Atom probe study of the crystallization process of an Fe_73.5Si_13.5B₉Nb₃Cu₁ amorphous alloy

The crystallization process of a melt-spun Fe_73.5Si_13.5B₉Nb₃Cu₁ amorphous alloy was investigated by atom probe field ion microscopy (APFIM). It was found that Cu-rich clusters were formed in the early stage of annealing of the amorphous alloy even below the crystallization temperature. Above the crystallization temperature, it was found that the crystallization of α-FeSi bcc solid solution occured independently of the crystallized fcc Cu particles. In the optimum annealing condition, Cu enriched fcc particles containing approximately 60 at% Cu were found to coexist with the α-FeSi solid solution and the B and Nb enriched amorphous phase. From these observations, it was concluded that the formation of Cu clusters in the early stage caused the inhomogeneity of the Fe concentration in the amorphous phase and this caused an increased density in the number of nucleation sites for the crystallization of the α-FeSi phase. Nb and B were excluded from the crystallized α-FeSi phase and enriched in the remaining amorphous phase. This led to the stabilization of the amorphous phase and hindrance of the growth of α-FeSi grains.