Abstract

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 dis-ilicides 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.