Oxidation Behaviour of AlCrFeNiSi-Based High Entropy Alloy Bond Coat Designed with the CALPHAD Approach

High-entropy alloy (HEA) coatings have demonstrated significant potential for high-temperature applications, outperforming conventional bond-coat materials like thermal-sprayed NiCoCrAlY used in Thermal Barrier Coatings (TBCs). Key properties including oxidation resistance, phase formation, and mechanical behaviour are highly dependent on the specific elemental composition of the HEA, where careful selection and balance of alloying elements are crucial to achieving optimal performance. However, the vast compositional space of HEAs presents challenges in optimizing ideal compositions. Calphad-based computational approach offers a powerful method to streamline this process. In this study, equilibrium and non-equilibrium (Scheil) solidification phase diagrams were simulated to identify an optimized AlxCrFeNiSiy HEA composition aimed at promoting simple solid-solution phases while minimizing undesirable intermetallics. The selected composition was synthesized via gas atomization and subsequently deposited on additively manufactured Ni-based superalloy substrates using the high-velocity oxygen fuel (HVOF) process. A TBC system incorporating AlxCrFeNiSiy HEA as a bond-coat and YSZ top-coat was fabricated. The coating's isothermal oxidation resistance was evaluated at 1100°C, assessing its suitability as a bond-coat material in TBCs. Furthermore, the microstructure, mechanical properties and phase composition of the coatings were analyzed and compared with simulation predictions, providing valuable insights into the material's performance and potential for future oxidation resistant materials.