Transmission electron microscopy was used to study the evolution of defect substructure in a Ni3Al-based alloy (Ni-18Al-8Cr-1Zr-0.15at%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 the background of a preliminarily formed highly imperfect substructure with a high crystal-lattice curvature and to be accompanied by the formation of discrete misorientation boundaries with a high effective density of partial disclinations. The high anisotropy of the displacement fields in the process of torsional deformation results in a significant structural (with respect to the sizes of submicron grains) and crystallographic (with respect to the directions of the vectors of discrete and continuous misorientations) anisotropy of the ultrafine-grained states that were developed. Based on experimental data, a scheme of submicron-sized fragmentation on several structural levels was constructed. Possible dislocation-disclination mechanisms of the fragmentation were discussed.

Evolution of Defect Substructure in the Ni3Al Alloy in the Course of Severe Plastic Deformation by Torsion under Pressure. Tyumentsev, A.N., Tretyak, M.V., Pinzhin, Y.P., Korotaev, A.D., Valiev, R.Z., Islamgaliev, R.K., Korznikov, A.V.: Physics of Metals and Metallography, 2000, 90[5], 461-70