Pressure and temperature dependence of nickel diffusion in Fe3Al:: Effect of ordering

The pressure and temperature dependence of Ni-63 heterodiffusion was investigated in the temperature range 888-1282 K, which includes the critical temperature of the A2-B2 order-disorder transition. Ali the experiments were carried out using the radiotracer method combined with a serial sectioning technique. The high-pressure measurements have shown that the diffusion process is controlled by monovacancies both in the ordered and disordered structures. The Arrhenius plot presents a downward curvature as the result of B2-type atomic ordering and the lattice diffusion coefficients can be fitted by a continuous curve as a function of temperature and long-range order parameter. Because of the site preference of Ni for alpha-sites, nickel diffusivity is slower and the activation energy of diffusion is higher than the corresponding values for iron self-diffusion. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.