Quantifying the efficiency of reactions between silicate melts and rare earth aluminate-zirconate T/EBC materials

The durability of thermal and environmental barrier coatings (T/EBCs) exposed to molten calcium magnesium aluminosilicate (CMAS) deposits depends on the nature of reactions between the coatings and deposits. These reactions consume the melt, and the crystallization products can block porosity that otherwise facilitates melt infiltration. The ideal reactions rapidly crystallize the melt with a small amount of dissolved T/EBC. This work compares the relative efficiency of reaction products reported in the literature to those formed on four prospective T/EBC materials based on multi-phase combinations of Gd- or Y-zirconates with GdAlO3, YAlO3, Gd4Al2O9, or Y4Al2O9. The results show that adding the aluminates to the zirconate materials promotes Gd- or Y-based aluminosilicates garnet and cuspidine crystallization, in addition to apatite. These phases effectively crystallize the melt, but the reaction efficiency is reduced compared to reactions with single phase zirconates. The implications for integration of these multiphase materials into T/EBC architectures are discussed.