Revisiting Cu-based shape memory alloys: Recent developments and new perspectives

Cu-based shape memory alloys belong to one important class of functional alloys, presenting shape memory effect and superelasticity due to their reversible martensitic transformation. Although they have been extensively studied since the middle of the last century, there are still many challenges to be solved. In the last decades, these alloys were extensively studied regarding new compositions, processing routes, phase transformation, mechanical and functional properties. Aspects of the thermoelastic phase transformation have been described using thermodynamic and thermo-mechanical studies, while the role of metallurgical features (such as grain size and morphology, ordering, precipitates and second phases) have been described mainly by phenomenological approach. In this sense this review discusses the advances in the general fundamentals of Cu-based shape memory alloys, the recent developments in processing routes, compositions, and applications in the last years. Graphical abstract

Effect of aging treatment on corrosion behavior of Mg-4Nd-2Gd-0.5Zr alloy

The effects of aging time on corrosion behavior of Mg-4Nd-2Gd-0.5Zr alloy in 3.5% NaCl solution were investigated by microanalysis, weight loss test and electrochemical test. The results show that the corrosion rate of Mg-4Nd-2Gd-0.5Zr alloy decreases first and then increases with the extension of aging time. Aging treatment alters the grain size and the distribution of the second phases. The second phases and grain size are the key factors affecting the corrosion rate of magnesium alloy. Among the tested alloys, the T6-8 h alloy shows the lowest corrosion rate, which is mainly attributed to the continuous distribution of second phases restricting the expansion of corrosion, hence the T6-8 h alloy showed the highest corrosion resistance. The corrosion rate of T6-16 h alloy increases obviously because of the growth of the grain size and the segregation of second phases, which accelerates the corrosion progress.

MILK PRODUCTIVITY AND TRUENESS TO TYPE OF BROWN SWISS COWS OF THE SMOLENSK REGION

Изучена молочная продуктивность коров бурой швицкой породы и определена ее производственная типичность в условиях Смоленской области. Исследования показали, что в породе преобладают животные молочного (36%) и низкомолочного (31%) типов, при этом высокомолочные коровы составляют 26% от всего поголовья. Рассчитанные усредненные значения коэффициента производственной типичности (КПТ) и индекса производственной типичности (ИПТ) находятся в пределах 3,00—3,99 ед., то есть изучаемых животных возможно отнести к классу молочных. Отмечено снижение значений результатов типичности от 1-ой к 3-ей лактации на 0,04—0,03 ед. (Р≤0,001).Экстерьер коров в зависимости от производственного типа имеет, в основном, недостоверную разницу между значениями промеров, но позволяет определить их соответствие типу. Следует отметить значительную разницу у коров всех лактаций глубины груди — 8,4—10,0 см (Р≤0,001), косой длины туловища — 5,6—8,2 см (P≤0,001). Интенсивность удоя в первую и вторую фазы лактации в зависимости от производственного типа увеличивается от 1-й к 3-й лактации. У коров всех производственных типов происходит снижение коэффициента устойчивости от 1-й к 3-й лактации и составляет 0,9—13,3%. Результаты коэффициента молочности постепенно увеличиваются от 1-й лактации к 3-й, кроме группы высокомолочных коров. Полученные данные обеспечат достоверность отбора лучших животных для дальнейшей селекции, повысят точность определения производственного типа, ускорят проведение оценки, поскольку для установления направления продуктивности животных целесообразно ее проводить по окончании 1-й лактации путем расчета КПТ и ИПТ. Итог — получение стад соответствующего направления продуктивности в зависимости от пожеланий собственника. The milk productivity of Brown Swiss cattle was studied and its trueness to type assessment was carried in the Smolensk region. The survey of the breed was showed that it is dominated by animals of the milk (36%) and low-milk (31%) types, while high-milk ones make up 26%. The observed average values of the trueness to type coefficient (TTC) and the index trueness to type of (ITT) are in the range of 3.00—3.99 points, that is, the studied animals may be classified as milk. There was a decrease the results to type from 1 to 3 lactation by 0.04—0.03 points (P≤0.001). The exterior of cows, depending on the production type, has mainly an unreliable difference between the values of body measurements, but what it allows to determine their compliance with the trueness to type. It should be noted a significant difference in the chest depth in all lactation 8.4—10.0 cm (P≤0.001), the oblique body length 5.6—8.2 cm (P≤0.001). The rate of production in the first and second phases of lactation, depending of the trueness to type, increases from 1 to 3 lactation. In all cow’s trueness to types, the coefficient of lactation stability decreases from the first to the third lactation and is 0.9 - 13.3%. The results of the milk yield coefficient gradually increase from 1 lactation to 3, except for the group of high-milk cows. The obtained results will ensure the reliability of the selection of the best animals for further breeding, increase the accuracy of determining the trueness to type, step up the assessment, since it is advisable to conduct it after the end of the first lactation by calculating the TTC and ITT to determine the direction of animal productivity. The result is the receipt of herds of the appropriate direction of productivity, depending on the wishes of the owner.

Study on the Strengthening Mechanism of Rare Earth Ce in Magnesium Alloys, Based on First-Principle Calculations and Electronegativity Theory

Since the commercial applications of rare earth magnesium alloys are increasing gradually, there are considerable advantages to developing lower cost and higher performance magnesium alloys with high abundance rare earth (RE) elements. However, the alloying order of a matrix magnesium alloy is completely changed with the addition of RE elements. Therefore, further study of the strengthening mechanism of Ce element in magnesium alloys is required. In this work, the thermodynamic stability of the possible second phases in a Mg-Al-Mn-Ce multicomponent magnesium alloy were analyzed, based on first-principle calculations, and the precipitation sequence of the key RE phases was deduced as a consequence. Combined with Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD), Energy Dispersive Spectrometer (EDS), and other experimental methods, it was investigated whether the preferentially precipitated second phases were the nucleation core of primary α-Mg. The complex alloying problem and strengthening mechanism in a multi-elemental magnesium alloy system were simplified with the aid of electronegativity theory. The results showed that the preferentially precipitated Al11Ce3 and Al10Ce2Mn7 phases could not be the nucleation core of primary α-Mg, and the grain refinement mechanism was such that the second phases at the grain boundary prevented the growth of magnesium grains. Moreover, the tensile test results showed that the reinforced structure, in which the Al-Ce phase was mixed with Mg-Al phase, was beneficial for improving the mechanical properties of magnesium alloys, at both ambient temperature and high temperature.

Phase Formation, Microstructure and Permeability of Fe-Deficient Ni-Cu-Zn Ferrites, (I): Effect of Sintering Temperature

We have studied the densification, phase formation, microstructure, and permeability of stoichiometric and Fe-deficient Ni-Cu-Zn ferrites of composition Ni0.30Cu0.20Zn0.50+zFe2-zO4-(z/2) with 0 £ z £ 0.06 sintered at temperatures from 900 °C to 1150 °C. The shrinkage is shifted from 1000 °C for z = 0 towards lower temperatures and reaches its maximum rate at 900 °C for z = 0.02. Stoichiometric ferrites show regular growth of single-phase ferrite grains if sintered at Ts ≤ 1100 °C. Sintering at 1150 °C leads to the formation of a small amount of Cu2O, triggering exaggerated grain growth. Fe-deficient compositions (z > 0) form Cu-poor stoichiometric ferrites coexisting with a minority CuO phase after sintering at 900–1000 °C. At Ts ≥ 1050 °C, CuO transforms into Cu2O, and exaggerated grain growth is observed. The formation of Cu oxide second phases is investigated using XRD, SEM, and EDX. The permeability of the ferrites increases with sintering temperature up to a maximum permeability of µ = 230 for z = 0 or µ = 580 for z = 0.02, respectively, at Ts = 1000 °C. At higher sintering temperatures, the permeability decreases, which is due to the formation of a microstructure with intra-crystalline porosity in large grains, and a non-magnetic Cu oxide grain boundary phase.

Dynamin deficiency causes insulin secretion failure and hyperglycemia

Pancreatic β cells operate with a high rate of membrane recycling for insulin secretion, yet endocytosis in these cells is not fully understood. We investigate this process in mature mouse β cells by genetically deleting dynamin GTPase, the membrane fission machinery essential for clathrin-mediated endocytosis. Unexpectedly, the mice lacking all three dynamin genes (DNM1, DNM2, DNM3) in their β cells are viable, and their β cells still contain numerous insulin granules. Endocytosis in these β cells is severely impaired, resulting in abnormal endocytic intermediates on the plasma membrane. Although insulin granules are abundant, their release upon glucose stimulation is blunted in both the first and second phases, leading to hyperglycemia and glucose intolerance in mice. Dynamin triple deletion impairs insulin granule exocytosis and decreases intracellular Ca2+ responses and granule docking. The docking defect is correlated with reduced expression of Munc13-1 and RIM1 and reorganization of cortical F-actin in β cells. Collectively, these findings uncover the role of dynamin in dense-core vesicle endocytosis and secretory capacity. Insulin secretion deficiency in the absence of dynamin-mediated endocytosis highlights the risk of impaired membrane trafficking in endocrine failure and diabetes pathogenesis.