Passivation ability of nanocrystalline materials

2 Potentiodynamic polarization plots of the conventional coarse crystalline Ni-based alloy and the corresponding NC coating in 3.5% NaCI solution.22 

In order to understand the effect of nanocrystallization in detail, the passive film on an Ni-based alloy has been studied. X-ray photoelectron spectroscopy (XPS) results indicated that the composition of the passive film was significantly different between the NC coating and the corresponding traditional coarse ciystalline alloy. The passive film on the conventional alloy consisted of Cr, Ti and Ni oxides, whereas only Cr and Ti oxides were present in the passive film on the NC coating. There were distinctly different qnantities of the elements present in the two passive films. As shown in Table 4.more Cr exists in the passive film on the NC coating. The resnlts testified that nanociystallization improved the enrichment of passive elements in the passive film, which may be one of the main reasons for the high corrosion resistance of nanomaterials. 

From these results it can be inferred that, during passivation, Ti and Cr oxides were formed first The passive film could not form a continuous layer rapidly because of the large grain size of the coarse ciystalhne alloy. Therefore, elemental 

Regarding the adsorption of Cl on the surface of materials, Intrui and Szklarska-Smialowska theorized that the presence of a large number of defects would result in a high degree of distribution of Cl on the metal surface. The Cl concentration at each of the defects of fine-grained NC materials is greatly reduced when compared with the case of coarse-grained materials. As a result, localized enrichment of Cl and subsequent acidification at 

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