钛合金应力腐蚀开裂机理的研究

用微电极法和 pH 试纸法直接测定了 Ti-5 Al-2.5Sn 和 Ti-5 Al-4V 在近中性3.5%wt.NaCl 水溶液中应力腐蚀裂纹顶端溶液的 pH 值,结果在1.7到2.0范围内。模拟实验的结果与上述结果一致。金相跟踪观察证明上述钛合金应力腐蚀裂纹的扩展过程是首先在裂纹前端的塑性区中形成若干小裂纹,然后主裂纹与小裂纹相对扩展并最后连通。用扫描电镜检查了应力腐蚀开裂(SCC)断口形貌。基于这些结果,作者提出并讨论了钛合金 SCC 的模型。

A STUDY OF THE MECHANISM OF SCC OF TITANIUM ALLOYS

The pH value of the crack tip solution of both Ti-5Al-2.5Sn and Ti-5Al- 4V under stress corrosion was measured by micro-electrode methol and indi- cator paper method to be 1.7 to 2.0,while the bulk solution of 3.5%wt NaCl- was nearly neutral.The results so obtained are in good agreement with those obtained from the simulation experiment.The propagation of the SCC was observed dynamically by optical microscope and was proved as follows:some mierocraeks first formed in the plastic region in front of the crack tip, then both the main crack and microcracks extended to each other and con joined finally.The fractography of the SCC was examined by SEM.Based on these experimental results,a model for the SCC of titanium alloys is proposed and discussed.