Evolution of defect substructure in Ni3Al alloy in the course of torsion under pressure

By the method of transition electron microscopy the evolution of defect substructure in Ni3Al base alloy (Ni-18 at. % Al-8 at. % Cr-1 at. % Zr-0.15 at. % B) was studied in the process of severe plastic deformation by torsion under pressure. It is ascertained that crystal lattice reorientation in the process of ultrafine grain (UFG) structural state is developed at the background of preliminarily formed highly defective substructure with a great curvature of crystal lattice, being accompanied by formation of discrete boundaries of disorientation with highly effective density of particle disclinations. Essential structural (submicrograin size) and crystallographic (directions of discrete and continuous disorientation vectors) anisotropy of UFG states formed as a result suggests a high anisotropy of displacement fields in the course of deformation by torsion. A scheme of submicrofragmentation of the lattice on several structural levels is provided on the basis of experimental data. The regularities revealed permit discussion of possible dislocation-disclination mechanisms of the fragmentation mentioned