Moessbauer study of reordering of cold-worked iron-aluminum alloys

The process of atomic reordering of cold-worked Fe-Al alloys containing about 25 to 35at%Al during isothermal annealing has been investigated using Moessbauer spectroscopy. Moessbauer spectra from the specimens filed and annealed were observed at each stage of annealing and analyzed to obtain the distribution function of the internal magnetic field in the alloys. Furthermore, for the alloy with 24.9at%Al the information on the nearest neighbor configurations of constituent atoms could also be obtained directly from the Moessbauer spectra by assuming the Gaussian distribution function of hyperfine field acting on iron atoms with various number of iron neighbors, and the detailed process of reordering was clarified. The alloy with the DO3 type of order, which is either weakly magnetic or nonmagnetic depending on the composition, became strongly magnetic by filing. The alloy as-filed was much complicated in structure and the atomic configuration seemed to be distinctly different from that of the thermally disordered state. The alloy reordered very slowly in the course of annealing by way of perfect disorder and B2 type of order. The ordered alloy with B2 symmetry, which is nonmagnetic, was partially disordered by filing and changed into a weakly magnetic state. The alloy recovered promptly to its initial state by low temperature annealing. (author)