OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Effect of heat treatment on the structure and properties of high-entropy alloy AlCoCrFeNiNb0.25 Zhanna Kovalevskaya а, *, Yuanxun Liu b National Research Tomsk Polytechnic University, 30 Lenin Avenue, Tomsk, 634050, Russian Federation a https://orcid.org/0000-0003-3040-8851, kovalevskaya@tpu.ru; b https://orcid.org/0009-0002-8501-2643, yuansyun1@tpu.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2025 vol. 27 no. 3 pp. 137–150 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2025-27.3-137-150 ART I CLE I NFO Article history: Received: 10 April 2025 Revised: 24 April 2025 Accepted: 13 June 2025 Available online: 15 September 2025 Keywords: High-Entropy Alloy AlCoCrFeNiNb0.25 Heat Treatment Microstructure Microhardness Compression Tests ABSTRACT Introduction. Currently, one of the most studied high-entropy alloys (HEAs) is the CoCrFeNi system with the addition of a fifth component. An example of such an alloy is AlCoCrFeNi alloyed with additional elements. Nb alloying promotes the formation of a solid solution and a secondary Laves phase in the alloy, and leads to the formation of eutectics between these phases. The optimal combination of mechanical properties achieved in the hypoeutectic alloy AlCoCrFeNiNb0.25 was the basis for the choice of this alloy for further studies under heat treatment conditions. Purpose of the work. To investigate the effect of heat treatment, including heating to temperatures of 900°C, 1,000°C and 1,100°C with subsequent cooling in air, on the structure and properties of AlCoCrFeNiNb0.25. The methods of investigation were optical metallography, X-ray diffraction analysis, microhardness measurement, and compression tests. Results and Discussion. AlCoCrFeNiNb0.25 alloy retains the solid solution structure based on the BCC phase not only in the cast state, but also after heat treatment. Irrespective of heat treatment parameters, the alloy retains the hypoeutectic structure consisting of solid solution dendrites and eutectic with the Laves phase in the interdendritic space. Heat treatment leads to changes in the phase composition of the alloy and refinement of structural components. When heated to 900°C, along with the existing solid solution and Laves phase, σ-phase is released in the structure, which increases the microhardness of the alloy, but does not provide improvement of strength properties due to its low plasticity. The strength properties of the alloy are significantly improved by heat treatment with heating up to 1,000°C and 1,100°C. Heating up to 1,100°C is accompanied by an increase in residual strain. The main reasons for this effect may be transformations occurring both in the solid solution of the BCC phase (dissolution of the B2 phase, rearrangement of the substructure, increase in the lattice parameter) and in the eutectic (increase in the proportion of the Laves phase, refinement of eutectic cells). For citation: Kovalevskaya Z.G., Liu Y. Effect of heat treatment on the structure and properties of high-entropy alloy AlCoCrFeNiNb0.25. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2025, vol. 27, no. 3, pp. 137–150. DOI: 10.17212/1994-6309-2025-27.3-137-150. (In Russian). ______ * Corresponding author Kovalevskaya Zhanna G., D.Sc. (Engineering), Professor National Research Tomsk Polytechnic University, 30 Lenin ave., 634050, Tomsk, Russian Federation Tel.: +7 3822 706-351, e-mail: kovalevskaya@tpu.ru Introduction For over two decades, the global community of materials scientists has been developing and investigating a novel class of metal alloys, known as high-entropy alloys (HEAs) [1–4]. Unlike conventional metal alloys with a single principal component, HEAs are composed of multiple principal components in equiatomic or near-equiatomic concentrations [3]. Due to the high mixing entropy, HEAs typically exhibit disordered solid solutions. This phase configuration endows them with enhanced strengthening capabilities and favorable ductility characteristics, making HEAs promising candidates for structural materials [4–6]. One of the most extensively studied systems is the CoCrFeNi alloy, which is often modified by the addition of a fifth element, such as Cu, Mo, Mn, or Al [7–11]. For instance, the thoroughly studied AlCoCrFeNi alloy demonstrates excellent synergy of its constituents, as well as the ability to control its phase composition and structure by heat treatment. Consequently, the resulting alloy achieves an advantageous combination of strength and ductility properties [12–19]. In the search for optimal HEA compositions for the manufacture of machine components, contemporary researchers are advancing in two primary directions: either reducing/increasing the content of one of the
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