Preparation process of silicide coatings on molybdenum alloy surface by molten salt method

Using Na₂B₄O₇, B₄C, NaCl, KCl, NaF, Na₂SiF₆, and Si powders as the molten salt components, the Mo–Si–B composite coatings were prepared on the surface of molybdenum alloys by the molten salt method. The influence of B content on the microstructure and oxidation resistance of the composite coatings was investigated. The results show that when the B content in the molten salt is 0.4 moL per 500 g of molten salt, the Mo–Si–B composite coatings prepared are intact, the main component is MoSi₂, and the coating thickness is 12.17 μm, exhibiting the good oxidation resistance at temperatures ranging from 800 to 1200 ℃. When the B content increases to more than 0.6 moL per 500 g of molten salt, the main component of the coatings becomes MoB. However, the Mo–Si–B composite coatings are not successfully prepared, and the antioxidant capacity of the coatings is poor. With the B content increases, the surface hardness of the coatings decreases, and the oxidation resistance of the coatings gradually declines. However, during the high-temperature oxidation at 1200 ℃, the SiO₂ phases are gradually formed on the silicides and adhered to the coating surface, hindering the oxygen transmission and enhancing the oxidation resistance of the molybdenum alloys.