Kinetics of short-range and long-rangeB2 ordering in FeCo

Short-range and long-range-order parameters were measured by Mössbauer spectrometry and x-ray diffractometry during the disorder →B2 order transformation in equiatomic FeCo. The change from a homogeneous mode of ordering at high temperatures to a heterogeneous mode of ordering at low temperatures was confirmed. By comparing parametric plots of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ hyperfine magnetic field versus long-range-order parameter for ordering in these two modes, an early independent relaxation of the short-range order was found in the kinetic path for homogeneous ordering. This relaxation was in reasonable agreement with estimates based on statistical kinetic theory.