Atomic rearrangements and crystalline transformations in amorphous ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$

Atomic rearrangements and amorphous-to-crystalline transformations after isochronal annealing of as-quenched ${\mathrm{Fe}}_{81}$ ${\mathrm{B}}_{13.5}$ ${\mathrm{Si}}_{3.5}$ ${\mathrm{C}}_2$ (METGLAS® 2605SC) have been investigated by Mössbauer spectroscopy. The atomic rearrangements in the amorphous state consist of two major processes that depend on the annealing temperature. The first process is attributed to enhancement of the short-range order and the second one to the atomic rearrangements leading to crystallization. The crystallization was found to consist of at least two steps. In the first step, precipitation of Fe-4 at.% Si alloy takes place. The final crystalline products are Fe-7 at.% Si, ${\mathrm{Fe}}_2$B, and ${\mathrm{Fe}}_3$C. Just before crystallization occurs, the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer recoilless fraction, $f$, increases by 8%, and, after the completion of crystallization, the $f$ factor increases by 29%, both as compared to the as-quenched amorphous alloy.