Unloading yield point effects in iron aluminides

Strong yield point effects are observed on reloading iron aluminides after deforming, unloading for a short time at low temperatures, and reloading. Such yield point effects are shown to be essentially independent of material microstructure and occur so quickly at room temperature that it is unlikely that diffusional effects play any role. The most important factor determining the extent of yield point stress change at a given stress and temperature condition seems to be the Al content with aluminides of composition near FeAl showing very strong yield drops and aluminides of composition near Fe3Al hardly showing any yield point effects. The likely cause of the yield point effects is dislocation locking occurring during unloading, which is believed to be due to core transformation-dissociation at the a/2[111] dislocation cores. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.