Georgy Raab

Due to the ever-increasing demands of the construction, mechanical engineering, automotive, and other industries, materials engineers are exploring ways to improve the structure and properties of materials by changing their chemical and phase composition. However, one of the strategies for achieving high mechanical characteristics of the material is to select the processing parameters of the material, providing the required structure and properties without changing the chemical composition. Currently, one of the most promising technologies for obtaining the required structure and properties of a material is asymmetric rolling. The mechanics of gradient nanomaterials laboratory of the FSBEI HE Nosov Magnitogorsk State Technical University has implemented asymmetric rolling of aluminum alloy D16 on an industrial laboratory rolling mill 400, which is a unique scientific unit. The presence of an individual drive of the working rolls allows for the implementation of asymmetric rolling processes with the maximum possible ratio of speeds of the working rolls V1 /V2 = 1/10. The results of experimental studies of symmetrical and asymmetric rolling of aluminum alloy D16 on the mill 400 with mismatch speeds of working rolls V1 /V2 = 2/10 are presented. Using computer modeling, studies have been carried out to obtain patterns of thermal fields and the stress-strain state in the deformation zone. It has been revealed that the D16 alloy sheet in the annealed state demonstrates high technological plasticity during cold asymmetric rolling. A microstructural analysis of D16 alloy samples obtained by symmetric and asymmetric rolling at room temperature and relative deformation of 87% has been carried out. The patterns connecting the parameters of the structure with the processing parameters are established. Conclusions are drawn based on the research results.The research was carried out with the financial support of the Russian Science Foundation grant (Agreement No. 23-79-30015).

The problem of the real existence of the electroplastic effect during deformation of metallic materials of different nature is still relevant. At the same time, the influence of structure refinement is not considered enough. In this work, the deformation behavior of ultrafine-grained (UFG) titanium Grade 4 is compared with that of coarse-grained (CG) titanium under tension with pulse current of the low duty cycle. The deformation curves of both structure states are presented for different regimes of pulsed current and thermal heating from an external source. Structure studies by optical and scanning electron microscopy, as well as microhardness measurements have been carried out. It is shown that Grade 4 titanium under tension accompanied by pulsed current exhibits electroplastic effect (EPE) in the form of a flow stress reduction. EPE in UFG state is much stronger than in CG state. An increase in the density and duration of the current pulse leads to a multiple decrease in the flow stresses in CG and UFG titanium. The contribution in the flow stress reduction from heating by an external source was less than that from tension with pulse current at the same temperatures. The impact of pulsed current during tension does not influence microhardness and grain size.

Эффективным подходом к повышению сопротивления усталости металлических изделий является создание на поверхности изделия сжимающих остаточных напряжений с помощью его обработки методами поверхностного пластического деформирования (ППД). Один из эффективных методов ППД – процесс безабразивной ультразвуковой финишной обработки (БУФО). Также известным подходом к повышению механических характеристик, в том числе усталостного сопротивления, является создание в изделии ультрамелкозернистого (УМЗ) структурного состояния. Настоящая работа посвящена исследованию с помощью конечно-элементного анализа напряженно-деформированного состояния УМЗ-заготовки, подвергнутой ППД методом БУФО. В качестве материала заготовки выбран технически чистый титан марки Grade 4 в УМЗ-состоянии, полученный методом равноканального углового прессования по схеме «Конформ» (РКУП-К). В ходе исследования проведен анализ напряженно-деформированного состояния очага деформации после однократного удара индентора с последующей разгрузкой в упругопластической постановке задачи. Рассмотрено влияние амплитуды колебаний индентора и его геометрических характеристик на радиальные остаточные напряжения, в том числе глубину их залегания, среднее нормальное напряжение и интенсивность деформации. Установлено, что с увеличением радиуса индентора снижается значение интенсивности деформации (e). Характер распределения параметра e – градиентный, с уменьшением значений от поверхности к центру заготовки. Анализ результатов моделирования показывает, что радиальные остаточные напряжения в области очага деформации являются преимущественно сжимающими и, соответственно, позволят повысить сопротивление усталости готового изделия. Выявлено, что с увеличением амплитуды колебаний индентора возрастают и значения сжимающих радиальных остаточных напряжений – их максимум достигает 540 МПа при амплитуде 75 мкм с глубиной залегания этих напряжений до 0,3 мм. Увеличение радиуса индентора, т.е. фактически площади контакта, ведет к повышению величины сжимающих радиальных остаточных напряжений, причем практически линейно.

Nowadays, there is a great demand for increasing the strength and corrosion resistance of magnesium alloys for their wider use in machine engineering, oil industry, and medicine. This paper is devoted to a study on the effects of the combined process of reduction and equal channel angular pressing, as well as the subsequent ultrasonic irradiation on the structure, strength, and corrosion properties of the Mg-Al-Zn alloy. Deformation processing results in an increase of the strength up to 280 ± 10 MPa. A fine-grained structure is formed with a grain size of 10–20 µm and small recrystallized grains 1–2 µm in size. The corrosion resistance in the HCl medium falls down significantly. Action of ultrasound on the deformed specimen leads to an increased fraction of high-angle boundaries, in particular, the fractions of special, fully overlapping Σ13a boundaries and twin boundaries of Σ15b and Σ17a systems. Due to the ultrasonic treatment, the strength of the Mg-Al-Zn alloy increases up to 310 ± 5 MPa, while the corrosion resistance in HCl almost doubles.

The effect of severe plastic deformation by the conforming process of equal channel angular extrusion (ECAE-Conform) followed by cold rolling on the microstructures developed in a Cu-0.1Cr-0.1Zr alloy was investigated. Following the ECAE-Conform of 1 to 8 passes (corresponding strains were 0.8 to 6.4) cold rolling to a total strain of 4 was accompanied by substantial grain refinement and strengthening. An average grain size tended to approach 160 nm with an increase in the rolling reduction. An increase in the ECAE-Conform strain promoted the grain refinement during subsequent cold rolling. The fraction of the ultrafine grains with a size of 160 nm after cold rolling to a strain of 4 increased from 0.12 to 0.52 as the number of ECAE-Conform passes increased from 1 to 8. Correspondingly, the yield strength increased above 550 MPa. The strengthening could be expressed by a Hall–Petch type relationship with a grain size strengthening factor of 0.11 MPa m^0.5.

The quantitative concentration of alloying elements in low-alloyed copper alloys is an important factor in forming electrical and mechanical characteristics. It is known that severe plastic deformation is accompanied by both a substantial refinement of the structure and changes in the kinetics of phase transformations during the deformation and the post-deformation thermal treatment. This paper presents the results of a comparative analysis of the Cu–0.2Cr and Cu–1.1Cr alloys subjected to equal-channel angular pressing at room temperature. The analysis was performed for the grain structure, solid solution, and second-phase particles using transmission electron microscopy, scanning electron microscopy, X-ray crystal analysis, and the small-angle diffraction method. It was found that the level of structure refinement and mechanical characteristics after equal-channel angular pressing was almost the same for both studied alloys. Post-deformation aging of the Cu–0.2Cr alloy leads to the development of polygonization and re-crystallization within it. The aging of the Cu–1.1Cr alloy shows a better thermal stability than that of the Cu–0.2Cr alloy. In the Cu–1.1Cr alloy, after aging, in comparison with Cu–0.2Cr, a denser-packed ensemble of fine particles with an average size of 54 ± 2 nm is formed. In this case, the average size of fragments is 270 ± 15 nm and the ultimate tensile strength reaches 485 MPa.

The article considers evaluation of torsional strength and fracture of austenitic corrosion-resistant steel 08Kh18N9 with an ultrafine-grained (UFG) and co

In the present study, a coarse-grained Cu–0.5 wt% Zr alloy was repeatedly processed by a novel technique of rotational constrained bending (RCB). In this technique, the workpiece was deformed by bending in a channel with an angle of 90°, using a rotating roller. The influence of the number of passes (N) of RCB on strain distribution, microstructure evolution and mechanical properties of the alloy was investigated. The heterogeneous distribution of the microhardness in the billet cross-section after the first pass was transformed into a homogeneous one after twelve passes, due to the rotation of the sample by 90° clockwise between individual passes. In addition, the gradual refinement/homogenization of the microstructure and formation of strong (110) crystallographic texture were found with increasing N. The initial grain size of 180 μm decreased down to 3.4 μm after twelve passes. The dislocation density increased by two orders of magnitude after RCB processing. In accordance with the grain-size refinement and the strong increase of the dislocation density, RCB processing significantly enhanced the strength of the alloy, while the ductility considerably decreased. The yield stress increased from 63 to 524 MPa, while the elongation to failure decreased below 10% after twelve passes.

This work considers the development and the application of combined severe plastic deformation (SPD) techniques to produce contact wire with an enhanced complex of physical, mechanical, and service properties used for high-speed railway lines. This type of processing can be used as an alternative to most conventional production methods, including rolling and drawing. The proposed technique is based on the combination of radial swaging and equal-channel angular pressing, bundled with the wire-forming process. Laboratory contact wire samples with an enhanced complex of physical, mechanical, and service properties were produced during physical experiments. The composition of processed alloy samples meets modern requirements for contact wires for high-speed railways. Ultimate tensile strength of 560 ± 20 MPa, electrical conductivity of 76 ± 2% IACS, and relative tensile elongation of 20 ± 2% are achieved through the formation of a band structure. Fragments of 300 ± 20 nm were formed inside strips with the precipitation of secondary phase particles of 20–100 nm along the fragment boundaries, mainly during the aging process.