DEFORMATION-BEHAVIOR OF [001]TI-56AL SINGLE-CRYSTALS

Specimens of an [001]-oriented Ti-56at.%Al single crystal were tested at room temperature (RT) and 873 K. The elevated temperature sample di splayed anomalous yield behavior, confirming the previous findings. Di slocation structures in the deformed samples at RT and 873 K, respecti vely, were observed by TEM. The micrographs for both RT and 873 K show long, partial dislocation loops of [101] superdislocations. However, dislocation dissociation behavior at the two temperatures was quite di fferent. At room temperature, the(101] dislocations dissociated into a 1/6[112] plus a 1/6[5 ($) over bar 14] dislocation connected by an SI SF, whereas at elevated temperature, a dissociation involving two 1/2[ 101] dislocations linked by an anti-phase boundary (APE) was observed. These observations suggest that at elevated temperature, a Kear-Wilsd orf or a ''roof-type'' barrier is responsible for the anomalous flow s tress. These results and their impact on the overall deformation behav ior of gamma titanium aluminides will be discussed.x