Process of Order-Disorder Transformation in Iron-Aluminum Alloys

Abstract

The process of order-disorder transformation during slow cooling and isothermal annealing in Fe–Al alloys has been investigated by means of X-ray diffraction. During slow cooling the ordering takes place through the two-phase state at a certain composition. while at other compositions it occurs as a single-phase transformation. The isothermal ordering proceeds by a nucleation and growth of the ordered phase, and under certain circumstances the precipitation of disordered phase takes place gradually in the course of annealing. The disordering into the two-phase state from an ordered single phase proceeds in two steps. The most plausible phase diagram of the Fe–Al system containing the two-phase regions, α+B2 and α+DO3, is proposed. The size of ordered domains is estimated from the widths of superlattice reflections, and its change during the order-disorder transformation is discussed.