Extremely High Corrosion Resistance of Chromium-Bearing Amorphous Iron Alloys

Amorphous iron alloys containing 8 at.% or more chromium did not suffer pitting and crevice corrosion, and no detectable weight change was observed after immersion for a week in several neutral and acidic solutions in which ordinary stainless steels unavoidably suffer pitting and crevice corrosion. According to ESCA study, passive film on the amorphous Fe-Cr-P-C alloy consisted mainly of protective chromium oxy-hydroxide and contained some bound water. Electrochemical measurements revealed that more uniform passive film was formed on the amorphous alloy as compared with crystalline alloy having the same composition inasmuch as the amorphous alloy is composed of a homogeneous single phase without crystal defects acting as initiation sites for corrosion. The formation rate of passive film on the amorphous alloy was higher than that on ordinary stainless steels because of high reactivity of amorphous alloy without passive film. Consequently, extremely high corrosion resistance of the amorphous alloys can be interpreted in terms of rapid formation of thick, uniform, highly corrosion resistant passive film