Slip band propagation and slip vector transition in B2 FeAl single crystals

Abstract

At the peak temperature, 823K, of the yield strength anomaly of B2 FeAl, slip band propagation and slip vector transition were investigated using Fe–39mol% Al single crystals. The single crystal oriented along a compression axis close to the [123] direction showed serrated flow during work-hardening at small strains (<2%). Coarse slip bands propagate in the single crystal specimens, like Lüders band propagation in polycrystals, in the initial strain range. The slip vector 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 slip vector responsible for the later stage of deformation was observed to be 〈100〉. That is, the slip vector changes from 〈111〉 to 〈100〉 as the plastic strain increases. Because the density of 〈111〉 superdislocations is found to be very low after the slip transition, glide decomposition of 〈111〉 superdislocations is believed to the primary source mechanism for 〈100〉 dislocations. The slip band propagation in B2 single crystals is discussed in comparison with that of other intermetallic single-crystalline materials.