Research progress on high-temperature oxidation resistance of vanadium alloys

Vanadium alloys are an attractive candidate material for advanced fusion reactors’ structural components. Some leading vanadium alloys, such as V−(4−5)Cr−(4−5)Ti alloy, exhibit several important advantages, including excellent strength at elevated temperatures, high resistance to neutron irradiation damage, inherently low long-term activation, as well as good fabricability and weldability. However, the corrosion and embrittlement via oxygen pickup during the high-temperature oxidation process of vanadium alloys remains a key issue, restricting their operation conditions and long service life. In a high-pressure oxygen environment, the main oxidation product V₂O_5, with a low melting point of ～680 ℃, is formed on the vanadium alloy surface, which cannot offer reliable protection to mitigate further oxidation over 650 ℃. However, despite being exposed to a very low-pressure oxygen environment, it is still unlikely for vanadium alloys to form an effective oxidation film to retard the oxygen absorption at temperatures over 450 ℃, mainly due to the high solubility of oxygen in vanadium. When the oxygen concentration reaches 0.2% in the matrix of V−4Cr−4Ti alloy, it can cause severe oxygen embrittlement, possibly due to oxygen accumulation and formation of fine oxidation precipitates at the grain boundaries and the adjacent matrix. Therefore, it is significantly important to enhance the high-temperature oxidation-resistant performance of the vanadium alloy to broaden the operation conditions. In this work, this research progress on the high-temperature oxidation resistance of vanadium alloys is systematically reviewed. In summary, three main methods for enhancing the oxidation–corrosion resistance of vanadium alloys at elevated temperatures are elaborated, i.e., oxidation-resistant element addition, diffusion coating, and overlay coating. Additionally, the characteristics and existing problems of these methods and the responding examples are also analyzed and discussed in detail. In the first two methods, it is impossible to completely isolate the alloy substrate from the service environment; thus, the typical oxidation product V₂O₅ is easily formed in the high-pressure oxygen environment, leading to severe oxidation corrosion and embrittlement, especially at elevated temperatures. Expectedly, the dense overlay coating presents a greater potential application mainly because of the thorough protection from the service environment. Finally, the development trend in the modification and technical requirements of the advanced overlay coatings on high-performance oxidation resistance are prospected in this paper as per the practical application demands for vanadium alloys, aiming to provide a beneficial reference for further research.