Single vs. Duplex Volatilization Barrier Approach to Environmental Barrier Coatings: Plasma Spraying and Burner Rig Test Performance

SiC/SiC Ceramic Matrix Composites (CMCs) are structural materials that offer a low density and high-temperature capability in combination with high specific strength for future aero engines. SiC has excellent oxidation resistance in air, however, in water vapor-rich combustion environments, the oxidation resistance is severely compromised due to volatilization of the protective SiO₂ scale. Therefore, Environmental Barrier Coatings (EBCs) are used to protect CMCs from this environmental degradation.

In this study, steam corrosion-related degradation of Si / Yb-silicate EBC-coated SiC/SiC CMCs was evaluated by burner rig testing. The tests were conducted at a max. coating surface temperature of 1400 °C. Single (e.g. Yb₂Si₂O₇) and duplex layered (Yb₂Si₂O₇/Yb₂SiO₅) EBC topcoats were deposited using different plasma spray deposition methods namely atmospheric plasma spraying (TriplexPro), very low-pressure plasma spraying (O3CP), and suspension plasma spraying (Axial III). Due to different processing conditions and use of feedstock materials (powder and suspension), produced topcoats varied in terms of microstructure (e.g. lamellar vs. columnar structure), phase composition (Yb₂Si₂O₇/Yb₂SiO₅/Yb₂O₃ ratios) as well as amorphous content. Post-process heat treatments were applied to induce crystallization in deposited layers, which led to microstructural changes, as well. As a result, the steam corrosion resistance was affected, which will be discussed in this presentation.