DOI: 10.18503/1995-2732-2026-24-2-82-92
Abstract
Problem Statement (Relevance). The CoCrFeNi high-entropy alloy (HEA) is a low-stacking-fault-energy material, which facilitates twin formation during plastic deformation at cryogenic temperatures. Its equiatomic composition and simple single-phase face-centered cubic (FCC) structure make this alloy one of the most promising candidates for industrial applications. However, in the as-cast condition, the CoCrFeNi HEA exhibits relatively low yield strength (≈200 MPa) and ultimate tensile strength (≈500 MPa). Conventional plastic deformation techniques cannot fully exploit the strengthening potential of the CoCrFeNi HEA; therefore, its mechanical and service properties require further improvement. One promising approach to enhancing the mechanical properties of the CoCrFeNi HEA is asymmetric cryogenic rolling. Cryogenic deformation can promote the formation of nanotwins, while velocity asymmetry between the rolls can facilitate the formation of shear bands with a high dislocation density and induce a transition in the deformation mechanism from dislocation slip to deformation twinning. Therefore, investigating the deformation and strengthening mechanisms operating in the CoCrFeNi HEA during asymmetric cryogenic rolling is of significant scientific and practical interest. Objectives. The research is aimed at investigation of the effect of asymmetric cryogenic rolling on the microstructure and mechanical properties of the CoCrFeNi high-entropy alloy. Methods Applied. The CoCrFeNi HEA was produced at the Central South University (Changsha, China) using vacuum levitation melting. The microstructure and mechanical properties of the alloy were studied both in the as-cast state and after three different rolling conditions: (1) symmetric rolling at room temperature (25°C); (2) symmetric cryogenic rolling (-196°C); and (3) asymmetric cryogenic rolling (-196 °C). The asymmetric cryogenic rolling experiments were also carried out at Central South University (Changsha, China) using a four-high reversing mill with work rolls of equal diameter (80 mm) and a specified roll speed ratio . Liquid nitrogen was used to create cryogenic rolling conditions. Initial sheet specimens with dimensions of 3×50×150 mm were rolled in several passes to final thicknesses of 2.4, 1.8, 1.2, and 0.6 mm. Tensile tests were performed using a Shimadzu AGS-X 10 kN universal testing machine. The homogeneity of elemental distribution was evaluated by energy-dispersive spectroscopy (EDS) using an Oxford X-Max20 unit. Electron backscatter diffraction (EBSD) analysis was carried out using a Nordlys Max3 detector attached to a JSM-7800F field-emission scanning electron microscope. EBSD data were processed using Aztec Crystal software. The microstructure of samples subjected to a total reduction of 80% was additionally examined using a Philips CM200 field-emission gun transmission electron microscope (FEG-TEM). Results. The CoCrFeNi HEA subjected to asymmetric cryogenic rolling with a total thickness reduction of 80% achieved the highest strength among the three rolling conditions, reaching 1.45 GPa. It was established that this superior strength resulted from the formation of nanotwins generated by the accumulation of stacking faults during asymmetric cryogenic rolling. Practical Relevance. The results of this study can be used to optimize plastic deformation regimes for the CoCrFeNi high-entropy alloy and improve its mechanical performance for applications under extreme service conditions.
Keywords
CoCrFeNi high-entropy alloy, asymmetric cryogenic rolling, roll speed asymmetry, deformation, microstructure, mechanical properties.
For citation
Wu Y., Yu H., Pesin A.M., Pustovoytov D.O. Influence of Asymmetric Cryogenic Rolling on the Microstructure and Mechanical Properties of a CoCrFeNi High-Entropy Alloy. Vestnik Magnitogorskogo Gosudarstvennogo Tekhnicheskogo Universiteta im. G.I. Nosova [Vestnik of Nosov Magnitogorsk State Technical University]. 2026, vol. 24, no. 2, pp. 82-92. https://doi.org/10.18503/1995-2732-2026-24-2-82-92
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