Magnetic observation of deformation substructure in cyclically deformed Fe3Al single crystals

Abstract

abstractFe–28.0 at% Al single crystals with the D03 structure were cyclically deformed in tension-compression mode at constant total-strain amplitudes (εt). At and less than εt ¼ 0:25%; the maximum stress increased rapidly with increasing number of cycles to 20, then remained constant during further cycling. In contrast, small cyclic softening appeared at and more than εt ¼ 0:30% between the initial and the final stages of cyclic hardening. The deformation substructure in cyclically deformed Fe3Al single crystals was observed by both transmission electron microscopy (TEM) and magnetic technique. From TEM observation, pairs of superpartial dislocations with Burgers vector (b) of 1/4[111] moved dragging a next-nearest-neighbour antiphase boundary (NNN-APB) in the cyclic softening stage, though four superpartials generally moved in a group in the initial hardening stage. The change in dislocation configuration from four- to two-coupled superpartials may ease the cross-slip event resulting in the dislocation rearrangement and the cyclic softening. The magnetic properties of cyclically deformed Fe3Al single crystals were examined by a vibrating sample magnetometer. In particular, magnetic anisotropy in the primary slip plane was evaluated by measuring high-field susceptibility in the approach to magnetic saturation at different directions of magnetic field. The cyclically deformed crystals exhibited strong magnetic anisotropy due to atomic rearrangement near NNN-APB and internal strain around screw dislocations. Two types of magnetic anisotropy were separated from each other by the Fourier transformation. In the cyclic softening stage, the amplitude of NNN-APB-dependent anisotropy rose abruptly between 102 and 103 cycles while that due to screw dislocations remained constant during fatigue. This suggested that a disordering of D03 phase due to fatigue did not occur in the softening stage. The maximum stress of Fe3Al single crystals exceeded the required for superpartial pairs to drag NNN-APB, resulting in the cyclic softening.