Intermétalliques sous chocs répétés : la transition ordre-désordre dans Fe-Al sous broyage à haute énergie

Abstract
Ball-milling of the ordered intermetallic compound Fe₅₀Al₅₀ is carried out in a calibrated vertical vibrating frame grinder at various temperatures T and milling intensities I : I is defined as the momentum transferred by the ball to the unit mass of powder per unit time. The long range order (LRO) parameter, as quantified by X-ray diffraction, decreases as a function of milling time and reaches a steady-state value which is a function of T and I. The time evolution of the LRO parameter can be fitted to a simple model of order-disorder transition under extemal forcing, in which the atomic exchanges occur because of two mechanisms : the forced atomics jumps, the frequency of which is found to be proportional to I and the thermaly activated jumps, the frequency of which is found to be a linear function of I. The forcing parameter, defined as the ratio of the latter two jump frequencies, is found to be the control parameter of the steady degree of LRO achieved under ball-milling. Moreover, the kinetic path of the LRO parameter depends on the milling intensity and milling temperature and is in semi-quantitative agreement with the model.