Oxidation Behavior of W-Si Binary Alloys

W-Si binary alloys are mainly composed of Si and W-Si compounds. During oxidation behavior of W-Si alloys, the surface of the alloy is readily oxidized, producing a dense and continuous protective film of SiO₂. It will act as a diffusion barrier and delay further diffusion of oxygen into the alloy.

F. Koch et al. investigated the effect of Si content on the oxidation resistance of W-Si binary alloys. The results showed that the oxidation rate of W-Si alloys was lower than that of pure W. The higher the Si content, the better the oxidation resistance of the alloy. Among them, WSi₁₈ alloy has the best oxidation resistance at the temperature of 600-1000°C, and its oxidation rate is 10-100 times lower than that of pure tungsten. The Arrhenius plot of oxidation rate versus 1/T shows that the oxidation activation energy of the W-Si alloy (117-136 Kj.mol^-1) is significantly higher than that of pure tungsten (80 Kj.mol^-1), which indicates that the W-Si alloy has better oxidation resistance than pure tungsten.

The researchers concluded that the large grain size is the main reason for the high surface roughness of WSi_1.7. WSi₁₃ has a smooth and dense surface structure with only a few large grains. However, the surface oxidation of the W-Si binary alloys (WSi₁₃) is more severe after 4 hours at 800°C. EDS analysis shows that the dark gray areas are mainly composed of SiO₂, which has an oxygen content of 62 at%.

However, the oxygen content in the light gray region is only 12 at%, and this region is mainly composed of SiO₂ and WO₃. Some small pits with a diameter of 10-20 μm were observed in the dark gray region, which is mainly due to the oxidation behavior of tungsten and its radial growth. the formation of WO₃ is the main reason for the volume expansion and detachment of the oxide layer. This oxidation nucleation phenomenon may be related to the presence of microscopic pores and cracks on the alloy surface and the inhomogeneous distribution of Si elements. In addition, the intermediate phase formed between W and Si reduces the strength of the alloy, which limits the application of W-Si alloys to some extent.

Reference: Fu T, Cui K, Zhang Y, et al. Oxidation protection of tungsten alloys for nuclear fusion applications: A comprehensive review[J]. Journal of Alloys and Compounds, 2021, 884: 161057.

• < Prev
• Next >