Corrosion behavior of CoCr films in Sulfuric acid

The corrosion behavior of CoCr films (∼500 to 1000 nm thick) deposited on glass by RF sputtering has been examined by classical electrochemical methods which provide a simple and rapid means for comparing one material with another. The development of a specially designed holder to allow electrical contact to the film and exposure to a sulfuric acid electrolyte was required. A comparison of potentiodynamic polarization curves for films containing various amounts of Cr with similar data from the literature for bulk CoCr alloys showed analogous behavior in the shape of the curve and in the level of Cr required to produce passivity, about 15-17%. Results indicate the formation of a passive layer containing a chromium oxide. In addition, comparison of an as-received sample with an electrochemically treated sample using Auger electron spectroscopy along with polarization results showed that Co oxides are apparently stabilized by the presence of Cr. Auger results also suggest that corrosion and passivation occur along the spaces or crevices between columnar grains during electrochemical treatment as indicated by the presence of a significant oxygen content.