Dislocation structures and deformation behaviour of Ti-50/52Al alloys between 77 and 1173 K

Coarse grained, binary alloys of Ti-50at.%Al and Ti-52at.%Al, containing low (approximately 250 wt.ppm) levels of interstitials, have been deformed in compression over a range of temperatures (77–1173 K). The resulting flow stress-temperature profiles in both the alloys consist of three distinct regimes: (I) 77–600 K (normal); (II) 600–1073 K (anomalous); (III) above 1073 K (normal). The fine structure of dislocations in the deformed samples was observed using weak-beam microscopy. It appears that the 12〈110] dislocations are the most difficult to move at 77 K and room temperature (RT). At low temperatures, deformation is controlled by twinning and the 〈011] superdislocations. The mobility of the 12〈112] dislocations is intermediate between the 〈011] and 12〈110] dislocations. As the deformation temperature increases, all the dislocations become relatively mobile, but the 〈011] dislocations become increasingly blocked as they adopt a thermally activated non-planar configuration and thereby give rise to a flow anomaly. Finally, at very high temperatures, the 〈011] superdislocations decompose to 12〈110] unit dislocations and 12〈112] superdislocations which are sufficiently mobile such that the strength decreases following the flow stress peak.