Severe plastic deformation of copper: The state of grain boundaries and their triple junctions

The results of electron microscopic studies of the structure and phase composition of nanocrystalline copper produced during severe plastic deformation by torsion under high quasi-hydrostatic pressure are presented. Particular attention was focused on grain triple junctions. It is found that the triple junctions contain partial disclinations and secondary-phase particles. The strain dependences of the fraction of these triple junctions during formation of nanocrystalline copper are measured. Phase analysis of the structure of secondary phases is performed, and the sizes volume fractions of the secondary-phase particles are determined. The torsion-curvature of the crystal lattice appearing near triple junctions is measured. The problem of screening of the long-range field of stresses forming in triple junctions is discussed.