PRESSURE AND TEMPERATURE-DEPENDENCE OF NICKEL DIFFUSION IN FE3AL - EFFECT OF ORDERING

The pressure and temperature dependence of Ni-63 heterodiffusion was i nvestigated in the temperature range 888-1282 K, which includes the cr itical temperature of the A2-B2 order-disorder transition. Ali the exp eriments were carried out using the radiotracer method combined with a serial sectioning technique. The high-pressure measurements have show n that the diffusion process is controlled by monovacancies both in th e ordered and disordered structures. The Arrhenius plot presents a dow nward curvature as the result of B2-type atomic ordering and the latti ce diffusion coefficients can be fitted by a continuous curve as a fun ction of temperature and long-range order parameter. Because of the si te preference of Ni for alpha-sites, nickel diffusivity is slower and the activation energy of diffusion is higher than the corresponding va lues for iron self-diffusion. (C) 1998 Acta Metallurgica Inc. Publishe d by Elsevier Science Ltd. Ali rights reserved.