Transmission and conversion electron Mossbauer study of crystallization of amorphous FeZrB alloys

The combined conversion electron emission and gamma-transmission Mossbauer spectroscopy are used to investigate the differences in the bulk and surface crystallization of the amorphous FeZrB alloy in which the nanocrystalline bcc-Fe phase was formed due to annealing. The measurements were performed for the ribbons in the as-quenched state, after Ih annealing at 430-600 degrees C and after short time annealing at 600 degrees C. The clear differences in the surface and bulk crystallization behaviours were detected. Not only the surface crystallization starts at lower annealing temperature than the bulk one, but additional phases were detected at the surface which do not form in the bulk. Structural transformations as a function of annealing time (15-120 s) are compared with those induced by 1 h anneals. The enhanced surface crystallization was attributed to the boron depletion of the surface region which leads to the decrease in the crystallization temperature at the surface.