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

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 (greater than 1000 deg 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 HfO2-Al2O3-SiO2 system satisfied the modified Hume-Rothery rules with values of 70.85, 2.05 percent, 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 deg 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.