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

Ordering Kinetics and Atomic Mobility in Ni3Al Intermetallic Compounds. Dimitrov, C., Dimitrov, O.: Defect and Diffusion Forum, 1997, 143-147, 251-6