Grain size effects on the corrosion behavior of Ni50.5Ti49.5 and Ni45.6Ti49.3Al5.1 films

In this paper, the various grain sizes of Ni50.5Ti49.5 and Ni45.6Ti49.3Al5.1 film were prepared by various annealing temperatures. The electrochemical corrosion behavior of smaller grain size Ni50.5Ti49.5 and Ni45.6Ti49.3Al5.1 films compared with coarse-grained coatings in chloride-containing corrosion media were characterized using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results showed that in the chloride-containing electrolyte, the smaller grain size Ni50.5Ti49.5 and Ni45.6Ti49.3Al5.1 exhibited improved corrosion resistance when compared with coarse grain films, which is attributed to the higher grain boundary density in fine structure to quickly form a noble and protective passive film. The enhancement of corrosion resistance can be related to the positive effect of the high fraction density of grain boundary in fine structure materials.