Order-order relaxations in intermetallics

Order-order relaxation processes in high-temperature intermetallics occur after an abrupt change of temperature and are controlled by atomic migration in the almost perfect superstructure. The related experiments were carried out using systems being of technological interest and representing three common types of superstructures: L1(2) (Ni(3)Albased quasi-binaries), L1(0) (FePd, FePt) and B-2 (NiAl, FeAl). The corresponding Monte Carlo (MC) simulations of "order-order" kinetics involving the Glauber dynamics implemented with vacancy mechanism for atomic jumps were performed. The studies indicate a crucial role of antisite-easy-diffusion channels offered by particular superstructures in determining the character of "order-order" processes and their relationship to steady-state self-diffusion. Specific mechanisms of the relaxations in triple-defect B2-ordered binaries are discussed.