基于扫描电化学显微镜研究316L不锈钢的局部腐蚀行为

Local Corrosion Behavior of 316L Stainless Steel Studied by Scanning Electrochemical Microscope

通过电化学试验获得316L不锈钢在NaCl溶液中的动电位极化曲线,确定了特征电位;采用扫描电化学显微镜研究了不锈钢在NaCl溶液中不同特征电位下的局部腐蚀行为。结果表明:在开路电位(-0.1 V)下极化后,面扫描图像中未见明显的电化学活性点,基底背景电流变化较小,钝化膜具有较好的稳定性;在自腐蚀电位(-51.2 mV)下极化后,面扫描图像中存在一个电化学活性点,但峰值电流降低,基底背景电流稳中有降,不锈钢发生自钝化;在典型钝化电位(100 mV)下极化后,表面发生亚稳态点蚀的不断萌生与钝化,基底背景电流先降低后保持稳定,表面自钝化程度更高;在点蚀电位(568 mV)下极化后,表面出现稳态点蚀坑,极化停止后点蚀坑被钝化,基底背景电流较极化前下降,表明未发生点蚀处钝化膜的稳定性增强。

The potentiodynamic polarization curve of 316L stainless steel in NaCl solution was obtained by electrochemical test,and the characteristic potential was determined.The local corrosion behavior of stainless steel at different characteristic potentials in NaCl solution was studied by scanning electrochemical microscope.The results show that after polarization at the open circuit potential(-0.1 V),no obvious electrochemical active point was found in the surface scan image,and the substrate background current changed little,indicating good stability of the passivation film.After polarization at the self corrosion potential(-51.2 mV),there was an electrochemical active point in the surface scan image,but the peak current decreased and the substrate background current was stable with a slight decrease,indicating the existence of self passivation behavior in stainless steel.After polarization at a typical passivation potential(100 mV),the surface underwent continuous initiation and passivation of metastable pitting;the background current of the substrate first decreased and then remained stable;the degree of surface self passivation was higher.After polarization at the pitting potential(568 mV),steady-state pitting pits appeared on the surface,and after polarization stopped,the pits were passivated;the substrate background current decreased compared to that before polarization,indicating an enhanced stability of the passivation film in the non-pit areas.