Interaction between dislocations and precipitates in an AlLi alloy

AlLi single crystals were annealed to contain precipitates of the ordered δ′ phase and have been deformed in situ in a high voltage electron microscope. Most of the dislocations move in pairs but single dislocations are also frequently observed. The obstacle distance and the curvature of bowed out segments of the leading dislocations of pairs, as well as the distance between the dislocations of the pairs were evaluated from the micrographs of dislocations under stress. The data are interpreted in terms of modulus hardening in addition to the order hardening. The single dislocations show approximately the same obstacle distance and curvature as the leading dislocations of pairs do. The experiments prove the generation of dislocations by the double cross-slip multiplication mechanism which leads to a loose arrangement of dislocations.