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

摘要

Thermodynamic analysis was carried out to predict the phase composition of a perhydridopolysilazane-type polymer derived ceramic coating on Mo_5SiB_2 matrix particles after heat treatment. The most probable chemical reactions between these constituents and resulting phases were calculated. The feasibility of PHPS/Mo_5SiB_2 chemical reactions was proved experimentally. An amorphous SiO_xN_y 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 Mo_5SiB_2 particles, which was found to be as twice as high at 800°C and 1100°Cin air, compared to the unprotected plain Mo_5SiB_2 phase. The oxidation of the free silicon provided by the PHPS conversion was addressed as an oxygen trap.