FORMATION AND STABILITY OF SATURATED BUNDLED STRUCTURE (SBS) IN TI3ALSINGLE-CRYSTALS CYCLICALLY DEFORMED BY DOUBLE PRISM SLIP

Formation and stability of deformation substructure in fatigued Ti3Al single crystals deformed by double prism slip were examined under diff erent applied strain amplitude (Delta epsilon). The specimens were ini tially fatigued at Delta epsilon = +/-0.2% or +/-0.3% for 1 x 10(4) cy cles and subsequently cyclically deformed after the change in Delta ep silon from +/-0.2% to +/-0.3% or from +/-0.3% to +/-0.2%. The saturate d bundled structure (SBS) was composed of the bundles with high densit y of edge dislocations aligning along [0001] and screw dislocations be tween the bundles were formed in specimens fatigued at initial Delta e psilon to the saturated stage. The bundles in the SBS were developed a nd expanded after the increase in Delta epsilon to +/-0.3%, while the rearrangement of screw dislocations occurred and some parts of the sat urated edge bundles were removed after the decrease in Delta epsilon t o +/-0.2%. The thermal stability of the fatigued substructure was exam ined in order to understand the formation process of edge dipoles and debris in the SBS. The change in the maximum shear stress amplitude an d the Bauschinger effect were also examined during cyclic deformation. (C) 1998 Acta Metallurgica me. Published by Elsevier Science Ltd. All rights reserved.