Viscosity and electrical resistivity of liquid cunial, cunialco, cunialcofe alloys of equiatomic compositions

The kinematic viscosity and electrical resistivity of equiatomic liquid alloys CuNiAl, CuNiAlCo, CuNiAlCoFe has measured during heating of the sample to 2070 K and subsequent cooling. We consider CuNiAl, CuNiAlCo, CuNiAlCoFe alloys of equiatomic compositions as the multi-principal element alloys (MPEAs), the complex concentrated alloys (CCAs), the high-entropy alloys (HEAs). The measuring results of the vickosity and the resistivity are discussed on base the available microgeterogenity concept. We searched the temperatureT*of the heating a melt for destroy of microheterogeneity. T* is the temperature of the beginning of the matching portion of the temperature dependence of the viscosity and resistivity which is obtained by heating and cooling. All the investigated melts demonstrated different temperature dependence of viscosity for heating and cooling. The temperature T*=1800 K were determined only for liquid alloy CuNiAl of equiatomic composition. For alloys CuNiAlCo, CuNiAlCoFe the coinciding part of the temperature dependences of the viscosity which are obtained by heating and cooling is absent. The results of viscosity are discussed within the theory of absolute reaction rates. Entropy of activation of viscous flow and free activation energy of viscous flow were determined by analyzing the temperature dependences of kinematic viscosity. The increasing of components quantity in the alloy leads to the increasing of the free activation energy of viscous flow and the volume per structural unit of the melt (ion, atom, or cluster). The measuring results of resistivity were interpreted using the Nagel-Tauc model. The temperature coefficient of resistivity (characteristic of the structural state of the melt) was determined. The temperature dependences of the CuNiAl liquid alloy resistivity measured upon heating to 2070 K and subsequent cooling do not coincide.The value of T*temperature for alloy CuNiAl of equiatomic composition is 1850 K. For CuNiAlCo, CuNiAlCoFe alloys the temperature dependences of the resistivity which are obtained by heating and cooling are coinciding. This means that destroy of microheterogeneity for melts after heating up to 2070K did not occur. The temperature coefficient of resistivity of the CuNiA liquid alloy irreversibly decreases when it heated to a temperature of 1850 K.This is evidence of the destruction of microheterogeneity with the formation of a homogeneous solution at the atomic level. The increasing of components quantityin the alloy leads to a decreasingof thetemperature coefficient of the resistivity (in cooling moda). According to the ideas of Nagel and Tauk, an irreversible decrease of the temperature coefficient of the specific resistance of the melt indicates an increase in the volume per structural unit of the melt (ion, atom, or cluster). © 2019, Technical University of Kosice. All rights reserved.Authors are grateful for the support of experimental works by Act 211 Government Russian Federation, contract 02.A03.21.0006

Surface Tension and Density of Fe–Mn Melts

Abstract: The article presents original experimental data on surface tension of the Fe100 – xMnx (x = 4–13 wt %) melts. Surface tension and density of the melt were measured by the sessile drop method at heating from the liquidus temperature to 1780°C and subsequent sample cooling in the atmosphere of high-purity helium. Temperature and concentration dependences of surface tension and density of Fe–Mn melts were plotted. Manganese is a surface-active substance in iron melt. The value of surface tension coefficient of Fe–Mn melts decreases as Mn content increases. Experimental data on the surface tension of Fe–Mn melts is consistent with the theoretical dependences (the Pavlov–Popel’ equation and the Shishkovsky equation). During the investigation of Fe–Mn melt microheterogenity, correlation between the values of kinematic viscosity, surface tension, and density is revealed. Fluidity dependence of Fe–Mn melts on their density in the cooling mode has a linear character which indicates satisfaction of the Bachinskii law. Discrepancy in the melt viscosity ratios to the surface tension coefficient obtained from the experimental data and from the empirical formula is discovered. Using the experimental data on viscosity and surface tension of Fe–Mn melts, the entropy change in the melt’s bulk and the change in the melt’s surface entropy, respectively, are studied. The surface entropy and the bulk entropy in the melt decrease in their absolute value with its increasing Mn content. From the study results, it is concluded that there is no destruction of the microheterogeneous structure of Fe100 – xMnx (x = 4–13 wt %) melts when heated up to 1780°C. © 2020, Allerton Press, Inc.The reported study was funded by Russian Foundation for Basic Research, project no. 19-33-90198

Electrical resistivity of liquid CuSn, CuSnBi, CuSnBiIn, CuSnBiInCd alloys of equiatomic compositions

The resistivity of liquid CuSn,CuSnBi, CuSnBiIn, CuSnBiInCd alloys of equiatomic compositions are measured using the rotating magnetic field method to obtain information on their liquid structures. The alloys of equiatomic composition we considered as the high-entropy alloys. The results are discussed in the frame of a microheterogeneous structure of a metallic melt. A conclusion is made about the character of the modification of temperature dependence of the resistivity of liquid alloy due this microheterogeneous structure. All the investigated alloys demonstrated the change in the temperature coefficient of the resistivity for heating and cooling. These changes determined the temperature of destruction the microheterogeneous structure of a metallic melt (T∗). The value of temperature T∗ for all alloys was 1070 K (800 °C). The change in the temperature coefficient of the resistivity of the alloys on heating to 1070 K (800 °C) is interpreted using the Nagel-Tauc model. © 2019 Author(s)

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