新型1200 MPa级Ti-35421合金应力腐蚀敏感性的原位电化学研究

以新型1200 MPa级Ti-35421合金(Ti-3Al-5Mo-4Cr-2Zr-1Fe)为研究对象，采用慢应变速率拉伸实验结合原位电化学监测研究了不同应变速率和阴极保护电位对其应力腐蚀开裂行为的影响。结果表明：当应变速率为1.67×10^-5mm·s^-1时Ti-35421合金在3.5%NaCl溶液中应力腐蚀敏感性最高，其塑性损失和应力腐蚀指数分别为27.27%和0.273；裂纹尖端钝化膜层在应力和腐蚀的共同作用下钝化保护弱于溶解，导致了应力腐蚀加剧；当外加阴极保护电位为-600mV时Ti-35421合金在3.5%NaCl溶液中的应力腐蚀敏感性最低，其最佳阴极保护电位范围为-450～-600 mV，降低了阳极共轭反应，从而使其塑性损失和应力腐蚀指数分别降低到1.01%和0.113。

In-situ electrochemical study on susceptibility to stress corrosion cracking of new-developed 1200 MPa Ti-35421 titanium alloy

The effects of different strain rates and cathodic protection potential on the stress corrosion cracking (SCC) behavior of new-developed 1200 MPa Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe) alloy have been investigated by using slow strain rate test combined with in-situ electrochemical monitoring. The results indicate that Ti-35421 alloy has the highest SCC susceptibility in 3.5% NaCl solution at the strain rate of 1.67×10-5 mm s-1. The plastic loss and stress corrosion index of Ti-35421 alloy are confirmed to be 27.27% and 0.273, respectively. The passivating ability of the passivation films in the crack tips is considered to be weaker than active dissolution under the combined interaction of applied stress and corrosive media especially with strain rate of 1.67×10-5 mm s-1, which results in the intensification of SCC. When the cathodic protection potential is set at -600 mV, the SCC susceptibility of Ti-35421 alloy in 3.5% NaCl solution is the lowest. The range of the optimal cathodic protection potential is measured to be from -450 to -600 mV. The reduction of the plastic loss and stress corrosion index of Ti-35421 alloy down to 1.01% and 0.113 is ascribed to the slower conjugated anodic reaction kinetics under the cathodic protection.