Synthesis of molybdenum borides and molybdenum silicides in molten salts and their oxidation behavior in an air–water mixture

The formation of various coatings in molybdenum–boron and molybdenum–silicon systems was investigated. Boronizing and siliciding treatments were conducted in molten salts under inert gas atmosphere in the 850–1050 °C temperature range for 7 h. The presence of boride (e.g. Mo2B, MoB, Mo2B5) and silicide (MoSi2, Mo5Si3) phases, formed on the surface of Mo plates, was confirmed by X-ray diffraction analysis. The distribution of elements was determined by means of wavelength dispersive spectroscopy (WDS) spectra of the surface and line-scan analyses from surface to interior. Depending on the process type (diffusional or electrochemical) and temperature, the thickness of the protective layers formed on the substrate ranged from 6 to 40 μm. The oxidation resistance of obtained phases was investigated in an air–water mixture in the temperature range of 500–700 °C for a period up to 400 h. An improved oxidation behavior of coated plates in comparison with that of pure molybdenum was observed.