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

Atomic rearrangements and crystallization within 100 nm of the surface in isochronally annealed amorphous ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$ (METGLAS® 2605SC) ribbons have been investigated by conversion-electron Mössbauer spectroscopy. The atomic rearrangements at the dull surface, at the shiny surface, and in the bulk of the ribbon are all different. The onset of crystallization at the two surfaces occurs at lower temperatures than for the bulk. In the amorphous state, the average atomic compositions are suggested to be different in the shiny-surface layer, in the dull-surface layer, and in the bulk. The crystallization was found to consist of three steps. In the first step precipitations of Fe-(∼2.0-3.0) at.% Si and Fe-(∼2.5-3.5) at.% Si take place at the shiny and the dull surfaces, respectively, and in the second step crystallization of ${\mathrm{Fe}}_3$C occurs. The process is completed by crystallization of ${\mathrm{Fe}}_2$B and a decrease of about 1% in the silicon concentration of the Fe-Si alloys.