摘要
采用楔形张开加载(WOL)试样开展应力腐蚀试验,研究TC4钛合金在 3.5%NaCl溶液中的应力腐蚀行为,分析应力腐蚀开裂(SCC)机理.结果表明,腐蚀24h后,即可在试样表面观察到SCC裂纹.腐蚀30d和75d的试样,SCC裂纹长度接近,且都明显大于腐蚀15d的试样,说明 15～30 d内SCC扩展终止.试样的加载应力越大,裂纹长度越长,随着裂纹扩展,应力逐渐松弛,当残余KI值降低到38 MPa·m1/2附近时,SCC扩展终止.SCC扩展是应力和腐蚀耦合作用的过程,在SCC起始阶段,应力主导裂纹快速扩展,断口呈韧窝形貌.SCC中后阶段,断口呈解理形貌和鳞片状花样,鳞片边缘存在钛氧化物,推测是由于应力松弛后的裂纹间歇性驻留和阳极溶解促进的裂纹继续扩展反复交替作用形成的.
Abstract
A stress corrosion cracking(SCC)test of TC4 titanium alloy in 3.5%NaCl solution was carried out,using wedge opening loading(WOL)specimens.The SCC behavior and mechanism were analyzed.The results show that the SCC propagation can be identified on the surface of specimen after 24 hours.The SCC lengths of specimens corroded for 30 days are similar with that of the specimens corroded for 75 days.And both are significantly longer than that of the specimens corroded for 15 days.This indicates that SCC propagation terminated within 15-30 days.The SCC crack length increases with the enhancement of loading stress.Stress relaxation occurs along with crack extending,resulting in continuous reduction of residual KI.When residual KI value decreases to about 38 MPa·m1/2,SCC propagation terminates.SCC behavior of the specimen could be attributed to coupling effect of stress and corrosion.Stress dominates the fast crack propagation at the initial stage of SCC,and the fracture surface presents dimple morphology.While the fracture surface exhibits cleavage morphology with scaly pattern at middle and later stages of SCC.And titanium oxide is found at the edge of scaly pattern.That is supposed to result from alternate repetition of crack residency after stress relaxation and crack continuous propagation assisted by anodic dissolution
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