To achieve a homogeneous distribution of elements in the alloys, each alloy was re-melted four times, flipped before each melting run, and kept in a molten state for 5 min during each run. This resulted in a button-shaped product shown in Figure The second stage in the experimental procedure was the thermal treatments. The cast buttons were cut and annealed at various temperatures, before being quenched in water.
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The following procedures were conducted in each temperature. An accelerating voltage of 20 kV was used; the working distance was 10 mm. The images analyzed by this method were obtained by SEM. In high-entropy alloys based on Zr and BCC elements, such as Cr, Ti, and Nb the first two falling under the wider definition of refractory elements and Nb being a refractory element , a unique phenomenon of gradual Zr segregation as the temperature rises can be observed.
It is more than likely that this phenomenon is not in equilibrium since Zr is expected to have a BCC structure at high temperatures as well. Some Ti is also incorporated in the secluded Zr solid solution regions and, to a small degree, it behaves in the same manner, being an HCP element itself. The other elements are then incorporated in the increasingly Zr-depleted BCC solid solution phase, which gradually grows in volume as the temperature rises further. The Nb-Ti-Zr based solid solution phase appearing at low to moderate temperatures in both alloys forms as a result of the relatively rapid cooling associated with arc melting and is not likely to be the equilibrium solid solution phase predicted at those temperatures by the model.
Eyal Eshed performed the literature survey, established the phase formation sequence based on the obtained results, participated in discussions of the results and the formulation of the conclusions, and wrote the manuscript. Alexey Kovalevsky performed alloy preparations and participated in discussions of the results. Vladimir Popov Jr. Igor Gorbachev performed the thermodynamic modelling of the phase formation in the examined system of materials. Vladimir Popov established the objectives of the thermodynamic modelling and participated in the discussions of its results and in comparison of the modelling results with the experimental obtained ones.
Alexander Katz-Demyanetz established the research objectives, contributed to the literature survey, performed XRD examination of the samples, gathered the results, and participated in discussions of the results and formulation of the conclusions. National Center for Biotechnology Information , U. Journal List Materials Basel v.
Materials Basel. Published online Jan Find articles by Eyal Eshed. Find articles by Natalya Larianovsky.
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Find articles by Vladimir Popov. Find articles by Alexander Katz-Demyanetz. Author information Article notes Copyright and License information Disclaimer. Received Dec 27; Accepted Jan This article has been cited by other articles in PMC.
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Abstract Refractory-based high entropy alloys HEAs of the 2nd-generation type are new intensively-studied materials with a high potential for structural high-temperature applications. Keywords: high-entropy, refractory, thermodynamics, solid solution, intermetallic phase. Introduction High entropy alloys HEAs are, in relative terms, newcomers to the world of metallurgy.
Results 2. Cr 20 Nb 20 Ti 20 V 20 Zr 20 Alloy The following figures Figure 1 a—d show the microstructure of the alloy at designated temperatures i. Open in a separate window. Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Discussion The phase identification performed at each examined temperature for both alloys, based on the EDS measurements, is supported and reinforced by the qualitative XRD analysis.
Figure 9. Figure Table 1 Model prediction of chemical composition of every phase in equilibrium at the designated temperatures. Conclusions In high-entropy alloys based on Zr and BCC elements, such as Cr, Ti, and Nb the first two falling under the wider definition of refractory elements and Nb being a refractory element , a unique phenomenon of gradual Zr segregation as the temperature rises can be observed. Author Contributions Eyal Eshed performed the literature survey, established the phase formation sequence based on the obtained results, participated in discussions of the results and the formulation of the conclusions, and wrote the manuscript.
Conflicts of Interest The authors declare no conflict of interest. References 1. Yeh J. Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes.
Wang Y. Solid solution or intermetallics in a high-entropy alloy.
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Zhang Y. Alloy design and properties optimization of high-entropy alloys. Senkov O.
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Alloys Compd. Microstructure of Aluminum-containing refractory high-entropy alloys. Microstructure and mechanical properties of Al x Si 0. Klimova M. Liu X. Feng W. Popov V.
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