Microstructure and high-temperature oxidation behaviour of MoSi2 protective coatings on Mo-based combustion chamber in rocket engines
Ernest Szajna, G. Moskal, Wit Stryczniewicz, Anna Kozłowska, Kamila Leśniewska‐Matys, Agnieszka B. Malinowska, Agnieszka Tomaszewska, A. Trzcionka-Szajna, Marta Mikuśkiewicz, K. Szymański
Abstract
This paper presents a detailed characterization of the microstructure and high-temperature oxidation behaviour of MoSi2 coatings obtained by pack cementation methods on a Mo-based substrate. The author focused on the challenges of applying Mo-based combustion chambers in rocket engines. Due to these assumptions, the high-temperature oxidation resistance of MoSi2 coatings was analyzed in the temperature range of 1200–1700 °C. A particular area of interest was the surface condition of MoSi2 coatings after oxidation tests, characterized by their roughness. The presented studies showed very beneficial behaviour of oxidized MoSi2 coatings from the point of view of both protective coating's morphology and durability under these conditions and the surface roughness responsible for the gas flow stability in actual working conditions. The identified microstructural phenomena related to MoSi2-based coating formation, its thermal stability and oxidation interaction were described from the thermodynamic point of view. Those analyses revealed that thermodynamically the most stable silicide compound during the first stage of coating formation is Mo5Si3, not MoSi2. It suggests that the interaction between the Si-rich gas atmosphere and the Mo5Si3 layer determines the growth progress of silicide coating. The necessary condition for further growth is an excess of active silicon sources in the reactive atmosphere in the pack cementation process.