Molybdenum-based oxidation-resistant MoSi2–Al2O3 and WSi2–Al2O3 coatings

Various studies and comparative tests are conducted on oxidation-resistant unmodified and modified MoSi2–Al2O3 and WSi2–Al2O3 silicide coatings in air at 1800 and 1900°C. Metallographic, x-ray diffraction, electron microprobe, and chemical analyses show that the introduction of alumina into molybdenum and tungsten disilicides improves their hardness and produces fine-grained silicides with high corrosion resistance. The composition with fine alumina particles (Ø < 0.1 μm) with the total alumina concentration from 3 to 15 wt.% in the coating is most favorable for improving the oxidation resistance of disilicides. It is shown that the high oxidation resistance of MoSi2–Al2O3 and WSi2–Al2O3 coatings is due to the presence of alumina in disilicides, which contributes to the formation of an external high-temperature oxide layer. This layer consists of α-Al2O3 and a mullite sublayer in which Al2O3 crystals are introduced into SiO2.