Denis Alekseevich Aksenov

Within the framework of developing and refining minimally invasive medical techniques for restoring lost patient functions, research into bioresorbable materials represents one of the priority areas in the field of medical materials science. At present, the magnesium alloy of the Mg–Zn–Zr system, which exhibits good biocompatibility yet requires improvement in its combination of corrosion and mechanical properties, is regarded as a promising bioresorbable metallic material. In the present work, an investigation was carried out into the influence of the technological parameters of equal-channel angular pressing using the Conform scheme (ECAP–Conform) on the structure, mechanical properties and corrosion behaviour of the bioresorbable magnesium alloy grade MA14. Experimental work was conducted on long-length specimens, varying the number of ECAP–Conform passes and the deformation temperature. Based on the results of the study, it was established that the state obtained after four passes of ECAP–Conform exhibits the best combination of mechanical and corrosion properties. This state is characterized by a partially recrystallized structure with an average grain size of 9 ± 3 μm. X-ray diffraction analysis indicates a more than twofold increase in dislocation density, reaching 7.39∙10¹⁴ m⁻². Furthermore, a reduction in the intensity of the texture peaks corresponding to the prismatic planes {10–10} is observed. Mechanical tensile testing demonstrates an ultimate tensile strength of 310 ± 6 MPa and an elongation to failure of 26 ± 1 %. Gravimetric corrosion testing indicates a corrosion rate for the state after four ECAP–Conform passes of 6.6 mm/year at day 10 of testing.

В рамках разработки и совершенствования малоинвазивных медицинских методик восстановления утраченных функций пациентов исследования биорезорбируемых материалов входят в одно из приоритетных направлений в области медицинского материаловедения. На сегодняшний день к перспективным биорезорбируемым металлическим матери-алам относят магниевый сплав системы Mg-Zn-Zr, обладающий хорошей биосовместимостью, однако требующий при этом улучшения комплекса коррозионно-механических свойств. В данной работе проведено исследование влияния технологических параметров рав-ноканального углового прессования по схеме «Конформ» (РКУП-К) на структуру, механические и коррозионные свойства биорезорбируемого магниевого сплава марки МА14. Экспериментальные работы проводились на длинномерных образцах с варьированием количества циклов РКУП-К и температуры деформирования. По результатам работы было установлено, что наилучшей комбинацией механических и коррозионных свойств обладает состояние, полученное в течение четырех циклов РКУП-К (режим 2). Данное состояние характеризуется частично рекристаллизованной структурой со средним размером зерна 9 ± 3 мкм. Рентгеноструктурный анализ свидетельствует о более чем двукратном увеличении плотности дислокаций 7,39 × 1014 м-2. При этом также наблюдается снижение интенсивности текстурных пиков призматических плоскостей {10 – 10}. Механические испытания на растяжение свидетельствуют о достижении предела прочности 310 ± 6 МПа и относительного удлинения 26 ± 1 %. Гравиметрические коррозионные испытания свидетельствуют о скорости коррозии для состояния после четырех циклов РКУП-К до значения 6,6 мм/год на 10 день испытаний.

In this paper, the effect of deformation by equal-channel angular pressing (ECAP) and subsequent coating formation using various regimes (pulsed unipolar polarization—PUP and pulsed bipolar polarization—PBP) of plasma electrolytic oxidation (PEO) on the corrosion behavior of a bioresorbable Mg–Zn–Zr magnesium alloy was studied. Structural studies, gravimetric and electrochemical corrosion tests were performed to evaluate the alloy’s resistance to corrosion in Ringer’s solution. It was found that the use of ECAP contributes to structure refinement and a decrease in the corrosion rate, as compared to the initial state, to 7.6 ± 0.7 mm/year. The best corrosion resistance of the alloy in both the initial and deformed states is ensured by applying the PEO coating using the PUP regime; the corrosion rate was 2.8 ± 0.2 and 3.8 ± 0.4 mm/year, respectively. This may be due to the fact that this regime exhibits a higher content of the high-temperature forsterite Mg₂SiO₄ phase_. Electrochemical tests indicate a decrease in the corrosion current density for the PEO-coated samples by 3–4 orders of magnitude. ECAP processing leads to an increase in the polarization resistance to corrosion for the samples with a PEO coating produced in the PUP and PBP regimes.

In this work, the dependence of the change in structural characteristics and physical and mechanical properties of the Cu–0.6Cr–0.1Zr (wt %) alloy under high-pressure torsion (HPT) on the structural characteristics of the initial state—after quenching with a supersaturated solid solution and after aging with an ensemble of large micron-sized particles and a low concentration of the solid solution—was established. It is shown that, in the case of a quenched state with a supersaturated solid solution, changes in the physical and mechanical properties during the HPT process occur at the first stages of deformation (1–2 revolutions) and subsequently the values of properties stabilize. In the case of the initial state with an extremely low concentration of the solid solution and an ensemble of large particles, a nonmonotonic change in the physical and mechanical properties of the Cu–0.6Cr–0.1Zr alloy is observed, which is closely related to the initial shape, size, and distribution of particles in the material matrix.

In this work, the dependence of the change in structural characteristics and physical and mechanical properties of the Cu-0.6Cr-0.1Zr (wt.%) alloy under high-pressure torsion (HPT) on the structural characteristics of the initial state – after quenching with a supersaturated solid solution and after aging with an ensemble of large micron-sized particles and a low concentration of the solid solution – was established. It is shown that in the case of a quenched state with a supersaturated solid solution, changes in the physical and mechanical properties during the HPT process occur at the first stages of deformation (1–2 turns) and subsequently the property values stabilize. In the case of the initial state with an extremely low concentration of the solid solution and an ensemble of large particles, a non-monotonic change in the physical and mechanical properties of the Cu-0.6Cr-0.1Zr alloy is observed, which is closely related to the initial shape, size and distribution of particles in the material matrix.

Asymmetric rolling is a high-tech method based on the principles of severe plastic deformation. In the present paper, it is shown that Cu-0.8Cr-0.1Zr alloy is highly strengthened during asymmetric rolling due to structure refinement to an ultrafine-grained state. For example, in only one pass, at the accumulated strain 0.94 ± 0.20, the strength increases from 265 to 425 MPa. During the deformation process, the structure becomes refined, with the average size of fragments reaching 235 ± 90 nm. Structure heterogeneity is also observed in the cross section of a sample, which is associated with different rotation speeds of the rolls. The shape of grains in the central zone of samples corresponds to the state after conventional symmetric rolling. However, in the zone adjacent to the roll rotating at a higher speed, mechanical texture of grains is similar to that after shear. Subsequent aging of Cu-0.8Cr-0.1Zr alloy at 450°C makes it possible to achieve the ultimate strength 560 MPa and electrical conductivity 82% IACS, which exceeds the characteristics of the strengthened steel by 10–15%. The analysis of contributions to strengthening during asymmetric rolling reveals that the main contribution comes from the refinement of the grain structure to an ultrafine-grained state, which amounts to 58%. The fractions of the dislocation and dispersion contributions comprise 15 and 20%, respectively. Compared to conventional rolling, as well as other deformation methods that provide the same level of accumulated strain and strengthening in one cycle, such as equal channel angular pressing-conform, asymmetric rolling is the most promising due to its simpler process scheme.

В данной работе представлены результаты исследования влияния пластической деформации на структуру и свойства цинкового сплава Zn-0.8Li-0.1Mn. Эволюция структуры охарактеризована методами растровой электронной микроскопии (РЭМ) и EBSD. Обсуждаются диаграммы "напряжение – относительное удлинение", полученные при одноосном растяжении.