Pit growth in a Ni-Nb metallic glass compared with its crystalline counterpart

The growth and repassivation behavior of metastable pits in a Ni50Nb50 metallic glass, as well as its crystalline counterpart, were investigated by statistical analysis on the current transients in potentiostatic measurements. The results show that amorphous Ni50Nb50 sample demonstrates a higher transient current, shorter pit growth and repassivation times than the crystallized sample. Comparisons of pit growth rates and charges passed during pitting reveal that pits in amorphous alloy grow faster but with smaller final pit volumes. It is suggested that amorphous structure can induce rapid dissolution in pits and thus promote the accumulation of passivating elements (Nb), resulting in a higher repassivation rate. A notable effect of amorphous structure on the early growth of pits is determined.