Eduard Kozlov

Deformation behaviour of ultra-fine-grained copper

Abstract Mechanical behaviour and structural changes, such as the evolution of grain and dislocation structures and the formation of slip lines and grain-boundary-sliding traces, of a submicron-grained (SMG) copper during room-temperature compression have been studied. It is suggested that the absorption of dislocations into grain boundaries (GBs) is due to the migration and sliding of some highly non-equilibrium GBs during the deformation process and is influenced by high level internal stresses. From this point of view, the unusual behaviour of SMG copper, in particular, the high yielding and flow stresses, the absence of strain hardening, high plasticity and low strain rate sensitivity, are explained. Analogies of the mechanical behaviour of SMG copper with mechanical properties of metallic materials at large plastic strains in stage IV are discussed.

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.

Structure of triple junctions of grains, nanoparticles in them and bending -torsion in metal nanopolycrystals

The paper presents the results of the transmission electron microscopic (TEM) investigation of the structure and phase composition of nanocrystalline copper obtained by the severe plastic deformation using the high pressure torsion (HPT) method. Special attention is paid to the triple junctions of grain boundaries. It was established that the triple junctions contained the partial disclinations and particles of the secondary phases. The dependences of such junction fractions on the deformation were measured of the formation at nanocrystalline copper. The phase analyses of the secondary phase structure were carried out, the sizes of the phase particles and their volume fractions were determined. The bending – torsion of the crystal lattice arising near the triple junctions was measured. The problem of the long – range stress field screening was considered.

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.

Distribution of slip tracks in single crystals of Ni3Fe alloy

The results of an experimental investigation of the distribution of slip tracks in a primary system in single crystals of Ni3Fe alloy, oriented for a single slip, are presented. Investigations were carried out over a range of scales which differed by three orders of magnitude. Histograms of the distances between slip tracks at different scale levels are constructed. Self-similar track distributions in the primary slip system over the range of scales investigated are established.

Structural and Phase State of Fractured Rotor of High-Pressure Steam Turbine

The structural and phase state of the metal of a fractured rotor of a steam turbine is studied with the use of modern methods of physical research. The metal is shown to contain gradient structures. The cause of the failure of the rotor is established. The gradient structures are determined by the developed method of acoustic scanning.

High-current vacuum-arc ion and plasma source "Raduga-5" application to intermetallic phase formation

Phase composition, structural state, and mechanical properties of the ion-doped surface layers of Ni, Ti, and Fe targets with Al and Ti ions implanted into using the metal ion beam and plasma source Raduga 5 have been investigated. The high-intensity mode of implantation allowed us to obtain the ion-doped layers with the thickness exceeding the ion projected range by several orders of magnitude. By the transmission electron microscopy, it has been found that the fine-dispersed equilibrium intermetallic phases (Me3Al, MeAl) and the solid solution of aluminum were formed in the doped Ni, Ti, and Fe surface layers at the depth of up to 2600nm. The maximum dopant concentration reached 75%. It has been shown that the average size of the formed phases was of 70nm. The microhardness of the different target surface layers increased by 1.5–3 times. The wear resistance of the samples did not change within the temperature range of 300–700K.

Role of tension in microstructure formation in pure metals affected by ion implantation

Dislocation structures in the near surface layers of α-Fe produced by repetitively pulsed intense Hf ion beams with doses of 0.23 × 1016 to 24.0 × 1016 ions cm−2 were studied by electron microscopy. Both ion implantation and plasma deposition were used. Under such conditions the maximum impurity concentration of Hf in α-Fe appeared to be 70 at.%, the dose of implanted ions being determined from profile analysis of Hf distribution by the RBS method. A developed dislocation structure is formed by ion implantation in the near surface layer of α-Fe over a depth of 100 μm. The dislocation density reaches its maximum value at a depth of 5–7 μm from the surface and is increased by about 1–2 orders of magnitude from that in the initial state. Static tensions formed in the doped layer play a decisive role in the formation of the dislocation structure.

Structural and phase transformations in 0.3C-1Cr-1Mn-1Si-Fe steel after electrolytic plasma treatment

The paper presents the transmission electron microscopy (TEM) investigations on thin foils concerning phase transitions occurred in the type 0.3C-1Cr-1Mn-1Si-Fe alloyed steel after the electrolyte plasma treatment, i.e. carbonitriding at 850°C during 5u2005min. TEM investigations involve two points, namely: on the specimen surface and at 50u2005µm distance from the surface, i.e. in transition layer. It is shown that carbonitriding results in the formation of structures the properties of which are changed at a distance from it’s the specimen surface. Thus, the modified morphology of the steel matrix is represented mostly by high-temperature lamellar martensite on α-phase surface, while the intermediate layer is represented by massive martensite. After carbonitriding, the particles of the alloyed cementite and M2C0.61N0.39, M4(C,N), M7(C,N)3, M23(C,N)6 carbonitrides are observed in all layers inside α-phase crystals and at their boundaries. The concentration of carbon and nitrogen on the surface is considerably hig...