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 displayed anomalous yield behavior, confirming the previous findings. Dislocation structures in the deformed samples at RT and 873 K, respectively, 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 different. At room temperature, the 〈101] dislocations dissociated into a 16[112] plus a 16[514] dislocation connected by an SISF, whereas at elevated temperature, a dissociation involving two 12〈101] dislocations linked by an anti-phase boundary (APB) was observed. These observations suggest that at elevated temperature, a Kear-Wilsdorf or a “roof-type” barrier is responsible for the anomalous flow stress. These results and their impact on the overall deformation behavior of gamma titanium aluminides will be discussed.