The Structural and Thermodynamic Analysis of Phase Formation Processes in Equiatomic AlCoCuFeNiCr High-Entropy Alloys
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JMEPEG https://doi.org/10.1007/s11665-020-05250-6
The Structural and Thermodynamic Analysis of Phase Formation Processes in Equiatomic AlCoCuFeNiCr High-Entropy Alloys M. Dufanets, V. Sklyarchuk, Yu. Plevachuk
, Y. Kulyk, and S. Mudry
Submitted: 9 May 2020 / Revised: 29 September 2020 / Accepted: 9 October 2020 Phase formation processes in equiatomic AlCoCuFeNiCr high-entropy alloys have been studied by means of x-ray diffraction method, microstructure analysis and microhardness measurements. Thermodynamic and structural criteria for predicting the phase composition of the alloys were considered. It is shown that in AlCoCuFe, AlCoCuFeNi and AlCoCuFeNiCr alloys the two-phase mixture of solid solutions on the base of the BCC and FCC lattices is formed. With a decrease in the fraction of Al atoms, the tendency to disordering of BCC solid solution occurs. It was also established that alloys under investigation reveal a dendritic structure in which Cu-enriched FCC phase is deposited in the regions between the dendrites of the main BCC phase. The correlation between microhardness of the alloys and volume fractions of phase constituents and their thermodynamic characteristics are revealed. Keywords
enthalpy of mixing, high-entropy alloys, phase transformation, solid solution, structure, x-ray analysis
1. Introduction Recently, the significant fundamental and applied interest began to be shown in multicomponent alloys, in which content of each constituent element is equal. The entropy of such alloys increases with increasing number of elements and is close to ideal entropy of a multicomponent solution. Due to a high value of the entropy of mixing, there is a possibility to high thermodynamic stability of disordered atomic solutions (Ref 13). Experimental studies showed evidently that high-entropy alloys (HEAs) have unique physicochemical and mechanical properties, such as high hardness, wear resistance, thermal stability and corrosive resistance. Such alloys can combine strength (Ref 4), stability to softening (Ref 5) and plasticity (Ref 6) that allows to use them as tools in machine building industry and metallurgy. However, it should be noted that in many HEAs the formation of solid solutions occurs (Ref 2, 7) and their deposition during solidification is the main reason of degradation of the mechanical properties. It is obvious that high entropy of mixing is not only one and sufficient criterion for HEA formation condition. For this reason, it is important to find and apply another criterion for controlled processes of the formation of alloys with desired structure. The results of experimental studies allowed to conclude that phase formation during HEA solidification depends significantly on difference of atomic radii of constituent elements, their electron concentration and thermodynamic parameters. But it should be noted M. Dufanets, V. Sklyarchuk, Yu. Plevachuk, Y. Kulyk, and S. Mudry, Department of Metal Physics, Ivan Franko National University of Lviv, Kyrylo & Mephodiy Str. 8, Lviv 79005, Ukraine. Contact e-mail: p
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