Electrodeposited free-crack NiW films under super gravity filed: Structure and excellent corrosion property

The anti-corrosion ability of electrodeposited metal films depends on surface structure of films. In this paper, NiW films with or without cracks were electrodeposited by using super gravity field. The structure and corrosion behavior (corrosion resistance and long-term stability) of NiW films were characterized and studies by SEM, XRD, EDS, Tafel and electrochemical impedance spectroscopy (EIS). The dependence and mechanism of corrosion behavior on film structure were discussed. NiW film with long cracks electrodeposited under normal gravity condition (G = 1) consist of hundreds of micron fragments. For NiW films electrodeposited under super gravity field, fragments of NiW films were refined to about 10-30 μm or cracks were eliminated. The anti-corrosion ability for free-crack NiW films was better than that for NiW film with cracks. Meanwhile, corrosion resistances of NiW films without cracks increased with exposure time in NaCl solution. However, the corrosion resistances of NiW film with cracks only increased in the first 24 h, then decreased with exposure time. After 144 h exposure in NaCl solution, corrosion resistance is up to 12.54 kΩ cm2 for free-crack NiW film. The value is much higher than that (1.56 kΩ cm2) for NiW film with cracks. Lots of corrosion pits were only formed on the surface of NiW film with cracks. The excellent anti-corrosion properties of free-crack NiW films are ascribed to homogeneous and compact surface (i.e. free-crack surface and fine grain).