The initial stage of atmospheric corrosion on interstitial free steel investigated by in situ SPM

The initial stage of atmospheric corrosion on interstitial free steel was investigated by ab initio calculation and scanning probe microscopy under different operation modes. Water droplets are adsorbed preferentially on grain boundaries at 95% relative humidity due to their higher surface energy, which is confirmed by ab initio calculation. Atomic force microscopy observation indicates that corrosion preferentially occurs at grain boundaries after immersion under a thin film of NaCl electrolyte, because of the lower relative nobility of grain boundary, which is proved by scanning Kelvin probe force microscope. These results indicate that water adsorption is crucial for initializing atmospheric corrosion.

► The initial stage of atmospheric corrosion on interstitial free steel was studied.
► Water droplets are adsorbed preferentially on the grain boundaries.
► Ab initio calculations prove the grain boundary has higher surface energy.
► AFM image indicates the corrosion preferentially occurs at grain boundary.
► SKPFM image proves the grain boundary has lower relative nobility than the grain.