Role of Cr Element in Highly Dense Passivation of Fe-Based Amorphous Alloy

The effect of the Cr element on the corrosion behavior of as-spun Fe_72-CrB_19.2Si_4.8Nb₄ ribbons with x = 0, 7.2, 21.6, and 36 in 3.5% NaCl solution were investigated in this work. The results show that the glass formability of the alloys can be increased as Cr content (c_Cr) is added up to 21.6 at.%. When c_Cr reaches 36 at.%, some nanocrystals appear in the as-spun ribbon. With increasing c_Cr content, the corrosion resistances of as-spun Fe-based ribbons are continually improved as well as their hardness properties; during the polarization test, their passive film shows an increase first and then a decrease, with the highest pitting potential as c_Cr = 7.2 at.%, which is confirmed by an XPS test. The dense passivation film, composed of Cr₂O₃ and [CrO(OH)_3-2, nH₂O], can reduce the number of corrosion pits on the sample surface due to chloride corrosion and possibly be deteriorated by the overdosed CrFeB phase. This work can help us to design and prepare the highly corrosion-resistant Fe-based alloys.