Corrosion behavior of Fe-based ferromagnetic (Fe, Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes

Fe-based ferromagnetic [(Fe1−xNix)0.75B0.2Si0.05]96Nb4 (x = 0, 0.2 and 0.4) bulk glassy alloys (BGAs) with a diameter of 2 mm were prepared by copper mold casting. The corrosion behavior of glassy alloy rods obtained was investigated in 0.5 M NaCl, 0.5 M NaOH and 0.5 M H2SO4 aqueous electrolytes, respectively, using weight loss and electrochemical polarization measurements. It was found that the corrosion rates significantly decrease with an increase in Ni content in all examined solutions. The Ni-containing BGAs are spontaneously passivated with wide passive regions and low passive current densities in NaCl and NaOH solutions, but exhibit the active–passive–transpassive behavior in H2SO4 solution. The partial substitution of Ni for Fe results in a considerable improvement on the corrosion resistance of [(Fe1−xNix)0.75B0.2Si0.05]96Nb4 BGAs, because of the structural and chemical homogeneousness of the amorphous phase and the effect of Ni on promoting the formation of a passive film. Besides their high glass-forming ability (GFA), excellent soft-magnetic properties and good mechanical performance, which have been reported before, these FeNi-based BGAs also feature rather high corrosion resistance.