Low temperature in-situ formation of oxygen barriers by heat treatment of aluminum infiltrated environmental barrier coatings

Environmental barrier coatings (EBCs) with great oxidation-resistant performance in steam are needed for efficient protection of silicon carbide-based composites in future advanced gas turbine engines. Besides a dense structure without rapid penetration paths for oxidants and other corrosives, refractory components such as alumina oxide or oxide-containing compounds also help to repel oxygen through coatings, which can ensure a long service life of EBC when used to infiltrate and block pores. However, due to their melting temperature up to nearly 2000 degrees C, melting and infiltration will damage EBC and matrix. In this work, metallic aluminum first infiltrates into open pores and microcracks at a low temperature of 750 degrees C, forming a dense structure, and then reacts in situ to form the refractory phases during heat treatment at 1100 degrees C, which is far below the melting point of refractory components of nearly 2000 degrees C. The results demonstrate that the structure remained dense after heat treatment. An intermedia layer composed of alumina and ytterbium aluminum garnet was observed due to the diffusion and reaction of oxygen and aluminum. The dense and refractory diffusion-reaction layer prevents the rapid infiltration and diffusion of oxidants in the engine environment to coating and matrix.