Electrochemical Corrosion Behaviour of Nanocrystalline Materials

Abstract

Nanocrystalline materials have received much attention as a result of their unique physical, chemical and mechanical properties, and have been the subjects of intensive research activities both in the scientific and industrial communities.Nanocrystalline materials -that is, single or multiphase polycrystalline solids with a characteristic grain size of a few nanometers -represent a promising class of new materials. Owing to the extremely small crystallite dimensions (typically 1 to 100 nm), they are characterized structurally by a large volume fraction of interfaces which may lead to improvements in a variety of properties [1].Current spending on corrosion-related problems accounts for more than 3% of the worlds gross domestic product (GDP), and characterization of the corrosion behavior of nanocrystalline materials is important both for prospective engineering applications and for a better understanding of the above fundamental physicochemical properties [2,3]. In many cases the industrial application of novel materials will ultimately depend on their corrosion resistance over extended periods of service. For this reason, corrosion problems must be considered at an appropriate stage of material development.A limited number of investigations have concentrated on the corrosion of nanocrystalline materials. Rofagha et al. [4,5] studied nanocrystalline Ni and Ni-P produced by an electrodeposition technique, whereupon the observed behaviour was considered to be consistent with substantial contributions to the bulk electrochemical behavior from the intercrystalline regions (i.e., grain boundaries and triple junctions) of these materials.Inturi and Szklarska-Smialowska [6] have observed improved localized corrosion resistance in HCl for sputter-deposited nanocrystalline type 304 stainless steel in comparison with conventional material, and attributed this to the fine grain size and homogeneity of the nanocrystalline materials. Thorpe et al. [7] studied the corrosion behavior of nanocrystalline Fe 32 Ni 36 Cr 14 P 12 B 6 alloy obtained by crystallization of the melt-spun amorphous ribbon. These authors determined that the corrosion resistance of this material was significantly greater than that of its amorphous counterpart, and attributed the improvement to the observed greater Cr enrichment of the electrochemical surface via rapid interphase boundary diffusion [8].It is difficult to predict the electrochemical behavior of nanocrystalline materials from the known properties of their coarse-grained polycrystalline analogues. Thus, several groups have observed that nanocrystalline materials exhibit enhanced oxidation and corrosion resistance compared to their conventional microcrystalline counterparts [9][10][11][12]. In contrast, results obtained in other studies have shown nanocrystalline materials to have higher rates of dissolution and corrosion [13,14].The aim of this chapter is to outline the aqueous corrosion research activities currently being undertaken on nanocrystalline materials, with key results being extrac...