Due to their high grain boundary density, nanocrystalline materials possess unusual mechanical, physical and chemical properties. Extensive research on nanocrystalline materials has been conducted in recent years. Many studies have shown that corrosion, one of important properties of nanocrystalline materials, is crucial to their applications. In this article, the activity of electrons at grain boundaries of metallic surfaces is analyzed based the electron work function (EWF), the minimum energy required to attract electrons from inside a metal. It is demonstrated that at grain boundaries, the electron work function decreases, indicating that at a grain boundary, electrons are more active. As a result, the surface becomes more electrochemically reactive. Such increase in electrochemical reactivity has negative effect on the corrosion resistance of nanocrystalline materials. However, for a passive nanocrystalline metal or alloy, the nanocrystalline structure is beneficial to its corrosion resistance through rapid formation of a protective passive film. The mechanisms responsible for the variation in EWF at grain boundary and effects of nanocrystallization on corrosion are discussed in this article.

Influence of ultraviolet (UV) light irradiation on the corrosion behavior of electrodeposited Ni and Cu nanocrystalline foils in 3.5% NaCl solution was studied by means of electrochemical methods, electron work function (EWF) analysis, and characterization with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the influence of solar light on corrosion of the metals was non-negligible, which could be very different for different materials. The UV light irradiation resulted in an increase in corrosion resistance of the Cu foil but showed an opposite influence on that of the Ni foil. Based on surface state analysis, it was concluded that the UV irradiation altered the surface oxide films. The UV light induced the formation of Cu2O on Cu, which is more stable and compacted than naturally formed CuO film. However, the UV light accelerated the formation of Ni2O3, which is loose, porous and brittle, compared to naturally formed NiO on Ni. The changes in oxide films were responsible for the opposite variations in the corrosion behavior of the Cu and Ni nanocrystalline foils caused by the UV light irradiation.

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