Nanocrystalline metal Cr is prepared by mechanical alloying through hot-pressing processes and its corrosion mechanism and corrosion resistances in media containing chloride ions is also investigated as compared with corresponding coarse-grained alloy. Results show that with the increment of chloride ion concentrations

the corrosion current densities increase and therefore corrosion rates become faster. After the grain size is refined

the corrosion current densities of nanocrystalline Cr are bigger than those of the corresponding coarse grained materials. This indicates that the corrosion resistances decrease when the grain size is refined. Two kinds of grain size metal Cr produce passivating phenomena

but they become weaker initially and afterwards stronger alternately with the increment of chloride ion concentrations. These results indicate that chloride ions act on destroying and restoration. The electrochemical impedance spectroscopy (EIS) of the two alloys in media containing chloride ions is composed of single capacitive loop

therefore corrosion process is controlled by electrochemical reaction.