目的 在海洋环境中,钛合金构件组装或与异种金属连接时形成的缝隙,极易成为腐蚀介质的渗透通道,由此引发的缝隙腐蚀严重威胁着海洋工程的安全运行。为深入探究这一问题,本研究以TC4钛合金（Ti-6Al-4V）为研究对象,利用自制缝隙腐蚀装置,系统考察了缝隙宽度及缝隙深度对其在含F-溶液中腐蚀行为的影响。方法 采用失重试验、局部电化学等实验方法,结合扫描电子显微镜（SEM）、X射线衍射（XRD）及X射线光电子能谱（XPS）等表征手段,重点分析了腐蚀速率、区域腐蚀产物组成、局部腐蚀电位分布及电化学过程特征。结果 在含F-溶液中,TC4钛合金缝隙内的腐蚀产物主要为TiF3、Na2TiF6和TiO2,且随缝隙深度的增加,TiO2含量逐渐减少,而TiF3与Na2TiF6的含量则呈上升趋势。在0.1~0.3 mm的缝隙宽度范围内,0.2 mm时的缝隙腐蚀最为严重。此宽度下缝隙深处与缝隙口产生的电位差最大,且随腐蚀时间的延长,电位差进一步增大。氧匮乏状态下的“阳极”特征导致缝隙深处的腐蚀加剧并形成半闭塞电池,阳极区Tin⁺累积并水解使pH下降,F-离子迁入,缝隙深处至缝隙口部形成电流回路,使得点蚀坑在缝隙深处优先萌生并长大。结论 在F-离子溶液中,TC4钛合金缝隙腐蚀在缝隙底部最明显,且缝隙底部生成点蚀坑。
Abstract
TC4 titanium alloy holds an indispensable position in numerous fields such as aerospace, marine engineering, chemical processing, and medical applications due to its exceptional specific strength, outstanding corrosion resistance, and excellent biocompatibility. Existing researches indicate that the superior corrosion resistance of titanium alloys primarily stems from the stable, dense passivation film that spontaneously forms on its surface. This passivation film effectively isolates the corrosive medium from direct contact with the metal substrate. However, when titanium alloys serve as connecting components, such as bolts, pipe joints, and welds, crevice corrosion inevitably occurs at these interfaces. Researches indicate that in halide-containing solutions, particularly those with chloride ions (Cl-), crevice corrosion has become one of the most destructive forms of corrosion for titanium and its alloys. Fluoride ions (F-), also belonging to the halogen group, readily adsorb onto the passivation film of TC4 titanium alloy due to their small atomic radius. This poses a serious threat to the stability of the passivation film. Furthermore, F- sources are widespread, such as industrial wastewater discharges and the dissolution of seabed fluorite deposits, among others, generates F- in the environment. Consequently, the detrimental effects of F- on TC4 titanium alloy are difficult to avoid. Most existing studies have been conducted under oxygen-rich conditions. However, in actual service environments, particularly oxygen-depleted zones such as crevices, the corrosion process often becomes significantly more complex. When titanium alloy components are assembled or connected with other dissimilar metals, crevices form. These crevices provide channels for corrosive media in the marine environment, leading to crevice corrosion. This seriously threatens the safe operation of marine engineering. In this work, TC4 titanium alloy (Ti-6Al-4V) was employed to investigate the effect of crevice width and crevice depth on its corrosion behavior with a self-made crevice corrosion device. A combination of weight loss tests, local electrochemical measurements, and characterization techniques (including SEM, XRD and XPS) was used to investigate the corrosion rate, corrosion product composition and electrochemical characteristics. The results indicated that the corrosion products inside the crevice of TC4 titanium alloy were mainly TiF3, Na2TiF6 in the F--containing solution. With the increasing crevice depth, the content of TiO2 gradually decreased while the contents of TiF3 and Na2TiF6 increased. Within a crevice width range of 0.1 to 0.3 mm, the crevice corrosion was the most severe at 0.2 mm. At this specific width, the potential difference between the innermost region of the crevice and its opening reached a maximum and continued to increase with prolonged exposure time. The anodic behavior under oxygen-deficient conditions accelerated corrosion within the inner region, facilitating the formation of a semi-occluded cell. The accumulation and hydrolysis of Tin+ ions in the anodic region lowered the local pH, thereby promoting the inward migration of F- ions. A sustained corrosion current was established in this process, flowing from the inner region to the crevice opening, which resulted in the preferential initiate and growth of pits in the inner region of crevice. In the F--containing solution, the crevice corrosion of TC4 titanium alloy is most pronounced at the bottom of the crevice, with corrosion pits generated there.
关键词
TC4钛合金 /
F-离子 /
缝隙腐蚀 /
缝隙宽度 /
缝隙深度 /
局部电化学测试
Key words
TC4 titanium alloy /
F- ions /
crevice corrosion /
crevice width /
crevice depth /
localized electrochemical testing
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基金
高校院所科技人员服务企业项目（25GXKJRC00035）
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