Effect of WSi2 content on oxidation behavior of MoSi2-20 vol% Al2O3 composites

(Mo,W)Si2–20 vol%Al2O3 composites containing 0, 2.5, 5 and 10 mol% WSi2 were prepared by pressureless sintering at 1550 °C in H2 atmosphere, with the raw materials of ultrafine (Mo,W)Si2 and nano-sized Al2O3 powders. All of the samples underwent isothermal oxidation experiments at 1500 °C in air, and surfaces of samples were covered by an intact and dense oxide layer consisting of amorphous SiO2 and Al2O3. It was concluded that introduction of WSi2 into the MoSi2-Al2O3 composites effectively reduced oxidation losses and enhanced oxidation resistance, and meanwhile, the effect was more pronounced with the increase in addition amount. The enhanced oxidation resistance after adding WSi2 was mainly attributed to higher diffusion energy barrier of Si atoms in WSi2 than in MoSi2. Moreover, the lattice distortion initiation by the W dissolved in MoSi2 suppressed the formation of the MoO3/WO3 and promoted the generation of an intact protective oxide scale.