Two-level Nanostructural States in Metallic BCC-Materials after High-pressure Torsion in the Bridgman Anvils

Abstract

The results of an electron-microscopy investigation of two-level nanostructural states (submicrocrystals, measuring about 100 nm in size with the inner nanostructure and nanocrystal size about 10 nm, and crystal lattice curvature of hundreds of deg/μm) formed in the specimens of unalloyed Ta and V and Mo–Re-based alloys in the course of high-pressure torsion in the Bridgman anvils are generalized. A mechanism of their formation is proposed – quasiviscous motion of nanodipoles of partial disclinations, which is controlled by the flows of nonequilibrium point defects in the fields of high local pressure gradients. It is shown that the microstructure evolution with the increasing deformation degree consists in an increase in the volume fraction of a two-level nanostructural state, which results in a 3–4-fold increase in the microhardness of the deformed specimens, its maximum values being in the range Hμ ≈ (E/27–E/32). The principal physical factors and conditions of formation of these states upon plastic deformation of submicro- and nanocrystals are discussed.