Exploring the Microstructure and CMAS Resistance of Yb₂Si₂O₇ Environmental Barrier Coatings(EBCs) Deposited by Axial and Radial Injection Plasma Spraying

Yb₂Si₂O₇ environmental barrier coatings (EBCs) were sprayed under three conditions using two plasma torches with radial and axial injection, varying torch power and plasma gas composition. The 91 kW axially injected EBC with reduced N₂ and H₂ (A1) was ~90% crystalline as-sprayed, with ~25 wt.% Yb₂SiO₅ as a secondary phase and small, uniformly distributed porosities. Increasing N₂ and H₂ by 5% (A2) improved particle melting and densified the microstructure, but resulted in an amorphous as-sprayed state with higher silicon evaporation. The 30 kW radially injected EBC (R1) was also amorphous as-sprayed, and 75 wt.% Yb₂SiO₅ was crystallized after annealing at 1300 °C for 24 hours. Under CMAS exposure at 1350 °C, R1 formed a dense apatite reaction layer, altering CMAS composition and hindering infiltration after 96 hours. The Yb₂Si₂O₇-rich EBC (A1) showed CMAS infiltration through its thickness after 72 hours but showed no blistering or damage. A2’s denser structure with minimal porosity further resisted CMAS infiltration.