SUPERDISLOCATIONS AND THEIR RELATIVE STABILITY SINGLE-CRYSTAL TI-56ALDEFORMED AT 573 K

The core configurations of [(1) over bar 01] superdislocations in sing le crystal Ti-56Al have been investigated by high resolution electron microscopy. The results show that the dissociated superpartial disloca tions in deformed Ti-56Al at 573 K adapt two different configurations: (1) coplanar dissociation; and (2) rooftop type dissociation in which each coupling superpartial (1/2[(1) over bar 01]) lies in two differe nt {111} slip planes. The rooftop configuration appears to be formed b y a thermally activated process and provides the pinning of gliding su perdislocations at this temperature. The calculated elastic interactio n energy between the coupling superpartial dislocations in the anisotr opic medium shows that the rooftop configuration has lower interaction energy than that of the coplanar configuration. Based the observation and theoretical calculations, a model based on partial cross slip and its reversal is proposed for the anomalous hardening in the range of RT-650 K. (C) 1997 Elsevier Science Limited.