The Current Status of Environmental Barrier Coatings and Future Direction of Thermal Spray Process

Abstract

In the next-generation of turbine engines, improving the heat resistance and reducing the weight are the essential solutions to increasing the thermal efficiency and reducing fuel consumption and CO₂ emissions. Silicon-based ceramics (e.g., SiC_f/SiC ceramics matrix composites (CMCs) and monolithic Si₃N₄) are the leading candidates for these applications because of their extreme light weight and superior heat resistance compared to the current Ni-based alloys. The main challenge of the Si-based ceramics is oxidation and volatilization of the silica in the high-temperature combustion gas environment with the water vapor and thereby its rapid recession. The most promising approach is protecting the surface of the ceramic matrix composites from the water vapor attack by an external environmental barrier coating (EBC) layer. Since the early 1990s, a lot of efforts have been made to develop suitable EBCs; however, no single material can satisfy all the EBC requirements. Thereby, the current EBC trends are directed to the development of multilayered EBCs, with different functions as a significant solution to prevent CMC recession and to maximize its performance for next engine generation. This paper discusses the history, current status, and future trends of EBC development not only in the world but also in Japan. Furthermore, it introduces future prospects of fine particle spraying in EBC developments.

 

This Paper was Originally Published in Japanese in J. Jpn. Thermal Spray Soc. 57 (2020) 76–87.

Fig. 4 Multifunctional and multilayer coating systems: (a) a thermal barrier coating system for Ni-based superalloy substrates and (b) an environmental barrier coating system for silicon carbide composite substrates. (Created with reference to Professor Sampath’s figure). (Reprinted from Kentaro Shinoda, Jun Akedo (2018)¹²²⁾ © Surface Technology Association).