On the Critical Resolved Shear Stress and its Importance in the Fatigue Performance of Steels and other Metals with Different Crystallographic Structures

This study deals with the numerical estimation of the fatigue life represented in the form of strength-life (S-N, or Wöhler) curves of metals with different crystallographic structures, namely body-centered cubic (BCC) and face-centered cubic (FCC). Their life curves are determined by analyzing the initiation of a short crack under the influence of microstructure and subsequent growth of the long crack, respectively. Micro-models containing microstructures of the materials are set up by using the finite element method (FEM) and are applied in combination with the Tanaka-Mura (TM) equation in order to estimate the number of cycles required for the crack initiation. The long crack growth analysis is conducted using the Paris law. The study shows that the crystallographic structure is not the predominant factor that determines the shape and position of the fatigue life curve in the S-N diagram, but it is rather the material parameter known as the critical resolved shear stress (CRSS). Even though it is an FCC material, the investigated austenitic stainless steel AISI 304 shows an untypically high fatigue limit (208 MPa), which is higher than the fatigue limit of the BCC vanadium-based micro-alloyed forging steel AISI 1141 (152 MPa).

Goldenberry (Physalis peruviana L.) seed oil: press extraction, optimization, characterization, and oxidative stability

In order to optimize the screw-press extraction conditions of oil from goldenberry (Physalis peruviana L.) seeds obtained from nectar processing waste, a face centered design was applied. The oil was extracted at different temperatures (60, 80, and 100°C) and seed moisture contents (8, 10, and 12%). Oil recovery (OR) increased and residual oil in the cake decreased significantly as moisture content and temperature were reduced; oil moisture and volatile matter as well as acid value, K232, K268, and p-anisidine, respectively, decreased proportionally with the moisture extraction. Thus, the highest OR (86.4%) and the best quality were obtained at 8% moisture content and 60°C pressing temperature. Under these conditions, the extracted oil presented high linoleic acid (76.0%), iodine value (140.0 mg I2/g), and refractive index (1.4769). The oil stability index, measured by Rancimat, varied from 3.65 h (120°C) to 14.87 h (100°C); the predicted shelf life at 25°C was 120.4 days and the activation energy was 85.6 kJ/mol. The results highlighted that screw-pressing of goldenberry seeds provides quality oil without employing polluting and hazardous solvents.

NANOSIZED STRUCTURES IN PbTe MATRIX WITH CdSe IMPURITIES

В работе проведены электронно-микроскопические исследования полупроводниковых соединений на основе PbTe с примесями дисперсных фаз CdSe. Как показали результаты исследования, в исходном нелегированном соединении PbTe содержание атомов свинца составляет около 63,8 вес%, а содержание теллура составляет 36,2 вес%, т.е. соответствует стехиометрическому составу. Согласно изображениям электронного микроскопа, эти компоненты равномерно распределены по площади. Результаты исследования также показали, что образующиеся новые фазы имеют размеры зерен от 90 нм до 2 мкм. Полученные значения параметра решетки для соединения теллурида свинца и сингония хорошо согласуются с литературными данными. Структура образующихся фаз имеет такую же симметрию, как и исходное нелегированное соединение PbTe, гранецентрированную кубическую решетку с классом симметрии Fm3m. В молекулах новых образующихся фаз, в которых преобладают содержания элементов Cd и Se, обнаружено изменение сингонии кристаллической решетки. In this work, electron microscopic studies of semiconductor compounds based on PbTe with impurities of dispersed CdSe phases have been carried out. As shown by the research results, in the initial undoped PbTe compound, the content of lead atoms is about 63,8 wt.%, and the tellurium content was 36,2 wt.%, i.e. corresponded to the stoichiometric composition. According to the electron microscope images, these components are evenly distributed over the area. The results of the study also showed that the formed new phases had grain sizes from 90 nm to 2 pm. The obtained values of the lattice parameter for the lead telluride compound and crystal system are in good agreement with the literature data. The structure of the resulting phases has the same symmetry as the initial undoped PbTe compound, a face-centered cubic lattice with the Fm3m symmetry class. In the molecules of the newly formed phases, in which the abundances of the elements Cd and Se prevailed, a change in the crystal lattice syngony was found.

Synergetic effect of Si addition on mechanical properties in face-centered-cubic high entropy alloys: A first-principles study

High-entropy alloys (HEA) have been receiving increased attention for their excellent mechanical properties. Our recent study revealed that Si-doped face-centered cubic (FCC) HEAs have great potential to improve both strength and ductility. Here, we carried out first-principles calculations in cooperation with Monte Carlo simulation and structural factor analysis to explore the effect of Si addition on the macroscopic mechanical properties. As a result, Si addition increased the local lattice distortion and the stacking fault energy. Furthermore, the short-range order formation in Si-doped alloy caused highly fluctuated stacking fault energy. Thus, the heterogeneous solid solution states in which low and high stacking fault regions are distributed into the matrix were nucleated. This unique feature in Si-doped FCC-HEA induces ultrafine twin formation in Si-doped alloys, which can be a dominant factor in improving both strength and ductility.

THERMODYNAMIC PROPERTIES AND THE EQUATION OF STATE OF LEAD

Институт проблем химико-энергетических технологий Сибирского отделения Российской академии наук (ИПХЭТ СО РАН), г. БийскВысокотемпературное уравнение состояния (УС) твердого свинца с гранецентрированной кубической структурой решетки получено с использованием экспериментальных данных по термодинамическим свойствам, термическому расширению, сжимаемости, температурной зависимости модуля объемного сжатия. Весь объем экспериментальных данных оптимизирован с использованием температурно-зависящего УС Тайта в диапазоне давлений 0-130 кбар. Температурная зависимость термодинамических и термофизических параметров описана с использованием расширенной модели Эйнштейна. Полученное УС хорошо описывает весь объем экспериментальных данных в пределах погрешностей измерения отдельных величин. The high-temperature equation of state (US) of solid lead with a face-centered cubic lattice structure is obtained using experimental data on thermodynamic properties, thermal expansion, compressibility, and temperature dependence of the volume compression modulus. The entire volume of experimental data is optimized using a temperature-dependent Void in the pressure range 0-130 kbar. The temperature dependence of thermodynamic and thermophysical parameters is described using the extended Einstein model. The obtained US well describes the entire volume of experimental data within the measurement errors of individual quantities.