Strain-Hardening Stages and Structure Evolution in Pure Niobium and Vanadium upon High Pressure Torsion

High pressure torsion (HPT) is one of the ways to form nanostructured materials with high strength properties. However, HPT hardening mechanisms vary from material to material and are poorly understood for some BCC metals, particularly niobium and vanadium. This work aims to identify strain hardening stages for Nb and V metals during HPT. Two approaches have been used to identify the deformation stages during high pressure torsion. The approaches are based on the application of a "piecewise" model, taking into account the different deformation mechanisms that determine the type of the forming structure, and on the analysis of the hardness vs. true strain dependence according to the $H$$-$${e}^{0.5}$ law. We compared the identified stages with the results of the electron microscopic study of the structure. Both models describe well the structural changes observed microscopically in HPT-deformed niobium. However, we have shown that only the piecewise model gives an adequate description of the stages of structure development in vanadium. We have provided an explanation for the observed difference in the behavior of niobium and vanadium upon HPT.Comment: 21 pages, 9 figures, 1 tabl

Interpretation of the temperature dependence of the composition distribution in nanostructured alloys under severe plastic deformation

In the work, we analyze experimental data on the temperature dependence of the composition distribution in alloys under severe plastic deformation. The analysis is based on a simple model that combines the concepts of relay-race evolution of ajunction disclination network and structural-kinetic description of brittle fracture in view of quasi-hydrostatic compression. Conditions for a stable homogeneous steady-state plastic flow are considered and temperature-rate modes of plastic flow are determined in the context of deformation controlled by grain boundary diffusion or vacancy diffusion in the grain volume. © 2010