High Entropy Alloy (HEA) Bond Coats for Thermal Barrier Coatings (TBCs): A Review

Abstract

 

Due to the aggressive operation conditions of turbine hot sections, protective coatings are required to provide oxidation and hot corrosion resistance for superalloy components. Thermal barrier coatings (TBCs) are a typical thermal protection system for these systems, and they are mostly made of a ceramic topcoat and metallic bond coat. Conventional bond coat materials are MCrAlX (M: Ni, Co or NiCo and X: reactive elements such as: Y, Hf, Ta, Si). Owing to its combination of strength, ductility, thermal stability, wear resistance and oxidation resistance, high-entropy alloys (HEAs) have presented promise for use as bond coat materials in high-temperature applications. Thanks to its cocktail effect, optimally chosen HEAs could help to enhance the hot corrosion resistance of bond coats, through the formation of a continuous thermally grown oxide (TGO). Moreover, HEAs could help to control the diffusion between the bonding layer and substrate in elevated temperature environments. In this work, the thermodynamic, mechanical, and microstructural behavior of HEAs will be discussed. Furthermore, the selection and usage of HEAs as bond coats will be explored and compared to conventional bond coats in TBC systems.