Liu Haochen, Bai Xuehan, Li Zhen, Fan Lin, Tang Junlei, Lin Bing, Wang Yingying, Sun Mingxian
State Key Laboratory for Marine Corrosion and Protection, Luoyang Ship Material Research Institute (LSMRI), Qingdao 266237, China.
College of Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China.
Materials (Basel). 2022 Apr 28;15(9):3201. doi: 10.3390/ma15093201.
Titanium alloys have high specific strength and excellent corrosion resistance and have been applied in deep-sea engineering fields. However, stress corrosion cracking may become one of the biggest threats to the service safety of a high-strength titanium alloy, as well as its weldment. In this work, stress corrosion cracking of a gas-tungsten-arc-welded Ti-6Al-3Nb-2Zr-1Mo (Ti6321) alloy influenced by the applied potentials in simulated deep-sea and shallow-sea environments was investigated by combining slow strain rate testing with electrochemical measurements. The results showed that the service environment and applied potential have a substantial effect on the stress corrosion cracking behavior of the Ti6321 welded joint. The Ti6321 welded joint exhibited higher stress corrosion susceptibility in a simulated deep-sea environment and at a strong polarization level owing to the diminishing protection of the passive film under passivation inhibition and the enhancement of the hydrogen effect. The fracture of a Ti6321 welded joint in the weld material could be attributed to the softening effect of the thick secondary α within the coarse-grained martensite. The electrochemical evaluation model of stress corrosion cracking susceptibility of a Ti6321 welded joint in a simulated marine environment was established by adding the criterion in the passivation region based on the literature model, and four potential regions corresponding to different stress corrosion cracking mechanisms were classified and discussed. Our study provides useful guidance for the deep-sea engineering applications of Ti6321 alloys and a rapid assessment method of stress corrosion risk.
钛合金具有高比强度和优异的耐腐蚀性，已应用于深海工程领域。然而，应力腐蚀开裂可能成为高强度钛合金及其焊件服役安全的最大威胁之一。在这项工作中，通过将慢应变速率试验与电化学测量相结合，研究了在模拟深海和浅海环境中，外加电位对钨极气体保护电弧焊Ti-6Al-3Nb-2Zr-1Mo（Ti6321）合金应力腐蚀开裂的影响。结果表明，服役环境和外加电位对Ti6321焊接接头的应力腐蚀开裂行为有显著影响。由于钝化抑制下钝化膜保护作用的减弱和氢效应的增强，Ti6321焊接接头在模拟深海环境和强极化水平下表现出更高的应力腐蚀敏感性。Ti6321焊接接头焊缝处的断裂可归因于粗晶马氏体中粗大二次α相的软化作用。基于文献模型，通过在钝化区添加判据，建立了Ti6321焊接接头在模拟海洋环境中应力腐蚀开裂敏感性的电化学评价模型，并对对应不同应力腐蚀开裂机制的四个电位区域进行了分类和讨论。我们的研究为Ti6321合金的深海工程应用及应力腐蚀风险的快速评估方法提供了有益的指导。
