海水环境中Ti6321焊接接头点蚀萌生与生长模型

Pitting initiation and growth model of Ti6321 welded joint in seawater environment

针对钛合金焊接接头在海水中长期服役可能面临的点蚀风险,通过电化学测试、预制点蚀凹坑试样的弯曲加载浸泡试验,结合累积概率、分布函数等统计学分析方法研究了Ti6321焊接接头在海水环境中的点蚀萌生和生长行为,利用极值统计法建立了点蚀生长动力学模型。结果表明:点蚀萌生时间包括点蚀萌生的驱动电位达到阈值的时间和亚稳态点蚀产生并向稳态点蚀转变的诱导时间,根据点蚀萌生时间的试验和理论推算结果保守估计,在静态海水自然腐蚀条件下,Ti6321焊接接头难以自发产生稳态点蚀;90%R_(e)弯曲加载条件下Ti6321焊接接头在海水中的最大点蚀深度符合Gumbel分布。本研究为钛合金在海水环境中点蚀萌生和生长提供了一种基于电化学、统计分析的快速试验和预测方法。

In view of the pitting risk that titanium alloy welded joints may face in long-term service in seawater,the pitting initiation and growth behavior of Ti6321 welded joint in seawater environment were investigated by electrochemical testing,bending loading and immersion test of prefabricated pitting specimens,combined with statistical analysis methods such as cumulative probability and distribution function.A kinetic model of pitting growth was established by using extreme statistical method.A kinetic model of pitting growth was establised by using extreme statistical method.The results show that the initiation time includes the time when the driving potential of pitting initiation reaches the threshold potential and the induction time of the generation of metastable pitting and its transition to steady pitting.Based on the experimental and theoretical calculation results of pitting initiation time,it is conservatively estimated that under free corrosion conditions in stagnant seawater,it is diffucult for Ti6321 welded joints to spontaneously produce steady-state pitting corrosion.The maximum pitting depth of Ti6321 welded joint in seawater under 90%R_(e) bending loading conforms to the Gumbel distribution.This study provides a prediction method based on electrochemical and statistical analysis for the quantitative evaluation for pitting initiation and growth of titanium alloy in seawater environment.