外加压应力对Ti-35421合金钝化膜损伤修复影响的原位电化学研究

Effects of Compressive Stresses on the Breakdown and Self-Healing of the Surface Passivation Films on Ti-35421 Alloy by In-situ Electrochemical Monitoring

以Ti-35421(Ti-3Al-5Mo-4Cr-2Zr-1Fe)合金为研究对象,采用自制的钝化膜损伤修复原位电化学测试装置研究了模拟深海静水压力对Ti-35421合金经过Al_(2)O_(3)陶瓷刀划伤后钝化膜破裂损伤和自修复的原位电化学行为。Ti-35421合金在3.5%NaCl溶液中的钝化平台为-0.27~0.01 V。在-0.13 V钝化电压条件下极化并进行划痕实验,无压应力作用时破损钝化膜发生快速修复。压应力增大导致原子间结合力降低,金属溶解速度增加,再钝化减缓,在原位电化学上表现为电流上升,电流回复时间增长,自修复能力减弱。再钝化过程中的暂态阶段钝化膜生长符合线性高场模型。观察划痕形貌发现压应力下划痕槽中出现微裂纹,说明较高压应力损伤作用下在划痕槽近表面产生应力集中,对合金产生的伤害部分不可修复。钝化膜破损加剧和自修复能力减弱是残余应力与环境腐蚀共同作用的结果。

The effects of compressive stresses on the breakdown and self-healing of the surface passivation films on Ti-35421(Ti-3Al-5Mo-4Cr-2Zr-1Fe)alloy after damaging by the Al2O3 ceramic needles have been investigated on a self-made scratching tester by using the in-situ electrochemical monitoring.The passivation potential of Ti-35421 alloy in 3.5%NaCl solution is determined to be-0.27~0.01 V.Without the compressive stress,the potential recovers to the initial level shortly.When the scratching experiments carry out under the passivation polarization of-0.13 V,the increase of compressive stress leads to the decrease of the atomic binding forces,the increase of metallic dissolution rates,and the slow down of repassivation rates.In-situ electrochemical data shows that the currents rise and the self-healing duration time becomes longer.The growth and sel-healing of the passive films in the transient stage basically conform to the linear high-field model.The scratched morphology shows that the scratching generates the higher residual stresses at the bottom of the grooves.It is found that microcracks appear in the scratch grooves under the compressive stresses basing on the scratch morphology,indicating that the damages of the scratches under high compressive stresses are partialy unrecoverable,which results from the synergetic effects of the residual stresses and environmental corrosion.