A transmission electron microscopy study of dislocation structures in a directionally solidified Ni3Al-based alloy deformed at 850 °C

Abstract

The dislocation structures present in a directionally solidified Ni3Al-base alloy after tensile testing in the [001] orientation at 850 °C have been studied using transmission electron microscopy weak beam techniques. Most dislocations are of the antiphase boundary pair type. Superlattice intrinsic stacking faults have also been observed, but they are rare. The 1/2〈110〉 dislocation pairs are present mostly with screw character. They are confirmed to be the Kear-Wilsdorf configurations. Non-screw segments of the 1/2〈110〉 dislocation pairs are dissociated on {111} planes. Movement of the 1/2〈110〉 dislocation pairs in {010} planes has been found to be the result of a thermal activation and interactions between the screw segments and the non-screw segments. It is suggested that deformation is mainly the result of the non-screw segments slipping in the {111} planes. As the 1/2〈110〉 dislocation pairs become screw oriented, they cross-slip onto the {010} planes and may sometimes bend in these planes. Thus, further movement of the non-screw segments in the {111} planes requires drawing back the screw segments from the {010} to the {111} planes.