Oxidation Behavior of W-Si Ternary Alloys

The W-Si ternary alloys own a longer oxidation life than W-Si binary alloys. The oxidation behavior of different ternary alloys is significantly lower compared to those of pure W and WSi13 alloys. In the temperature range of 600-1000°C, the oxidation rate of WSi₁₃Zr₁₃ alloy is only 0.16-0.27 times that of WSi₁₃ alloy. the oxidation rate of W-Si-Cr alloy is lower than that of WSi₉Y₁₃ alloy, while the oxidation rates of WSi₈Cr₁₂ and WSi₁₂Cr₇ alloys at 1000°C are only 0.25 and 0.023 times that of WSi₉Y₁₃ alloy, respectively. 0.25 and 0.023 times, respectively.

The elements Si, Cr, Ti, Zr, Nb and Y have low neutron irradiation activation and stable thermodynamic properties and are widely used to improve the oxidation resistance of refractory metal alloys. These elements can be oxidized rapidly when a reactor de-cooling accident occurs and form a dense and continuous oxide film on the surface of W-based alloys, thus retarding further oxidation of W-based alloys.

Koch et al. investigated the oxidation characteristics of W-Si ternary alloys at a temperature of 1000°C. When the WSi₁₂Cr₇ alloy was oxidized at 1000°C for 1 h, the coating surface was covered with a continuous dense Cr₂O₃ layer, and the intermediate layer was mainly composed of W, Si, WO₃ and SiO₂ without Cr elements. The formation of oxide film effectively inhibits the oxidation of WSi₁₂Cr₇ alloy.

Therefore, the service life of the ternary alloy is longer than that of the binary alloy under high temperature and oxygen conditions. In addition, Cr content and oxide layer thickness have an important effect on the oxidation resistance of W-Si-Cr alloys. The surface of WSi₁₀Cr₁₀ alloy with a thickness of 2.5 μm showed bursting after oxidation at 800 °C for 4 h. However, the WSi₁₀Cr₁₀ alloy with a thickness of 4.5 μm maintained an intact surface structure after oxidation at 1000 °C for 22 h. The relatively high Cr content made it easier to form a dense Cr₂O₃ protective film on the surface during the oxidation process, and its oxidation rate was significantly lower than that of W and WSi₁₈.

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.

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