Aramco Research Center - Boston, Aramco Americas, Cambridge, Massachusetts 02139, United States.
Sandia National Laboratories, Center for Integrated Nanotechnologies, Albuquerque, New Mexico 87185, United States.
Nano Lett. 2022 Sep 14;22(17):7087-7093. doi: 10.1021/acs.nanolett.2c02122. Epub 2022 Sep 1.
Nanoscale, localized corrosion underpins billions of dollars in damage and material costs each year; however, the processes responsible have remained elusive due to the complexity of studying degradative material behavior at nanoscale liquid-solid interfaces. Recent improvements to liquid cell scanning/transmission electron microscopy and associated techniques enable this first look at the nanogalvanic corrosion processes underlying this widespread damage. Nanogalvanic corrosion is observed to initiate at the near-surface ferrite/cementite phase interfaces that typify carbon steel. In minutes, the corrosion front delves deeper into the material, claiming a thin layer of ferrite around all exposed phase boundaries before progressing laterally, converting the ferrite to corrosion product normal to each buried cementite grain. Over the following few minutes, the corrosion product that lines each cementite grain undergoes a volumetric expansion, creating a lateral wedging force that mechanically ejects the cementite grains from their grooves and leaves behind percolation channels into the steel substructure.
纳米级、局部腐蚀每年造成数十亿美元的损失和材料成本；然而，由于研究纳米尺度液-固界面下降解材料行为的复杂性，导致负责的过程仍然难以捉摸。最近对液相扫描/透射电子显微镜及相关技术的改进，使我们能够首次观察到这种广泛破坏的纳米电偶腐蚀过程。观察到纳米电偶腐蚀是从典型碳钢的近表面铁素体/渗碳体相界面开始的。几分钟内，腐蚀前沿就会深入到材料内部，在横向扩展之前，先从所有暴露的相界上夺取一层薄薄的铁素体，将铁素体转化为与每个埋入的渗碳体颗粒垂直的腐蚀产物。在接下来的几分钟内，排列在每个渗碳体颗粒上的腐蚀产物会发生体积膨胀，产生一个侧向楔入力，将渗碳体颗粒从其凹槽中机械地弹出，并在钢的子结构中留下渗透通道。
