Research status of bond coats in environmental barrier coatings

Abstract Bond coats in environmental barrier coatings (EBCs) prevent oxidants from penetrating the substrate, mediate the mismatch of the coefficient of thermal expansion (CTE), and improve the adhesion strength between adjacent layers. However, the development of bond coats is rarely studied systematically. In this paper, the research status of the bond coats in EBCs is introduced in detail, including the materials and deposition methods. Thus far, Si, modified‐Si, mullite, etc., have been employed as bond coats. Nevertheless, visible drawbacks of each bond coat limit their application at high‐temperatures in extreme environments. Si bond coat is easily oxidized and forms thermally grown oxides that form cracks, resulting in delamination, spallation, and failure of EBCs. In the Si–HfO ₂ bond coat, the optimal ratios of Si/HfO ₂ , deposition methods, distribution of Si and HfO ₂ , and oxidation of Si remain completely unsolved. For mullite bond coat, SiO ₂ suffers selective evaporation in the water vapor environment, and the ratios of the Al ₂ O ₃ and SiO ₂ in mullite coatings restrict its service lifetime. HfSiO ₄ is a potential candidate acting as a next‐generation bond coat in EBCs is proposed. Furthermore, choosing reasonable deposition methods is beneficial to improve the performances of the bond coats in EBCs.