Corrosion behavior and composition analysis of chromate passive film on electroless Ni-P coating

A passive film was formed on electroless Ni-P coating (ENPC) in a bath of K2Cr2O7 30 g/l. XPS and electrochemical methods were employed to analyze its chemical compositions and corrosion behaviors. The potentiodynamic polarization tests indicated the corrosion current of the passivated sample was 1/30 that of as-plated ENPC. The XPS analysis illustrated the film comprised Cr, Ni and O. The film thickness was evaluated to be a few nanometers according to the sputtering rate of Ar+ ion. High-resolution XPS spectra suggested that the detected Cr in film was in the form of trivalent compounds, Cr2O3 and Cr(OH)3.