Ordering kinetics and atomic mobility in Ni3Al intermetallic compounds

Atomic mobility was investigated in binary Ni3Al compounds with 24.6, 25.0 and 26.5 at% Al. It was determined by analysing the isothermal kinetics of atomic order relaxation induced by small deviations from equilibrium. Two kinetic processes are involved which could be fitted with pure exponentials. The relaxation rates are minimum at stoichiometry; the jump frequencies are in good agreement with extrapolated high-temperature diffusion data. The activation enthalpies of the two processes are the same within experimental uncertainty, and do not display a significant composition dependence. They are slightly lower than the sum of the vacancy formation and migration enthalpies and than the enthalpies for Ni self-diffusion in Ni3Al, reported in the literature.