THE DISLOCATION MICROSTRUCTURE IN ORTHORHOMBIC-O TI2ALNB DEFORMED BETWEEN ROOM-TEMPERATURE AND 800-DEGREES-C

Ti-26Al-21Nb (at.%) samples with the orthorhombic O structure, deforme d at various temperatures, have been analysed in order to determine th e sensitivity of their microstructures to the deformation temperature. The activation of [100] and 1/2 < 110] dislocations, and interactions between them, have been observed from room temperature to 800 degrees C. At high temperature, the activation of dislocations with [001] com ponent Burgers vectors has also been identified. The poor ductility in tension at room temperature is ascribed to an insufficient number of slip systems to accommodate the deformation. Attention is paid to the splitting modes and to the energies of the various planar defects invo lved in the dissociations.