Polymer derived oxidation barrier coatings for Mo-Si-B alloys

Thermodynamic analysis was carried out to predict the phase composition of a perhydridopolysilazane-type polymer derived ceramic coating on Mo5SiB2 matrix particles after heat treatment. The most probable chemical reactions between these constituents and resulting phases were calculated. The feasibility of PHPS/Mo5SiB2 chemical reactions was proved experimentally. An amorphous SiOxNy phase and free Si were found by X-ray diffraction analysis and Raman spectroscopy. The presence of these two phases explain the improvement in oxidation resistance of the Mo5SiB2 particles, which was found to be as twice as high at 800 °C and 1100 °C in air, compared to the unprotected plain Mo5SiB2 phase. The oxidation of the free silicon provided by the PHPS conversion was addressed as an oxygen trap.