Thermal shock resistance of tri‐layer Yb 2 SiO 5 /Yb 2 Si 2 O 7 /Si coating for SiC and SiC‐matrix composites

Abstract A new tri‐layer Yb 2 SiO 5 /Yb 2 Si 2 O 7 /Si coating was fabricated on SiC, C/SiC, and SiC/SiC substrates, respectively, using atmospheric plasma spray (APS) technique. All coated samples were subjected to thermal shock test at 1350°C. The evolution of phase composition and microstructure and thermo‐mechanical properties of those samples before and after thermal shock test were characterized. Results showed that adhesion between all the 3 layers and substrates appeared good. After thermal shock tests, through microcracks which penetrated the Yb 2 SiO 5 top layer were mostly halted at the Yb 2 SiO 5 ‐Yb 2 Si 2 O 7 interface and no thermal growth oxide (TGO) was formed after 40‐50 quenching cycles, implying the excellent crack propagation resistance of the environmental barrier coating (EBC) system. Transmission electron microscopy analysis confirmed that twinnings and dislocations were the main mechanisms of plastic deformation of the Yb 2 Si 2 O 7 coating, which might have positive effects on crack propagation resistance. The thermal shock behaviors were clarified based on thermal stresses combined with thermal expansion behaviors and elastic modulus analysis. This study provides a strategy for designing EBC systems with excellent crack propagation resistance.