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Journal of Physical Studies 25(3), Article 3601 [7 pages] (2021)
DOI: https://doi.org/10.30970/jps.25.3601 ELECTRICAL CONDUCTIVITY AND THERMOPOWER OF HIGH-ENTROPY AlCoCrCuFeNi LIQUID ALLOYS
M. Dufanets, Yu. Plevachuk
Ivan Franko National University of Lviv
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Conventional alloys are mainly based on one principal element with different kinds of alloying elements added to improve their properties. These alloys form an alloy family based on the chosen principal element. However, the number of elements in the periodic table is limited, thus the alloy families which can be developed are also limited. The new concept has been named a high-entropy alloy (HEAs). According to the proposed definition, any multi-component alloy consisting of five or more principal elements which have a concentration between 5 and 35 at.%, belongs to HEA. Besides principal elements, HEAs could contain also minor elements with concentrations below 5 at.%. Compared to conventional alloys, these alloys have significantly higher mixing entropies, which lead to the formation of liquid or random solid solution states. Thus, the effect of entropy is much more pronounced in high-entropy alloys than in conventional alloys. The high entropy of mixing in these alloys facilitates the formation of solid solution phases with simple structures. Thus, it reduces the number of phases formed in HEAs during solidification process. Such unique structural features caused by the effect of higher entropy are of paramount importance for further industrial application of these alloys.
Due to the unique multi-principal element composition, the high-entropy alloys can have extraordinary properties, including high strength/hardness, outstanding wear resistance, exceptional high-temperature strength, good structural stability, good corrosion and oxidation resistance. Some of these properties are not seen in conventional alloys, making HEAs attractive in many fields. The fact that they can be used at high temperatures broadens their spectrum of applications even further. Moreover, the fabrication of HEAs does not require special processing techniques or equipment, which indicates that the mass production of HEAs can be easily implemented with existing equipment and technologies. The development of new advanced materials with predicted properties requires a clear and thorough understanding of their structural properties on the basis of sufficient and reliable thermophysical data. The increasing influence of computational modeling in all technological processes generates an increased demand for accurate values of the physical properties of the materials involved, which are used as fundamental inputs for each model. The solidification process of a liquid alloy has a profound impact on the structure and properties of the solid material. Therefore, knowledge of the thermophysical properties of molten alloys becomes very important for understanding the structural transformations in alloys in the liquid-solid temperature range and modeling the solidification process, so that materials with required characteristics can be developed.
In this study, experimental measurements of electrical conductivity and thermoelectric power of the liquid HEAs of equiatomic concentrations Al$_{16.6}$Co$_{16.6}$Cr$_{16.6}$Cu$_{16.6}$Fe$_{16.6}$Ni$_{16.6}$, Al$_{20}$Co$_{20}$Cu$_{20}$Fe$_{20}$Ni$_{20}$, Al$_{25}$Co$_{25}$Cu$_{25}$Fe$_{25}$, Al$_{25}$Co$_{25}$Cr$_{25}$Ni$_{25}$ and Co$_{20}$Cr$_{20}$Cu$_{20}$Fе$_{20}$Ni$_{20}$ were carried out in a wide temperature range from their melting points to 1750 K.
Key words: high-entropy alloys, electrical conductivity, thermoelectric power
