SOLID STATE AMORPHISATION OF A Fe-Co-Nb-B POWDER MIXTURE BY MECHANICAL ALLOYING

Fe61Co21Nb3B15 alloy was prepared from a powder mixture by mechanical alloying process in a high energy planetary ball mill P7. Structural and thermal changes of the milled powders were followed by X-ray diffraction (XRD), Mossbauer spectrometry and differential scanning calorimetry (DSC). Both XRD and Mossbauer spectrometry results reveal the formation, after 48 h of milling, of a highly disordered like amorphous structure where nanometer-sized iron borides were embedded. A mechanical recrystallisation process gives rise to the formation of alpha-Fe and alpha-FeCo nanograins on further milling. The occurrence of disordering in the milled powders may be confirmed by broad exothermic reaction in the DSC scans which consists of several overlapping exothermic peaks. Such behaviour originates from recovery, strain relaxation, grain growth and crystallisation.