Abstract

TBCs are vital thermal protection systems used in harsh environments, comprising a ceramic top coat and a metallic bond coat. The bond coat enhances adhesion between the top coat and substrate while providing oxidation and corrosion resistance at elevated temperatures. Traditionally, MCrAlX alloys have served as bond coats, where M represents Ni, Co, or NiCo, and X denotes reactive elements such as Y, Hf, Ta, or Si.
As turbine components face increasingly severe operating conditions, conventional bond coats exhibit limitations including phase instability, accelerated oxidation, and reduced durability under thermal cycling. To overcome these issues, high-entropy alloys (HEAs) have emerged as promising alternatives due to their superior thermal and chemical stability. Their multi-principal-element composition improves oxidation and corrosion resistance, optimizes diffusion behavior, and mitigates degradation mechanisms commonly observed in MCrAlX coatings.
HEAs promote the formation of a dense, continuous, and adherent thermally grown oxide (TGO) layer, minimizing spallation and enhancing coating durability. Their low oxygen permeability, stable α-Al₂O₃ formation, and resistance to phase segregation further extend service life in high-temperature applications.
This study investigates the influence of HEA compositions, with and without reactive elements—and the effect of low-temperature spray techniques such as HVOF and HVAF (M3 and i7 guns). It also examines the impact of vacuum heat treatment on bond coat behavior. Comparative analyses with conventional MCrAlX coatings highlight the advantages, challenges, and potential of HEAs as next-generation bond coats in advanced TBC systems.