SLIP BAND PROPAGATION AND SLIP VECTOR TRANSITION IN B2 FEAL SINGLE-CRYSTALS

At the peak temperature, 823 K, of the yield strength anomaly of B2 Fe Al, slip band propagation and slip vector transition were investigated using Fe-39 mol% Al single crystals. The single crystal oriented alon g a compression axis close to the [<(1)over bar 23>] direction showed serrated flow during work-hardening at small strains (<2%). Coarse sli p bands propagate in the single crystal specimens, like Luders band pr opagation in polycrystals, in the initial strain range. The slip vecto r was identified by TEM to be parallel to [111] in the early stage of strain corresponding to yielding. Beyond plastic strains of about 3%, serrations disappeared and significant work-softening occurred. The sl ip vector responsible for the later stage of deformation was observed to be [100]. That is, the slip vector changes from [111] to [100] as t he plastic strain increases. Because the density of [111] superdisloca tions is found to be very low after the slip transition, glide decompo sition of [111] superdislocations is believed to the primary source me chanism for [100] dislocations. The slip band propagation in B2 single crystals is discussed in comparison with that of other intermetallic single-crystalline materials. (C) 1998 Acta Metallurgica Inc. Publishe d by Elsevier Science Ltd. All rights reserved.