NanoSIMS investigation of passive oxide films on high-Cr cast iron

The discrete depth characteristics of thin passive oxide films were investigated using high-resolution electron microprobe and nanoscale secondary ion mass spectrometry (NanoSIMS). A novel NanoSIMS method involving a Cs layer deposition before Cs+ sputtering was employed for the first time to determine the elemental distribution at different sub-layers of a passive film. The film was formed in air on the surface of a multi-phase microstructure of high-chromium cast iron (HCCI). It was found that the film composition and thickness varied according to the underlying microstructure phase. Based on the microprobe and NanoSIMS results, the influence of the HCCI passive film thickness and composition on the localized passivity breakdown has been proposed.