Design and evaluation of multilayer Yb₄Hf₃O₁₂-based T/EBCs with enhanced thermal stability for high-temperature applications

Thermal/environmental barrier coatings (T/EBCs) systems are regarded as potential solutions to address the degradation challenges of ceramic matrix composites (CMCs) under extreme temperatures in aeroengine applications. Rare-earth hafnates are recognized as promising candidates for the top-layer materials of T/EBCs. In this work, Yb₄Hf₃O₁₂/Yb₂Si₂O₇/Si and Yb₄Hf₃O₁₂/Yb₂SiO₅/Yb₂Si₂O₇/Si T/EBCs systems were designed and fabricated via plasma spraying, and their isothermal oxidation and water-quenching thermal shock behaviors at 1500 °C were systematically evaluated. The results revealed that the T/EBCs system incorporating a Yb₄Hf₃O₁₂ top layer exhibited excellent high-temperature performance and maintained its structural integrity at 1500 °C. Compared with the tri-layer system, the four-layer system demonstrated better oxidation and thermal shock resistance, which was attributed primarily to the incorporation of the Yb₂SiO₅ interlayer, which effectively enhanced the interfacial stability and mitigated the thermal expansion coefficient mismatch between adjacent layers, and reduced the stress fluctuations at the coating edges and interfaces. In a tri-layer system, the spallation of the top layer can be identified as an important failure mechanism. However, for both multilayer systems, the reduction in the Si bond layer emerged as a critical factor contributing to their high-temperature degradation.