PLASTIC-DEFORMATION OF CHROMIUM-MODIFIED LL2AL3TI .2. WEAK-BEAM TRANSMISSION ELECTRON-MICROSCOPY STUDY OF DISLOCATION-STRUCTURES

Superdislocations on the [110]{111} system in single-crystal Al67Cr8Ti 25 have been studied using weak-beam transmission electron microscopy. It was found that the superdislocations are dissociated into superlat tice intrinsic stacking-fault-coupled 1/3[112] superpartials at 77 K b ut into antiphase-boundary (APB)-coupled 1/2[110] superpartials at 102 8 K. This transition in dislocation structure suggests that the APB en ergy decreases with increasing temperature, as has been suggested by o ther investigators. The shape of the critical resolved shear stress vs . temperature curve, which sharply decreases with increasing temperatu re at low temperatures and is almost temperature independent at high t emperatures, is also in agreement with this observation.