Effect of nanosized NiAl precipitates on the corrosion resistance of the superelastic Fe–Mn–Al–Ni–Nb–C alloy

Abstract

Nanosized NiAl precipitates, which are generally regulated by aging treatment, are regarded as an ordered phase for the enhancement of superelasticity for Fe–Mn–Al–Ni alloys. However, the role of such intermetallic compounds in the corrosion resistance of Fe–Mn–Al–Ni alloys is poorly understood. Herein, we demonstrated the deleterious effect of nanosized NiAl precipitates on the corrosion resistance of Fe–Mn–Al–Ni system alloys by a comparative study of Fe–Mn–Al–Ni–Nb–C (NC) alloy with solid solution-treatment (NC-S) and the NC-S with an additional aging treatment (NC-SA). The NC-SA with dispersed NiAl precipitate showed a weaker corrosion resistance in 3.5 wt% NaCl solution compared to the NC-S. This is ascribed to the fact that the surface potential of the nanoscale NiAl precipitates (∼46 ± 5 nm) is about 23 mV lower than the adjacent matrix, thus preferentially corroding and forming microcavities. Accordingly, the microcavities expanded upon encountering shallow pits produced by the shedding of NbC precipitate, hastening the exfoliation of the passive film and diminishing NC-SA's corrosion resistance. Our findings reveal the role of ordered NiAl precipitate and provide insights into the design of the Fe–Mn–Al–Ni alloys with improved superelasticity and corrosion resistance.