Fracture characteristics of rare-earth phosphate and silicate environmental barrier coatings under molten CMAS corrosion

The fracture characteristics of rare-earth phosphate (LuPO₄) and silicate (Lu₂SiO₅) environmental barrier coating (EBC) materials under molten calcium-magnesium aluminosilicate (CMAS) corrosion are analyzed. EBCs are crucial for protecting SiC-based ceramic matrix composite components in the hot section of gas turbine engines. Recently the rare-earth phosphates as EBC materials have shown better performance than third-generation rare-earth silicates under CMAS corrosion. However, the fracture of EBCs under CMAS corrosion during service remains a significant concern. This work investigates the fracture characteristics of LuPO₄ and Lu₂SiO₅ using a combined experimental and computational approach. The computational model uses experimental micrographs and material properties obtained from fabricated EBC samples for fracture simulations. The simulation results are compared with experimental fracture toughness data and validated using statistical tests (p < 0.01). The results show significant degradation in fracture strength of EBC materials caused by CMAS penetration. EBC materials lost more than 40% of their initial fracture strength even at low penetration levels of 3% by volume. Simulation results show that LuPO₄ degraded more than Lu₂SiO₅. However, experimental observations from CMAS reaction tests demonstrate that LuPO₄ may exhibit higher fracture resistance than Lu₂SiO₅ under similar CMAS corrosion conditions due to the formation of dense and thick passivation reaction layer. The insights gained from this study could be used to design EBCs with improved fracture resistance under CMAS corrosion.