Effect of Crystal Orientation on the Initial Stage of Pore Formation in Ant Nest Corrosion

To investigate the starting points and progression directions of ant nest corrosion, semi-immersion test was conducted using oxygen-free copper. A formic acid solution was used as the test solution. The results revealed that the starting point of pores was primarily formed at grain boundary triple junctions. Furthermore, EBSD was used to measure the crystallographic misorientation in the areas around the pits induced by ant nest corrosion. The average of crystallographic misorientation at grain boundary triple junctions was most frequently observed at 53°, followed by a peak at 45°. On the other hand, ant nest corrosion occurred most frequently at approximately 33°, which is considered to have the highest grain boundary energy. Therefore, it was clarified that the starting point of ant nest corrosion is grain boundary triple junctions with high grain boundary energy.