ON THE MICROSTRUCTURE AND THERMAL-STABILITY OF RAPIDLY QUENCHED FE-B ALLOYS IN THE INTERMEDIATE COMPOSITION RANGE BETWEEN THE CRYSTALLINE AND AMORPHOUS STATES

The structure and the thermal stability of the Fe0.89B0.11 rapidly que nched alloy have been investigated. Transmission Mossbauer measurement s were carried out as a function of temperature in the range from 148 K to 513 K. Room temperature x-ray diffraction and transmission and co nversion-electron Mossbauer experiments, as well as 4.2 K spin-echo nu clear magnetic resonance measurements, were also performed after some selected thermal treatments for one hour between 523 K and 1273 K. Bas ed on these experiments it is suggested that the alloy is inhomogeneou s at nanoscopic scale and consists of a fine dispersion of a defective boride phase with an o-Fe3B-like short-range order, embedded in an al pha-Fe matrix. This result gives support to the models which indicate phase separation in the amorphous phase with o-Fe3B short-range order prevailing in the hypereutectic iron concentration range. This phase w as found to be less stable than the undefective one present in the les s boron concentrated alloys. The transformation into the equilibrium p hases, analyzed with an Arrhenius-type temperature dependence for the increase of the relative fraction of Fe2B, led to an activation energy E(a) = 1.38 +/- 0.68 eV/atom.