Surface analyses of anodic oxides films formed on Fe-3% Ti alloy

Abstract

Surface analyses of the anodic oxide films formed on Fe—3% Ti alloy in deaerated pH 3.0 phosphate solution were performed with Auger electron spectroscopy (AES) and ellipsometry to evaluate the role of allying titanium in the corrosion resistance of iron. The 3%-addition of titanium reduced significantly the passivity-maintaining current density of iron as well as the maximum-active current density. Auger analysis revealed that titanium was enriched markedly in the anodic oxide films formed on Fe—3% Ti alloy and that a significant amount of phosphorus was distributed in the whole range of film thickness. Both the amount of titanium enriched in the film and the film thickness (20–40 nm) ellipsometrically obtained were proportional to the amount of electric charge required for passivation. Atomic absorption analysis of the solution indicated that the formation of a titanium-enriched film resulted from a preferential dissolution of iron as ferrous ions. From the measurement of the potential decay curves of the Fe—3% Ti alloy and pure iron electrodes passivated for different hours, it was concluded that the titanium-enriched layer promoted the passivity by suppressing, though incompletely, the active dissolution, whereas the substantial passivity of the alloy was attributed to the iron oxide film of barrier type formed at the interface of titanium-enriched layer/alloy substrate.