Papers by Author: Igor V. Alexandrov

Abstract: The composite filament structure was produced in the Cu-5.7%Cr and Cu-12.4%Cr as-cast alloy ingots by using equal channel angular pressing (ECAP) at room temperature. Optical and TEM microstructure, micro-hardness, tensile strength and electrical conductivity of ECAPed samples were investigated. The rotation and spreading of Cr particles took place during ECAP, and resulted in long thin in-situ filaments. The tensile strength increased with the number of the ECAP passes. A strengthening model was recommended to predict the enhancement of the tensile strength in Cu-Cr in situ fibrous composites.

Abstract: The effect of aging treatment on mechanical properties and electrical conductivity of Cu-5.7%Cr in situ composite produced by equal channel angular pressing (ECAP) was investigated here. The rotation and spreading of Cr particles was observed in Cu-5.7%Cr alloy during the ECAP, resulting in long thin in situ filaments. The equiaxed grains of the Cu phase with an average size of 200 nm were developed after eight passes of ECAP. When aging at 400~450 °C for 1 h, Cu-5.7%Cr composite after ECAP shows the maximum microhardness, and the electrical conductivity is larger than 70% of IACS. At 400 °C, the peak aging time appears for 0.5~2 h, dependent on the pre-strain for all ECAP samples. With the increase of ECAP passes, the enhancement of tensile strength due to the aging treatment declines, and even shows negative after eight passes of ECAP. The combination of ECAP and aging treatment would be a promising process to balance mechanical properties and electrical conductivity of Cu-5.7%Cr composite.

Abstract: Microstructure, mechanical properties and electrical conductivity in Cu-0.73%Cr alloy after HPT process and the subsequent aging treatment have been investigated. Ultrafine grained structure with the grain size ~150 nm has been achieved after the HPT and the subsequent aging treatment. Ultrafine grains with some growth twins were preserved in the overaged state, showing high thermal stability. The peak microhardness and tensile strength of Cu-0.73%Cr alloy after the HPT was found at 480 °C for 2 hours. Electrical conductivity shows an increase trend in the different aging states.

Abstract: Basing on the kinetic modeling, the role of microstructure peculiarities in formation of a revealed experimentally high-strength state of the nanostructured Al 6061 (Mg 0.8…1.2, Si 0.4…0.8, Cu 0.15…0.40, Cr 0.15…0.35, Mn 0.15, Fe 0.7, Zn 0.25, Ti 0.15 wt. %) alloy was analyzed, Possible strengthening mechanisms of the alloy subjected to high pressure torsion at room temperature have been considered. It has been shown that the grain size and segregation of Si, Cu and Mg atoms from the solid solution in the grain boundaries area are the main factors that enhance the alloy strength. Conclusions on the deformation mechanisms acting in the considered alloy have been made. They can be helpful for predicting the mechanical properties of materials. Quantitative estimation of the dislocation density, the stress of dislocation strengthening, and the stress of dislocation pinning by Mg atoms has been made.

Abstract: The initial and deformed states of austenitic stainless steel AISI 321 before and after neutron irradiation with a damage dose up to 5.3 dpa at reactor core temperature of 350 °С were comparatively investigated. Corrosion behavior, mechanical properties are analyzed in the temperature range of 20…650 °С. It is shown that radiation damage of the steel in the deformed state significantly decreases in comparison with the initial coarse-grained state at the same level of corrosion resistance.

Abstract: The high-strain-rate response of ultra-fine-grained (UFG) copper fabricated by equal channel angular pressing (ECAP) has been characterized by Split Hopkinson Pressure Bar (SHPB) test and quasi-static compression test has also been performed for comparison here. In the result of quasi-static tests a maximum yield stress equal to 432 MPa has been reached, at the same time the corresponding value turned out to be 995 MPa after a dynamic loading with the strain rate equal to 1700 s-1. It has been demonstrated that the strain rate sensitivity coefficient (m) has enhanced from 0.026 (coarse-grained copper) to 0.037 (UFG copper). Microstructure has indicated a high dislocation density and deformation twins inside the grains formed after a high-strain-rate deformation, which resulted in a high flow stress. The occurrence of a dynamic recrystallization has also been observed in the UFG copper subjected to high-strain-rate deformation. This has become apparent as an accelerated thermal softening and inherent instability typical for the UFG structure. Absence of adiabatic shear bands pointed out that UFG copper can be subjected to a dynamic impact without any fracture.

Abstract: A grain size is known to be one of the factors which define mechanical properties of metallic materials. At the same time the mechanisms which regulate the deformation behavior of bulk ultrafine-grained (UFG) metals produced by the severe plastic deformation method are still a subject for intensive study and fixed ambiguously. The report presents the developed model and the results of its application for kinetic modeling of the deformation behavior of coarse-grained (CG) and UFG Ti. Modeling has been carried out considering the possible contribution of dislocation slip and ageing. Conclusions about the role of the investigated mechanisms in the appearance of the peculiarities of the deformation behavior of CG and UFG Ti have been made.

Abstract: This paper presents the research results of the grain refining effect on the ductile-to- brittle transition temperature (DBTT) of commercial purity tungsten. The as-received tungsten was subjected to eight passes of equal-channel angular pressing (ECAP) at decreasing temperatures from 1300 to 1150 °C. According to optical and TEM microscopy the average grain size was refined considerably from ~80 μm to ~1 μm. The mechanical tensile tests, carried out at various temperatures for the tungsten samples, showed that DBTT decreased approximately 80 °C as a result of microstructure refinement by ECAP, at the same time the strength also increased 50-100 % by grain refinement. SEM observation of the fractures confirmed the mechanical testing results.

Abstract: The composite filament structure was produced in Cu-5.7%Cr as-cast alloy ingots, subjected to equal channel angular pressing (ECAP) and cold rolling (CR) at room temperature. Microstructure, tensile properties and electrical conductivity before and after the severe plastic deformation (SPD) processing have been investigated here. The results point out that the rotation and spreading of Cr particles took place during ECAP and the additional rolling resulting in long thin in situ filaments. The average grain size of a Cu phase is equal to about 200 nm after eight ECAP passes. The formation of finer equiaxed grains of the Cu phase has been revealed after the additional CR. The tensile strength 403 MPa and 507 MPa have been achieved after one and eight ECAP passes respectively and increased up to 517 MPa and 607 MPa after the subsequent CR deformation. The enhancement of the tensile strength and the deterioration of the electrical conductivity have been explained by the microstructure evolution of Cu matrix and the dendritic Cr phase.

Abstract: This paper presents the results of experimental X-ray structural analyses of both the evolution structure and the crystallographic one in the volume of Ti samples, subjected to the Severe Plastic Deformation (SPD), realized by torsion under high pressure equal to 6 GPa at temperature 298 K. The investigations have been carried out on the disk-shaped samples with the radius of 20 mm in an initial state (the as-received state) and in the states after 0.1, 0.5, 1 and 5 rotations by High-Pressure Torsion (HPT). In the result the evolution mechanisms of the general X-ray patterns, the volume fraction of phases, the character of preferred orientations, as well as the activity of various slip and twinning systems in α- and ω-phases, depending on the SPD degree have been found out. The received results allow explaining and forecasting the behavior of nanostructured Ti, considering the parameters of its microstructure and crystallographic texture.