Oxidation Behavior of W-Cr-Ti Ternary Alloys

Garcia et al. produced W-Cr-Ti ternary alloys—WCr12Ti2.5 (wt%) alloys by MA and hot isostatic pressing (HIP) techniques and investigated the oxidation behavior of the alloy. The results showed that the Δ m/S of the WCr₁₂Ti_2.5 alloy was 1.25 × 10^-2 to 4 × 10^-2 times higher than that of the W-Cr alloy during the first 15 h of oxidation at 800 °C. In addition, the former is 2 × 10^-2 to 5 × 10^-2 times higher than the latter for the first 5 h of oxidation at 1000 °C. With increasing oxidation time, the oxide layer of the WCr₁₂Ti_2.5 alloy becomes thicker and its porosity gradually increases. In addition, the oxidized alloy has a similar cross-sectional structure, consisting of black, dark gray and light gray phases from inside to outside, respectively.

Cross-sectional and EDS mapped images of the alloy after isothermal oxidation show that the black outermost layer is Cr₂O₃ and the dark gray intermediate layer is composed of Ti, W, small amounts of Cr and other oxides. In addition, the bottom of the Cr₂O₃ layer consists of Cr₂WO₆ and Ti₂CrO₅ layers, followed by a mixed region consisting of Ti₂CrO₅ and WO₃. This indicates that the diffusion rate of Ti⁴⁺ and Cr³⁺ cations outward is greater than that of W³⁺ cations.

More importantly, there is a large amount of irregular scale growth in the form of "waves" in the outer region, and its thickness is not uniform. This is due to the large amount of oxides generated and compressive stresses released during the oxidation process, which led to the cracking of the thinner regions of the Cr₂O₃ layer. As a diffusion barrier, the Ti₂CrO₅ layer inhibits the internal diffusion of O^2-, which gives the alloy better oxidation resistance than the W-Cr alloy. For the oxidation behavior, although both the internal oxidation zone and the bulk alloy zone are relatively smooth, there are still some holes in them. This indicates that some oxygen still enters the alloy and oxidizes the W-rich phase.

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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