Fundamental study of suspension plasma sprayed silicate coatings

It is predicted that the operating temperatures of next-generation aircraft engines will exceed the present critical temperatures of any of the conventional metallic materials (<1400°C). As a result, it is likely that the application of SiC/SiC ceramic matrix composites (CMC) as primary materials. When exposed to an oxidative environment, SiC forms a protective silica scale. This layer provides additional protection from problems that may occur upon oxidation. It will, however, react with the water vapor formed during the combustion process, creating gaseous silicon hydroxides that will reduce its thickness. This problem has hindered the practical realization of CMC engines in aircrafts. Consequently, environmental barrier coatings (EBCs) are required to protect CMC components from oxidative degradation and thus ensure the reliability of CMC engines. In this study, a new deposition process, namely, the suspension plasma spray (SPS) process, is proposed to form the EBC. It produces much denser coatings by feeding a suspension of particles that are a single micron in size. It was confirmed that the coating structure and composition resulting from the SPS process were largely influenced by the residence time of the suspensions in the plasma flame. Subsequently, the optimum spray conditions were examined and discussed.