Microstructural study of the low-temperature nanocrystallization of amorphous Fe78B13Si9

The amorphous Fe78B13Si9 (Metglas 2605S-2) alloy is treated by high current density electropulsing and the preliminary, partial, and full nanocrystallization can be achieved at temperatures lower than the bulk crystallization temperature by isothermal annealing. Analysis of Mössbauer spectra along with XRD measurement and TEM observation is presented. The preliminary crystalline product is the disordered b.c.c. Fe-based solid solution, probably containing a trace amount of B. In the partially and fully crystallized samples, α-Fe(Si), t-Fe2B, and also a small amount of t-Fe3B appear. The hyperfine magnetic field distribution P(H) of the residual amorphous phase in the crystallized sample takes a distinct bimodal type. It was suggested that the secondary peak at the higher field side can be associated with Fe-rich clusters in the residual amorphous phase of the preliminarily crystallized sample and that the lower field side is caused by the local segregation of some Si and B atoms in the residual amorphous phase excluded during the crystallization processes of the partially and fully nanocrystallized samples.