ВЯЗКОСТЬ ВЫСОКОЭНТРОПИЙНЫХ РАСПЛАВОВ Cu–Sn–Pb–Bi–Ga, Cu–Sn, Cu–Pb, Cu–Ga, Cu–Bi ЭКВИАТОМНЫХ СОСТАВОВ

Temperature dependences of kinematic viscosity of high-entropy melts (HEM) of the composition, at %: Cu–20Sn–20Pb–20Bi–20Ga, Cu–50Sn, Cu–50Pb, Cu–50Ga, and Cu–50Bi are investigated in a temperature range from 1550 to 1300 °C. It is shown that melt overheating above a definite temperature (thom) leads to the appearance of viscosity hysteresis, which indicates the variation in the structural state of the HEM.  Values of thom for all studied samples are in limits of 925–1185 °C. It is found that heating of the HEM to definite temperatures (t*) leads to the variation in activation energy of viscous flow (Е) and entropy multiplier (A) in the Arrhenius equation: v = Aexp[E/(RT)]. Entropy of viscous flow (ΔS≠) for studied HEM is investigated in terms of the Airing theory. It is revealed that the magnitude of ΔS≠ for a five-component Cu–Sn–Pb–Bi–Ga melt in a cooling mode is smaller than during heating by a factor of 2,6. The found rheological characteristics of HEMs allow us to consider these melts as promising functional materials: solders, heat carriers, electric contacts.Исследованы температурные зависимости кинематической вязкости высокоэнтропийных расплавов (ВЭР) состава, ат.%: Cu–20Sn–20Pb–20Bi–20Ga, Cu–50Sn, Cu–50Pb, Cu–50Ga, Cu–50Bi в интервале температур от 1550 до 1300 °С. Показано, что перегрев расплав выше определенной температуры (tгом) приводит к появлению гистерезиса вязкости, что свидетельствует об изменении структурного состояния ВЭР. Значения tгом для всех изученных расплавов находятся в пределах 925–1185 °С. Обнаружено, что нагрев ВЭР до определенных температур (t*) ведет к изменению энергии активации вязкого течения (Е) и энтропийного множителя (A) в уравнении Аррениуса: v = Aexp[E/(RT)]. В рамках теории Эйринга проведена оценка величины энтропии вязкого течения (ΔS≠) для изученных ВЭР. Выявлено, что для 5-компонентного расплава Cu–Sn–Pb–Bi–Ga величина ΔS≠ в режиме охлаждения в 2,6 раза меньше, чем при нагреве. Обнаруженные реологические характеристики ВЭР позволяют рассматривать данные расплавы как перспективные функциональные материалы: припои, теплоносители электрические контакты

Effect of heat treatment conditions on electrical resistivity of 35KhGF molten steel

The authors have studied the effect of the grain structure, crystal structure and defects of 35KhGF steel samples on the character of temperature dependence of the melt specific electrical resistance at temperatures of 1450–1720 °C. Grain and crystalline structures changed as a result of heat treatment - normalization and tempering. The peculiarities of grain and crystalline structures, the defects were recognized according to the results of metallographic study. The metallographic study was carried out by diffraction of backscattered electrons-EBSD analysis. Scanning areas were chosen with the inclusion of defects in metal of technological origin, namely, microscopic discontinuities filled with gas or slag. The results of EBSD analysis are drawn as IPF-patterns; they show the texture state of the samples using the color assignment method. The microstructure of a 35KhGF steel sample after normalization at 910 °C has the smallest crystallites (of the order of 1 μm) and the largest extent of the grain boundaries. All samples have defects – discontinuities of the order of 1 μm in size. Specific electrical resistance of molten 35KhGF steel samples was measured by the method of rotating magnetic field in heating mode and subsequent cooling. For samples preliminarily normalized at 910 °C, a discrepancy in the temperature dependences of resistivity and an irreversible decrease in the resistivity temperature coefficient were observed in cooling mode of the melt. The discrepancy between the temperature dependences of the electrical resistivity and the irreversible decrease in the temperature coefficient of the resistivity was analyzed on the basis of the microinhomogeneous structure concepts of metallic melts and the pheno menon of metallurgical heredity. According to the notion of the microheterogeneous structure of metallic melts, the melting of a multiphase steel ingot does not immediately produce a homogeneous solution of the alloying elements in the iron at the atomic level, and a chemically microinhomogeneous state is maintained in a certain temperature range. Looking at the branching of the temperature dependences of the electrical resistivity, the transition of the melt into the state of true solution occurs only near the temperature T* = 1640 °C. The value of temperature T* according to the notion of the structural metallurgical heredity phenomenon depends on microstructure, phase composition and crystalline structure of the initial sample. The presence of discontinuities leads to appearance of an excess volume of melt during metal melting, which is partially retained during cooling and crystallization. In this case, the temperature coefficient of the resistivity in cooling mode is close to zero in absolute value, even at ingot cooling rates of the order of 10 °C/s the crystallization conditions change, in particular, the metal’s propensity to amorphization increases. © 2018, National University of Science and Technology MISIS. All rights reserved

VISCOSITY OF MELT Fe12Mn2C

The temperature dependence of the kinematic viscosity of the Fe12Mn2C melt was measured. The results are discussed in the context of studying microheterogeneity and crystallization conditions of the Fe12Mn2C melt within the framework of the theory of absolute reaction rates.Исследование выполнено при финансовой поддержке РФФИ в рамках научного проекта № 19-33-90198