Oxide formation and anodic polarization behavior of thin films of amorphous and crystalline Fe-Cr-P alloys prepared by ion beam mixing

An experimental program has been conducted to determine the effect of phosphorus on the corrosion and passivation behavior of Fe-Cr-P alloys. Chemically homogeneous 60 nm films of Fe-lOCr-xP (x from 0 to 35 at.%) were prepared by multilayer evaporation followed by ion beam mixing with Kr + ions. Films with a phosphorus content of at least 25 at.!% were found to be entirely amorphous, while films with 15 at.% P consisted of both ~o~hous and bee phases. Rec~stallization of the amorphous phase was accomplished by heating the samples to 450°C in a purified argon flow furnace. Electrochemical polarization tests in an acid solution have shown the Fe-IOCr-xP films to be more corrosion resistant than Fe-lOCr, with the corrosion resistance increasing with the amount of P present. The corrosion resistance is not significantly affected when the amorphous films are recrystallized, indicating that the behavior is chemically controlled and not a result of the amorphous structure. When examined by XPS, the phosphorus appears to enhance passivation by encouraging Cr enrichment in the oxide and by incorporating in the oxide as phosphate.