材料期刊网

摘 要采用模拟“I 8—8不锈钢/c卜”体系腐蚀裂缝形成过程不同阶段的闭塞区溶液.以电化学方法研究了1.8—8不锈钢加载到屈服后在这些溶液中的腐蚀行为。结粜表明:当溶液pH值低于一临界值(约】.8)后受力试样的腐蚀开始加速.而不受力试样加速腐蚀的临界pH值则较低.约为1.5。低于临界值,受力与未受力试样的商蚀电位都从约一200mY.SCE(位于钝化区)突然下降到一400mY左右(处于活化区).表明钝化膜完全破裂。受力屈服后合金的钝化能力变差。将上述闭塞区溶液中测得的动电位极化曲线上的特征电位.电位一时间曲线上所得到的稳定开路电位.放氢平衡线和免蚀线.以及闭塞区腐蚀和放氢动力学曲线等叠加绘制而成的实验电位一pH图,能解释应力腐蚀裂缝内的热力学和动力学行为。

For the 18-8 stainless steel/Cl~- system,polarization scans and linear polarization tests were performed with specimens stressed above yield point and stress free in simulated occluded solutions of different pH and Cl~- concentration representing the chemical condi- tions of different stages in occluded corrosion cell.The results showed that the corrosion of stressed specimens started to accelerate below a critical pH value of about 1.8 at 90℃. while the stress free specimens had a critical pH value about 1.5.The passivating effect al- so decreased for stressed alloy.The open-circuit potentials of both stressed and sterss free specimens dropped suddenly from about-200mV(SCE) in passive region to-400mV (SCE) in active region when pH decreased below the critical value,indicating that the pas- sive film had been ruptured completely.The potential/pH diagrams were constructed by superimposing the above potentiodynamic polarization curves,potential/time curves,and the hydrogen equilibrium curves and immunity border lines which were determined experi- mentally in simulated OC solutions.The potential/pH diagrams interpreted the thermody- namic as well as kinetic behaviour inside stressed cracks.