Structural and Mechanical Properties Analysis of Si/Mullite/BSAS Environmental Barrier Coatings Exposed to Thermal Cycling in Water Vapour Environment

The ongoing development of environmental barrier coatings (EBCs) offers the prospect to implement the full potential of silicon-based ceramics for high temperature structural applications. The current state-of-the-art EBC system comprises a Si bond coat, a mullite (3Al₂O₃·2SiO₂) interlayer and a (1-x)BaO·xSrO·Al₂O₃·2SiO₂, 0 ≤ x ≤ 1 (BSAS) crack-resistant and water vapour attack resistant top coat. In this study, the influence of water vapour corrosion on the structural and mechanical properties of plasma-sprayed Si/Mullite/BSAS architectures was assessed by furnace thermal cycle testing (e.g., 100 cycles, 2h/cycle at 1300°C). Commercially available mullite and BSAS powders were used to produce crystalline coatings by air plasma spraying. Fully crystalline mullite and celsian BSAS coatings were engineered under controlled conditions on silicon coated, sintered α-SiC Hexoloy substrates. The overall performance at high-temperature of these functionally graded EBCs is discussed and correlated to their microstructural characteristics.