ELECTROCHEMICAL ATOMIC FORCE MICROSCOPIC STUDIES ON THE LOCALIZED CORROSION IN SPUTTERED CHROMIUM NITRIDE THIN FILM

摘要

Electrochemical atomic force microscopy (ECAFM) has become a useful tool to study the surface properties and reactions of corrosion down to atomic scale. With the aid of electrochemical control, detailed surface morphology changes can be in-situ observed. In this study, the 3.5 wt% sodium chloride aqueous solution was employed to be the corrosive media to investigate the corrosion behavior of a sputtered chromium nitride thin film on Fe-Mn-Al alloy substrate. Insitu time-lapse sequences of images were obtained using the ECAFM. Localized pittings were observed on the thin film surface. The surface roughness increased due to the corrosion reaction. Some corrosion products were observed around and inside the corrosion pit. As long as the CrN film was penetrated by the corrosive electrolyte, the galvanic corrosion of the exposed Fe- Mn-Al alloy substrate dominated the corrosion reaction. An attacked large pit on the CrN thin film and the exposed substrate was found. The eruption of the hydrogen gas along the CrN film and Fe-Mn-Al alloy substrate interface made the cracking and spallation of CrN thin film.