Evolution of defect substructure in the Ni3Al alloy in the course of severe plastic deformation by torsion under pressure

Transmission electron microscopy was used to study the evolution of defect substructure in a Ni3Al-based alloy (Ni-18 at. % Al-8 at. % Cr-1 at. % Zr-0 .15 at. % B) in the process of severe plastic deformation by torsion under pressure. The crystal-lattice reorientation in the process of formation of an ultrafine-grained structural state was established to develop against th e background of a preliminarily formed highly imperfect substructure with a high crystal-lattice curvature and to be accompanied by the formation of d iscrete misorientation boundaries with a high effective density of partial disclinations. The high anisotropy of the displacement fields in the proces s of torsional deformation results in a significant structural (with respec t to the sizes of submicron grains) and crystallographic (with respect to t he directions of the vectors of discrete and continuous misorientations) an isotropy of the ultrafine-grained states that are developed. Based on exper imental data, a scheme of submicron-sized fragmentation on several structur al levels is constructed. Possible dislocation-disclination mechanisms of t he fragmentation are discussed.