MICROSTRUCTURAL AND KINETIC ASPECTS OF THE TRANSFORMATIONS INDUCED INA FEAL ALLOY BY BALL-MILLING AND THERMAL TREATMENTS

A Fe-40Al (at.%) alloy powder having a B2 ordered structure was milled in a high energy pla netary ball-mill. The microstructural evolution of the alloy was followed by analysing powder specimens milled for dif ferent times by X-ray diffraction, Mossbauer spectroscopy and magnetis ation measurements. Grain refinement and chemical disordering were the main transformations resulting from milling. A complete destruction o f the long-range order under the adopted conditions of milling was not achieved. From diffraction analyses it was possible to see how the co ncentrations of such defects as dislocations, planar faults, antiphase domain boundaries, etc., were modified by the heavy deformations invo lved with milling. Starting from the specimens milled for the longest time, considered in this study, isothermal annealing experiments were carried out to monitor the reverse transformations. The annealing temp eratures were selected on the basis of differential scanning calorimet ric and thermogravimetric magnetic measurements, which revealed that s everal transformations occur when treating the deformed powders. Recov ery and reordering take place at temperatures ranging from 100 up to 2 50 degrees C. A complete reordering is possible only at higher tempera tures, i.e. 700 degrees C, when recrystallisation is fully accomplishe d. (C) 1998 Acta Metallurgica Inc.