Reordering a deformation disordered intermetallic compound by antiphase boundary movement

Long-range ordered intermetallic compounds can be disordered by severe plastic deformation and upon heating up the order is restored. A model for reordering is presented that considers recent TEM results showing that reordering is connected with the growth of antiphase boundary (APB) domains. The model is applied to the case of B2 ordered FeAl disordered by high-pressure torsion. The model makes use of the reordering peak observed by differential scanning calorimetry. The agreement between the vacancy migration enthalpy (H-V(M)) determined using a Kissinger plot and using the model, indicates that reordering occurs by the diffusion of vacancies along the APB. Also, the calculated size of the ordered domains during reordering agrees well with the experimental value. Furthermore, the model allows an estimation of material's parameters that are hard to access experimentally, e.g. the density of the vacancies at the APB (2 10(-2)) involved in reordering. By applying the model to FeAl reordered under high pressure, the model yields H-V(M) values effective for different pressures. The resulting low value of the vacancy migration volume supports the concept that reordering occurs by diffusion of vacancies along APB. Finally, the model demonstrates that by unloading a specimen deformed under high pressure, the density of vacancies active during reordering is significantly reduced (by about a factor of 2). (C) 2017 Elsevier B.V. All rights reserved.