Institute of Metal Superplasticity Problems

We present analytical investigations of evolution of localized disturbances during their propagation in an infinite monoatomic nonlinear one-dimensional lattice, specifically the -Fermi-Pasta-Ulam (FPU) chain. We focus on two key disturbance characteristics: the position of the energy center and the energy radius. Restricting our analysis to long-wave low-amplitude disturbances, we investigate the dynamics in the -FPU chain and its two continuous versions described by the Boussinesq and Korteweg–de Vries (KdV) equations. Utilizing the energy dynamics approach and leveraging the known property of the KdV equation that any localized disturbance eventually decomposes into a set of non-interacting solitons and a dispersive oscillatory tail, we establish a similarity between the behavior of the disturbance in the linear chain and the nonlinear chain under consideration. Namely, at large time scales, the disturbance energy center propagates and the energy radius increases linearly in time, meaning dispersion also occurs at a constant velocity, analogous to the linear case. It was also found that, prior to its decomposition into non-interacting components, a disturbance in the KdV equation generally evolves as if subjected to an effective force from the medium. Furthermore, for two reduced versions of the KdV equation—one lacking the dispersive term and the other lacking the nonlinear term—the energy center of any disturbance moves with constant velocity. These results generalize the behavior observed in harmonic chains to weakly nonlinear systems and provide a unified framework for understanding energy transport.

The Ni45Mn36In14Co5 alloy was produced by the argon arc melting method. The application of a homogenization annealing process at 1173 K, followed by water quenching, resulted in the formation of a practically single-phase state. This particular state is referred to as the initial state. In the region of the structural transition, an abrupt change in magnetization is observed as the austenitic ferromagnetic phase transitions to the weakly magnetic martensitic phase. The magnetic entropy of ∆SM = -31.9 J/kg·K was obtained from thermomagnetic data in a magnetic field of 3 T. The reversible magnetocaloric effect ∆Tad = -0.7 K was observed in an alternating f = 0.2 Hz magnetic field of 1.8 T at the peak of the martensitic transformation. The maximum value observed during the initial application of the magnetic field is ∆Tad = -2.5 K. A study of the degradation of the magnetocaloric effect at the martensitic transformation temperature indicates that following 1400 cycles of magnetic field application, the ∆Tad value exhibits a 10% reduction, with a discernible ongoing trend. In conclusion, the alloy displays notable magnetocaloric effect values.

С использованием метода молекулярной динамики (МД) проведено исследование соединения двух нанокристаллических блоков меди путем знакопеременных взаимных смещений под действием приложенного давления, моделирующих процесс ультразвуковой сварки металлов (УЗС). Расчетная ячейка для моделирования состояла из двух блоков меди с колончатыми зернами размером 6.26 нм, имеющими общую ось колонны [112] и сечение в форме правильного шестиугольника. Поверхности блоков содержали неровности, описываемые синусоидой с амплитудой 10 Å. Система вначале релаксировалась под заданным давлением от 0.25 до 2 ГПа для достижения равновесия при температуре 300 К, затем блокам сообщались синусоидальные смещения с амплитудой 5 нм в противоположных направлениях. Моделирование показало, что соединение формируется путем расширения области контакта блоков при взаимных сдвигах последних, а первоначальная полость трансформируется в пору, размер которой уменьшается с повышением давления. При некотором критическом давлении происходит полное залечивание поры и образование сплошного соединения. Нанокристалл, образовавшийся в результате соединения, имеет повышенный атомный объем, что связано с релаксацией поры под действием сдвиговых деформаций и напряжения растяжения. Знакопеременная деформация сдвига, происходящая при моделируемой УЗС, приводит к росту зерен, в том числе путем объединения зерен, первоначально принадлежавших двум разным блокам. Это является важным фактором, приводящим к формированию бездефектного соединения при УЗС.

High-density electric current pulses increase the plasticity and reduce the yield stress of metals with negligible heat generation. This effect has great potential for the development of energy-saving technologies for processing hard-to-deform metallic materials. Despite the long history of the study of electroplasticity, there is still no consensus on the physical nature of this effect. In this paper, the effect of repetitive pulses applied at the same or gradually increasing tensile stress on the plastic deformation of copper wire is investigated using a home-made experimental setup. The electroplasticity of the wire in the delivery state and after annealing is compared. It is shown that for a constant tensile stress, the incremental plastic deformation of the wire decreases with each successive pulse. This effect is stronger for annealed wires because they have a lower dislocation density and therefore a lower plasticity resource. The Joule heat release in the specimen and the heating due to plastic deformation are evaluated. The results obtained will be used to fit the parameters of the atomistic model being developed to describe the interaction of electron flow with dislocations.

The paper presents the results of a study on the search for correct methods for measuring a high-value current pulse, which will be used to conduct research on the electroplastic effect. The electroplastic effect is the effect of electric current pulses on the plastic flow of metals. Electroplastic metal forming technology is a relatively new metal forming process that is energy efficient, environmentally friendly and versatile. In particular, it can be used to process metals or alloys that are difficult to process using conventional manufacturing processes. For the experimental study of the electroplastic effect, it became necessary to measure pulse currents of large magnitude, not only in amplitude, but also in the shape of the pulse. The pulsed current causes the formation of an alternating electromagnetic field near the conductors, so it can be measured with a Rogovsky current transformer. The results of the work present a schematic electrical diagram and a photograph with the appearance of an experimental installation for the study of the electroplastic effect. The results of measurements of the current value, the voltage drop on the sample and the dependence of the peak voltage values on the sample on the peak current value are shown. After making calculations and renormalising the data for the voltage drop on the sample according to the peak value of the current obtained on the transformer, the authors obtained the desired current values. The error of this method is estimated by calculating the total capacitance of capacitors, which does not exceed 2%.