No abstract

We have investigated the kinetics of the B2/DO 3 transition in Fe 3 AI (28 at. %) using in situ time-resolved x-ray scattering. In these experiments, the evolution of the diffuse and/or Bragg intensity near the (V/2 Y2 /2) DO superlattice peak is observed after the temperature of the sample is abruptly changed. H-ere we present results for the kinetics of re-equilibration of short-range order within the disordered (B2) phase, and of short-and long-range order within the ordered (DO1) phase. The short-range order is characterized by the diffuse peak intensity IDIFFUSE and correlation length ý; the long-range order is characterized by the Bragg intensity ARAGG. For quenches within the disordered phase, IDIFFusE and ý both relax exponentially at the same rate. The temperature dependence of the relaxation time shows evidence of a divergence at the critical temperature. For shallow quenches within the ordered phase, IAGG' 1OIFFUSE, and 4 all relax exponentially, but with different rates. However, for deep quenches within the ordered phase, IJIFFusE and ý do not show simple exponential relaxation. Instead, coarsening of short-range order into long-range order is seen, as in quenches from the disordered phase into the ordered phase. Investigation of up-quenches and down-quenches to the same temperature within the ordered phase indicates that disordering is faster than ordering.