Y-content decreases the propensity for reaction crystallization (apatite formation) and “blister” cracks. These results are rationalized based on the relative affinities between Ca2+in the CMAS and Y3+or Yb3+in the EBC ceramics, suggesting a way to tune the CMAS interactions in RE pyrosilicate solid solutions.