Predicting Thermal Stability of Advanced Thermal/Environmental Barrier Coating (T/EBC) for Gas Turbine Engines

Author(s):

Sophia R Cooper, Marcus L Young, Samir M Aouadi, Andrey Voevodin, Anindya Ghoshal, Muthuvel Murugan, and Luis Bravo Robles

Abstract:

Thermal/environmental barrier coatings (T/EBCs) are a high-temperature corrosion/oxidation-resistant solution used to improve the mechanical properties and lifespan of many high-strength bulk metals and ceramics. The recent development of high-entropy ceramics shows promising properties that prove them to be potential replacements for T/EBC applications. High entropy materials are a revolutionary group of materials known for their unique tailorable properties—specifically, to perform as T/EBCs. They also possess remarkable mechanical properties for high temperature (>1000 °C) applications. These materials exhibit high strength and fracture toughness at high temperatures compared to conventional ceramics. In this study, we performed a theoretical examination of high-entropy ceramics for high-temperature applications. We selected the coating systems based on modified Hume–Rothery “rules” for determining single-phase high-entropy materials. The Copy

Subscriptₐᵦᵧ

HfO₂₋Al₂O₃₋SiO₂ system satisfied the modified Hume–Rothery rules with values of 70.85, 2.05%, and 5.09 for the entropic, atomic size, and valence electron considerations, respectively. The metal equivalent system, Hf-Al-Si system, was also examined to better understand the HfO₂₋Al₂O₃₋SiO₂ system. Thermo-Calc CALPHAD software was used to build binary and ternary phase diagrams to determine the high-temperature stable phases of the Hf-Al-Si system, identify the phase changes that occur, and calculate the properties of the stable phases at 1300, 1350, and 1400 °C. At every temperature, the Hf-Al-Si system exhibited consistent thermal resistance values of 1.00E+20 mK/W. These are promising results for the oxide high-entropy ceramic system as a T/EBC solution.