Sonia Azzaza

Solid state amorphisation of mechanically alloyed Fe-Co-Nb-B alloys

Fe 61 Co 21 Nb 3 B 15 powder mixture was prepared by mechanical alloying process in a high energy planetary ball mill. 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 amorphous-like structure where nanometer-sized iron borides were embedded. A mechanical recrystallisation process gives rise to the formation of α-Fe and α-FeCo nanograins on further milling. The occurrence of structural disorder in the milled powders might 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.