L. I. Trishkina

Thermodynamics of substructure transformations under plastic deformation of metals and alloys

The paper is devoted to behavior of the energy stored in deformed metals and alloys. The study is based on the well-known theoretical approaches and on the electron microscopy data obtained by the authors during investigation of the deformed Cu-Al and Cu-Mn f.c.c. alloys. Influence of the solid solution hardening value on the mechanisms of dislocation substructure evolution was studied. The accumulated energy for the substructure being formed at plastic deformation was evaluated. Ways of improvement of such evaluations were considered.

Features of Work Hardening of Polycrystals with Nanograins

The present work is devoted to the investigation of the influence of the grain size on the main mechanical characteristics of nanopolycrystals of different metals. The Hall-Petch parameter behaviour for Al, Cu, Ni, Ti and Fe was examined in the wide grain size interval. The stages of plastic deformation and the parameters of work hardening for nanocrystalline copper were analysed in detail. The deformation mechanisms and critical grain sizes accounting for the transition from the dislocation slip to the grain boundary sliding were described.

Internal field sources, their screening and the flow stress

Abstract The experimental investigation of the internal elastic stress fields in polycrystals of deformed Cu–Al and Cu–Mn alloys was carried out. The basic sources of the internal stress field were identified and the decrease of the field with increasing distance from the sources was determined. The average values of the internal stresses as a function of strain were measured. On this basis, the separation of sequences of dislocation substructure transformations into low-energy and the high-energy configurations was carried out.

Contact and barrier dislocation resistance and their effect on characteristics of slip and work hardening

Abstract The basic mechanisms of substructure hardening of network and cell dislocation structures were considered in terms of the quantitative data of the TEM investigation of foils and replicas. The comparative analysis of the barrier and contact dislocation resistance was carried out. These types of the dislocation resistance make the main contribution to the work hardening. Sharp distinction of the dislocation ensembles properties where the work hardening is determined by the relations τ∼ρ 1/2 and τ∼D − 1 was shown. The attention was paid on presence of the softening fluctuation contribution into the flow stress, which is increased with the increase of inhomogeneity of the dislocation distribution.

Evolution of the dislocation structure and the stage of work-hardening of Ni3Fe alloy with [001] orientation

Using transmission diffraction electron microscopy, the dislocation structure of work-hardened iron nickel alloy with the compression axis in [001] orientation is studied over a wide interval of gradual strain. A connection is established between the change of the flow curve and the type of substructure formed. The quantitative characteristics of the observed structural types are determined and their behavior at different stages of the strain curve is traced.

Geometrically necessary dislocations in FCC polycrystalline metallic materials on the mesoscale

The dislocation structure of deformed copper alloys doped with Mn and Al was determined by selected area diffraction (SAD), performed using a transmission electron microscope. The scalar dislocation density, the density of geometrically necessary dislocations, and the density of statistically stored dislocations were measured. Special attention was given to the size of grains. The effect of size on the accumulation of geometrically necessary dislocations was studied.

Storage of dislocations during plastic deformation of polycrystalline copper-manganese solid solutions

The regularities of dislocation storage during the deformation of homogeneous polycrystalline solid solutions with different degrees of solid-solution hardening have been studied and described. The effect of alloy concentration and test temperature is considered. The role of different dislocation density components (average scalar dislocation density, excess density, and dislocation density in walls and cells) is selected. Particular attention has been paid to the parameters of cellular substructure measured at different test temperatures and alloying concentrations. The important role of the solid-solution hardening in the regularities of dislocation storage is established.

Cellular dislocation substructures in polycrystals of FCC solid solutions based on copper: Holt’s relation and the size effect

The cellular dislocation substructures (CDSes) of Cu-Mn polycrystalline solid solutions upon plastic deformation is studied by means of TEM. It is determined that Holt’s relation holds for alloys with different grain sizes, solid solution concentrations, and deformation temperatures. The dependence of Holt’s coefficient C on the main polycrystalline parameters and deformation conditions is studied. Regularities of the fraction of closed cell boundaries and disoriented boundaries in CDS that emerge upon deformation are determined.

Hardening mechanisms and deformation stages in nanograined polycrystals

Strain hardening of nanograined polycrystals is studied using copper-based alloys as an example. The stages of strain hardening are compared for these alloys and for pure metals (copper, gold) having a similar grain size in the range 40–200 nm. The stress σ-strain ɛ dependence demonstrates that the strain hardening of these polycrystalline nanograined materials proceeds, as a rule, in three stages with different hardening mechanisms.

Stress-strain dependence and the evolution of dislocation structure in Cu-Mn polycrystalline concentrated solid solutions

Deformation of metallic materials results in dislocations occurrence and accumulation, with establishment of their definite distribution (dislocation substructure). The type of dislocation substructure (DSS) defines largely resistance to deformation and fracture of materials. Quantitatively the interrelation of DSSs and resistance to deformation are studied on a limited number of alloys. Foreign literature lacks studies referring to those issues. The given paper investigates the stress-strain dependences in Сu-Mn polycrystalline solid solutions. Mn concentration in the alloys varied within the range of 10...25 at.%. Polycrystals with 10 and 240 μm mean grain size were investigated. Deformation was applied by means of tension at the velocity of 2∙10 s and the temperature of 293 К. Using transmission electron microscope at the accelerating voltage of 125 kV, microstructure of the samples was investigated when they were deformed up to various deformation degrees. The types of DSSs were defined. The connection of the deformation stage under tension with the formed types of DSS was discussed. The sequence of transition of DSSs during the process of alloys deformation was defined. Appearance of the new stage of deformation hardening is attributed to the occurrence of the new type of substructure. The occurring “new” DSS develops during the deformation process, while “the old” DSS gradually disappears. Each of the stage of plastic deformation generally has two types of DSSs. The connection of the deformation stage and the strain hardening coefficient with the DSS was defined and it was shown to possess the definite dislocation density.