Microstructures of pyramidal slip dislocations in Ti3Al single crystals compressed along the C axis

The <<(11)over bar>26 >{11 (2) over bar 1} pyramidal slip in Ti3Al shows the so-called yield stress anomaly. A marked change in dislocation configuration is observed in the temperature range of anomaly; dislocations observed at -70 degrees C, the lowest temperature concerned, are ordinary pairs of superpartials coupled by the antiphase boundary (APE) and elongated mostly along the edge orientation. At the other extreme temperatures, e.g., 700 degrees C, pairs of unlike edge superpartials coupled by the APBs are observed. This change in dislocation configurations is interpreted as resulting from a change in mechanisms of dislocation generation depending on the deformation temperature; dislocations are generated as superdislocations in a lower temperature range and as superpartial dislocations in a higher temperature range. These observations are discussed in terms of the immobilization of edge c+a/2 superpartials by climb dissociation onto the basal plane following a reaction: 1/6 <(1) over bar (1) over bar 26 > -> 1/6 <(1) over bar 013 > + 1/6 < 0 (1) over bar 13 >.