热处理工艺对Ti-5Ta-5V-8Cr-Al合金耐沸腾硝酸腐蚀性能的影响

Effect of heat treatment process on nitric acid corrosion resistance of Ti-5Ta-5V-8Cr-Al alloy

摘要:

后处理工业所涉及的关键设备如溶解器、蒸发器等长期处于高浓度、高放射性的沸腾硝酸中,保证设备安全可靠运行是首要目标。本文采用全浸腐蚀和电化学腐蚀实验手段研究了热处理工艺对Ti-5Ta-5V-8Cr-Al合金(Ti5581)在6 mol/L沸腾硝酸溶液中的腐蚀行为的影响。结果表明,仅固溶和460 ℃时效时Ti5581合金具有较低的腐蚀速率,腐蚀240 h后腐蚀速率为0.022 mm/a。进一步采用金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、等分析方法分析了Ti5581合金腐蚀后表面钝化膜的结构和成分,表明腐蚀后表层钝化膜平滑且致密,表层钝化膜为Ti和Ta的混合氧化物。研究发现Ti5581合金表层钝化膜的形成与α相的数量和形态相关：与550 ℃高温时效相比,460 ℃低温时效时α相尺寸较小且Ta元素质量分数较高,腐蚀均匀性更好,易于形成致密钝化膜且钝化膜更稳定。

Abstract:

The key equipment in the reprocessing industry, such as dissolvers and evaporators, have continually serviced in boiling nitric acid with high concentration and high radioactivity. Ensuring the safe and reliable operation of the equipment is the primary goal. This article investigated the effect of heat treatment process on the corrosion behavior of Ti-5Ta-5V-8Cr-1Al alloy (Ti5581) in 6mol/L boiling nitric acid solution using full immersion corrosion and electrochemical corrosion experimental methods. The results indicated that Ti5581 alloy has a lower corrosion rate under solid solution only process and 460 ℃ aging process, the corrosion rate was 0.022mm/a after 240 hours corrosion. Further analysis was conducted using metallographic microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and other analytical methods to analyze the structure and composition of the passivation film in the surface layer of Ti5581 alloy after corrosion. After corrosion, the surface passivation film was smooth and dense, and the surface passivation film was composed of a mixed oxide of Ti and Ta. Formation of passivation film in the surface layer of Ti5581 alloy was related to quantity and morphology of α phases. Compared to 550 ℃ aging process, the size of α phase was smaller and the mass fraction of Ta was higher in 460 ℃ aging process, which resulting in better corrosion uniformity and passivation film stability.