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 1900A degrees 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 (A similar to aEuro parts per thousand < 0.1 mu m) 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 alpha-Al2O3 and a mullite sublayer in which Al2O3 crystals are introduced into SiO2.