Mössbauer Studies of Ordered and Cold-Worked Fe–Al Alloys Containing 30 to 50 at. % Aluminum

Abstract

Fe–Al alloys containing 30 to 50 at. % Al were investigated by Mössbauer spectroscopy. Both ordered alloys, having the CsCl or B2 structure, and alloys severely cold-worked by crushing were studied. At room temperature, all of the ordered alloys exhibit only paramagnetic lines, whereas the crushed alloys exhibit both paramagnetic and ferromagnetic lines, the intensity of the former increasing from 0% to 100% as the Al concentration increased from 30% to 50%. The results can be explained by considering the nearest neighbor configurations of Fe atoms in the ordered and deformed alloys, with slight corrections for next-nearest neighbors. Plastic deformation induces ferromagnetism by creating large numbers of antiphase boundaries across which the number of Fe–Fe nearest-neighbor bonds is significantly greater than in the ordered alloy. The observed percentages of paramagnetic and ferromagnetic material and the average effective field values in the crushed alloys indicate that the average linear dimensions of the antiphase domains are about six atomic distances. In addition, the effects of antiphase boundaries and short-range order produced by heat treatment have been observed in alloys of the DO3 structure (BiF3 type) having less than 25% Al.