热处理工艺对Ti-5Ta-5V-8Cr-1Al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-1Al Alloy

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。本工作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-1Al(Ti5581)合金在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。

The key equipments in the reprocessing industry,such as dissolvers and evaporators,have continually serviced in boiling nitric acid with high concentration and high radioactivity.It is the primary goal to ensure the safe and reliable operation of the equipment.This research investigated the effect of heat treatment process on the corrosion behavior of Ti-5Ta-5V-8Cr-1Al alloy(Ti5581) in 6 mol/L boiling nitric acid solution using full immersion corrosion and electrochemical corrosion experimental methods.The results indicate that Ti5581alloy has a lower corrosion rate under only solid solution process and 460 ℃ aging process,and the corrosion rate is 0.022 mm/a after240 h corrosion.Metallographic microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD) and other analytical methods were used to further analyze the structure and composition of the passivation film in the surface layer of Ti5581 alloy after corrosion.After corrosion,the surface passivation film is smooth and dense,which is composed of a mixed oxide of Ti and Ta.Formation of passivation film in the surface layer of Ti5581 alloy is related to quantity and morphology of αphase.Compared with the case of 550 ℃ aging process,the size of α phase is smaller and the mass fraction of Ta is higher in 460 ℃ aging process resulting in better corrosion uniformity and passivation film stability.