Nanocrystallization effect on the surface electron work function of copper and its corrosion behaviour

The effect of grain size at micro- and nanoscale on the surface electron stability of copper as reflected by the electron work function (EWF) was investigated. In the ambient environment, the surface reactivity increases with decreasing grain size in the micron range, but decreases when entering the nanometre range. When in a solution with associated passivation, grain refinement enhances resistance to corrosion. However, the situation is reversed when no passivation is involved. In the former case, the improved surface stability and corrosion behaviour caused by nanocrystallization can be attributed to the formation of a more protective passive film. In the latter case, nanocrystallization accelerates material dissolution resulting from enhanced activity of surface electrons at high-density grain boundaries. The correlation between EWF and the corrosion behaviour, as well as the mechanisms involved, are discussed.