Mechanical properties of Fe70Al30 single crystals investigated by in situ straining experiments in a TEM

The mechanical properties of Fe-30at.% Al single crystals are studied by in situ straining experiments in a transmission electron microscope. These experiments are conducted in two temperature ranges: below and within the temperature range of the yield stress anomaly (YSA). Independently of the temperature range, the dislocations involved are identified as superpartial dislocations with a a/2[111] Burgers vector dissociated into two superpartials separated by an APE ribbon. They have a dominant screw character which is explained in terms of a frictional force. Their motion in the (110) plane is controlled by a Peierls type mechanism with two different average velocities: a slow one below and a fast one within the temperature range of the YSA. Associated with multiplication events, the latter is believed to correspond to microscopic plastic instabilities interpreted by a relaxation of the energy of the APE ribbon due to diffusion. (C) 1998 Elsevier Science S.A. All rights reserved.