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Article

Enhanced Strength–Ductility Synergy of Fine-Grained AlCoCrFeNi High-Entropy Alloy Prepared by Heavy Hot Deformation

by
Sujun Lu
1,†,
Jingou Yin
2,†,
Zhenyu Dou
2,*,
Ming Wei
2,
Jian Wang
2,
Xintao Zhang
1 and
Baoguang Zhang
2
1
State Key Laboratory of Ni&Co Associated Minerals Resources Development and Comprehensive Utilization, Jinchang 737100, China
2
State Key Laboratory of Porous Metal Materials, Northwest Institute for Nonferrous Metal Research, Xi’an 710016, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Materials 2026, 19(4), 708; https://doi.org/10.3390/ma19040708
Submission received: 24 December 2025 / Revised: 20 January 2026 / Accepted: 29 January 2026 / Published: 12 February 2026
(This article belongs to the Special Issue High-Performance Alloys and Steels: Design, Processing, and Applications)
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Abstract

The mechanical properties of the AlCoCrFeNi high-entropy alloy (HEA) can be significantly enhanced by grain refinement. However, it is difficult to refine the grain size of AlCoCrFeNi HEA by solidification methods. In this study, fine-grained AlCoCrFeNi HEA was successfully prepared by heavy thermal mechanical processing. The AlCoCrFeNi HEA consists of FCC, B2, and BCC phases. The FCC phase is distributed on grain boundaries, while the B2 phase is embedded in the BCC matrix within the grains. The fine-grained AlCoCrFeNi HEA has enhanced strength and ductility compared with its coarse-grained counterpart. The enhanced strength–ductility synergy of the fine-grained AlCoCrFeNi HEA is attributed to three key factors: the fine-grained microstructure, the delayed initiation of cracks within the hard-to-deform grain matrix, and the impediment of crack propagation by the grain boundaries enriched with the FCC phase.

Graphical Abstract

1. Introduction

High-entropy alloys (HEAs) exhibit promising properties such as high strength at high temperatures, good oxidation resistance, and outstanding wear resistance together with excellent corrosion resistance [1,2,3,4,5,6]. Among these HEAs, the equimolar AlCoCrFeNi HEA is the subject of extensive studies due to its excellent mechanical properties and relative ease of preparation [7,8,9,10,11].
The AlCoCrFeNi HEA generally consists of disordered BCC, B2 (ordered BCC), and FCC phases. The phase transformation from BCC to FCC occurs under the condition of high-temperature annealing. The improvement in mechanical properties on the AlCoCrFeNi HEA can be significantly adjusted by the fraction of FCC and its distribution in the microstructure [11]. The AlCoCrFeNi HEAs are mainly prepared by conventional casting. Previous studies have been involved in tailoring the microstructure by heat treatments to improve the strength and plasticity of the AlCoCrFeNi HEA [12,13,14]. The mechanical properties of as-cast AlCoCrFeNi HEAs are negatively influenced by casting defects such as dendrite structure, compositional segregation, and large grain sizes [14,15]. The mechanical properties of as-cast HEAs can also be greatly improved by grain refinement, which can be realized by increasing the cooling rate of the solidification [16,17,18]. In order to obtain more rapid solidification, it is necessary to reduce the dimension of the cross section of the AlCoCrFeNi HEA ingot [16]. This strategy limits the application of as-cast AlCoCrFeNi HEA. Additive manufacturing is an alternate way to fabricate fine-grained AlCoCrFeNi HEA [8,19]. The grain size of AlCoCrFeNi HEA using selective laser melting (SLM) can be significantly reduced. However, the reduction in grain size of the AlCoCrFeNi HEA by SLM is still several tens of micrometers [19]. In fact, the equimolar AlCoCrFeNi HEA is difficult to deform due to its phase composition [20]. Further grain refinement can be realized by large deformations on AlCoCrFeNi HEA, such as the thermal powder spraying, which can reduce the grain size to several micrometers [21]. However, such fine-grained structures are limited to the surface layer of the AlCoCrFeNi HEA [22]. Spark plasma sintering (SPS) of AlCoCrFeNi HEA powders can also be used to produce dense bulk alloys with fine-grain structures [20]. However, these mechanical properties are poor due to the existence of prior particle boundaries (PPBs) [23]. The processing of bulk AlCoCrFeNi HEA using a severe plastic deformation technique like hot extrusion has not been extensively explored, particularly regarding its potential to simultaneously eliminate defects and achieve grain refinement. In light of the significant grain refinement of the large deformed AlCoCrFeNi HEA by the thermal powder spraying [24,25], powder extrusion as a heavy deformation method can be applied to prepare the density of hard-to-deform alloys [26,27]. In addition, the harmful PPBs of the alloy powders can be effectively eliminated by large deformation via hot extrusion [23]. In this study, the fine-grained AlCoCrFeNi HEA bulk was obtained via powder hot extrusion. The average grain size of the as-extruded AlCoCrFeNi HEA is about 5 μm, much smaller than those by other methods, such as casting and additive manufacturing [16,17,18,19]. The fine-grained AlCoCrFeNi HEA bulk demonstrates enhanced mechanical properties with the compressive yield strength of about 1460 MPa, ultimate strength of about 3500 MPa, and fracture strain of about 40%.

2. Materials and Methods

The AlCoCrFeNi HEA bulk was prepared by a hot extrusion method on equimolar AlCoCrFeNi HEA powder. The commercial AlCoCrFeNi HEA raw powders (JINCHUAN GROUP Co., Ltd., Jinchang, China) used in this study were fabricated by a gas atomization method. The particle sizes of AlCoCrFeNi HEA ranged from 34 to 178 μm. To prepare the bulk AlCoCrFeNi HEA with fine structure, alloy powders were subjected to hot extrusion. Before the extrusion, the powders were encapsulated into a carbon steel tank with the dimensions of 55 mm in diameter and 150 mm in length, and sealed in a vacuum. The encapsulated powders were pre-heated at 1200 °C for 1 h, and immediately subjected to hot extrusion with an extrusion ratio of 8:1 on a hydraulic press (Schloemann-Siemag 2500 T, Düsseldorf, Germany). The speed of the extrusion was 10 mm/s. The as-extruded bulk was cooled in the air after the hot extrusion. To obtain the original microstructure of the alloy powders right before the hot extrusion after preheating, the alloy powders were sealed in vacuum silicon quartz glass tube, and annealed at 1200 °C for 1 h, followed by water quenching. Phase constitutions were analyzed by an X-ray diffractometer (XRD, Bruker D8, Advance Phaser, Ettlingen, Germany) with Cu Kα radiation. Specimens were polished and etched using aqua regia (HCl:HNO3 = 3:1 volume ratio) to reveal the microstructures. Microstructures were observed by optical microscopy (OM, CX41, Olympus, Tokyo, Japan), scanning electron microscope (SEM, HITACHI, SU6600, Tokyo, Japan), and transmission electron microscopy (TEM, Philips, M12, Amsterdam, The Netherlands). Crystallographic analysis was carried out by electron back-scattered diffraction (EBSD, Oxford, UK). Chemical analyses were performed on an Electron Probe Micro-analyzer (EPMA, JXA-8530 F, Tokyo, Japan). Cylindrical compressive samples with a gauge size of ϕ 8 mm × 12 mm were cut from the extruded bar along the extrusion direction. Uniaxial compressive tests were conducted on the universal testing machine (Instron 5982, Norwood, MA, USA) at a loading strain rate of 1 × 10−3/s at room temperature.

3. Results and Discussion

Figure 1 displays the SEM images of the gas-atomized AlCoCrFeNi HEA powders. The gas-atomized powders have a spherical shape, as shown in Figure 1a. The chemical compositions of the as-atomized powders and as-extruded AlCoCrFeNi HEA are measured and listed in Table 1. The concentration of oxygen is low in both as-atomized powders and as-extruded AlCoCrFeNi HEA, although the increase in oxygen is very small, only from 140 ppm to 330 ppm. Figure 1b gives the cross-section view of the gas-atomized HEA powder particle. A fine structure can be observed in the powder. The fine structure is formed due to the rapid solidification during the gas atomization [21,25]. The elemental segregation occurs on the grain boundaries and interior of the grain. Cr and Fe are enriched on the grain boundary, while Al and Ni are abundant on the matrix [21].
Figure 2 shows the XRD patterns of the atomized, annealed alloy powders and the as-extruded AlCoCrFeNi HEA. The atomized AlCoCrFeNi HEA powders consist of BCC/B2 phases [21,25]. Those BCC/B2 phases can also be found in annealed alloy powders. Additional FCCs along with B2 and BCC phases are detected in the extruded AlCoCrFeNi HEA. It has been reported that no FCC phase can be formed in the atomized AlCoCrFeNi HEA powder with the powder size over 60 μm during a large deformation [21]. However, by further annealing, the formation of the FCC phase occurs in the heavily deformed AlCoCrFeNi HEA powders [21,22].
It is important to study the evolution of the microstructure during the hot extrusion based on the microstructure of the powders immediately prior to the extrusion after preheating. Figure 3 displays the back-scattered electron (BSE) image of the microstructure of the alloy powders annealed at 1200 °C for 1 h. The fine grains of the atomized powders disappear due to recrystallization after the annealing. The annealed alloy powder consisting of the BCC/B2 phase are shown with a red line in the XRD pattern in Figure 2. This phenomenon indicates that the alloy powders have a similar microstructure right before hot extrusion and after preheating.
Figure 4 shows the microstructure of the alloy after the hot extrusion. The morphology of the alloy powders disappeared, suggesting that alloy powders are subjected to a large deformation during the extrusion. The PPBs of alloy powders are effectively eliminated during the hot extrusion [21]. Equiaxed fine grains with an average grain size of about 5 μm can be found both on the parallel direction (PD) and the transverse direction (TD). For bulk AlCoCrFeNi HEA, the grain size of the extruded AlCoCrFeNi HEA is much smaller than those by other fabrication methods such as-cast and additive manufacturing. The grain size of as-cast AlCoCrFeNi is about several hundred micrometers [16,17,18]. The grain size of as-SLMed AlCoCrFeNi HEA can be significantly reduced; however, the reduced grain size of AlCoCrFeNi HEA by SLM is still several tens of micrometers [19].
Figure 5 gives the SEM image of the alloy showing the microstructure in detail. It can be observed that the equiaxed grains of the alloy have thick grain boundaries rich in the FCC phase. The width of the grain boundaries is measured to be 0.5 μm. Within the grain, the dark gray and concave region is the BCC phase, while the light dark region is the B2 phase. As shown in Figure 5b, the compositions are analyzed in different sites of the grain labeled in 1, 2, and 3, respectively. The results are shown in Table 2. It can be found that the grain boundary is enriched with Cr and Fe. The matrix of the grain is enriched with Al and Ni.
Figure 6 shows the BSE image and the corresponding EPMA elemental mappings of the extruded AlCoCrFeNi HEA. Elemental segregation can be found on the grain boundaries and interior of the equiaxed grains. The grain boundaries are enriched with Co, Cr, and Fe, while the grain matrix is enriched Al and Ni. However, no apparent elemental segregation is found in the powders after preheating (Figure 3). This suggests that the elemental segregation is formed after hot extrusion, since the extruded bulk still remained at a high temperature before cooling down. Similar elemental segregation is reported on fine-grained AlCoCrFeNi HEA by SLM. No elemental segregation is found in the as-SLMed AlCoCrFeNi HEA. However, the elemental segregation is observed after annealing at elevated temperatures [19].
Figure 7 exhibits the EBSD results of the as-extruded AlCoCrFeNi HEA. The inverse pole figure (IPF) map reveals that the microstructure of the as-extruded AlCoCrFeNi HEA is composed of fine equiaxed grains. As shown in Figure 7a, the crystallographic orientations are randomly distributed since no dominant colors are apparent in the IPF map. The phase distribution is shown in Figure 7b. Three phases of BCC, B2, and FCC are found in the phase map. The B2 phase is the ordered phase of the BCC. The BCC and B2 phase are the main phases located within the grain matrix. The FCC phase is predominantly distributed on grain boundaries with a fraction of 11.7%. The grain size distribution is shown in Figure 7c. The average grain size of the alloy is about 5 μm. And in Figure 7d, most of the grain boundaries are high-angle grain boundaries (HAGBs > 15°), suggesting that a dynamic recrystallization (DRX) occurs during the hot extrusion [26,28,29,30,31,32]. Incidentally, the fine-grained AlCoCrFeNi HEA can also be produced by additive manufacturing (AM). However, the grain size is several tens of micrometers, which is much larger than that of the present work [19].
Figure 8 shows TEM images and the corresponding SAED patterns of the fine-grained AlCoCrFeNi HEA. Figure 8a shows the image of the triple junction of grain boundaries. In this area, grains are free of dislocations both on grain boundaries and the interior of the grains. SAED analysis confirms that the grain boundaries consist of the FCC phase, while the grain interiors contain both BCC and B2 phases. Within the grains, B2 phase particles are observed embedded in the BCC matrix. Ultra-fine grains (UFGs) with clear grain boundaries can also be found on the grain boundaries. Figure 8b shows the grain boundary with subgrains and a high density of dislocations. The subgrains with dense dislocation walls (DDWs) can be found marked with red arrows. High density of dislocations marked with yellow arrows can also be seen on the FCC grain boundary. However, no dislocations are found within the grain matrix. This indicates that a high density of dislocations formed on the grain boundaries during hot extrusion. The formation of UFGs on the grain boundaries is attributed to the recrystallization.
The schematic diagram of the microstructural evolution during the whole extrusion procedure is described in Figure 9. The original fine-grained atomized powders have the BCC and B2 phase (Figure 1b). After preheating, the phase of the powders is still in the BCC and B2 phase, but the original fine-grained structure becomes a large-grained structure due to the recrystallization (Figure 3). During the hot extrusion, a fine-grained structure formed, and the phase is still in BCC and B2. After extrusion, FCC precipitated on the grain boundaries and thickened before the temperature fell below the FCC transition temperature at about 600 °C [23]. The phase transformation from the atomized AlCoCrFeNi powders to bulk alloy is summarized as follows:
BCC + B2 (As-atomized) → BCC + B2 (Preheating) → BCC + B2 (During extrusion) → FCC + BCC + B2 (After extrusion)
In fact, the FCC phase does not form in the atomized AlCoCrFeNi HEA powders subjected to heavy deformation when the powder size is over 60 μm in diameter [22]. However, the FCC phase is formed in the severely deformed AlCoCrFeNi HEA powder by further annealing [22]. The size of AlCoCrFeNi HEA powders used for the hot extrusion are over 74 μm. In addition, the transformation of the FCC phase does not take place above 1200 °C [22]. It should be noticed that the real deformation temperature of the AlCoCrFeNi HEA is higher than the preheating temperature (1200 °C), because a large amount of latent deformation heat is released during the extrusion process. It is reasonable that no FCC phase is formed during the extrusion. The FCC transformation occurs in a wide temperature range of 600–1200 °C. The as-extruded AlCoCrFeNi HEA rod with 20 mm in diameter has a slow cooling in the air. Before cooling to room temperature, the AlCoCrFeNi HEA bulk will stay in the FCC transition temperature range for a period of time. Thus, the FCC phase formation occurs after hot extrusion.
The mixing enthalpies (−22 kJ/mol) of the Al and Ni elements are lower than those of other elements [19]. The bonding force between the Al and Ni is the largest among those between other elements. The mixing enthalpies of Fe and Cr are −1 kJ/mol, much higher than those of the Al and Ni elements [19]. The BCC phase abundant of Al and Ni can be easily formed after heat treatment. The dislocation density at the grain boundary is high, while the dislocation density inside the grain is low (Figure 8). The high density of the dislocations on the grain boundaries supplies the extra energy for the FCC transformation, which helps the thermal activation conditions of the alloy reach the heating temperature. The FCC phase enriched with Cr and Fe can be formed on the grain boundaries by precipitating from the BCC phases [19].
Figure 10a shows the compressive engineering stress–strain curve of the as-extruded AlCoCrFeNi HEA. The AlCoCrFeNi HEA exhibits excellent ductile strength with a yield strength (YS), ultimate strength (UTS), and fracture strain of 1460 ± 50 MPa, 3500 ± 100 MPa, and 42 ± 3%, respectively. The mechanical property comparisons between the as-extruded AlCoCrFeNi HEA and those prepared by other processing methods are shown in Figure 10b. The mechanical properties of the as-extruded AlCoCrFeNi HEA can be found on the upper right. The AlCoCrFeNi HEA exhibits a good combination of strength and ductility compared with other methods [11,12,13,16,17,18,19,33]. The mechanical properties of as-cast HEAs can be improved by grain refinement [16,17]. Grain refinement in the as-cast AlCoCrFeNi high-entropy alloy (HEA) can be achieved through higher solidification cooling rates. As depicted in Figure 10b, both the strength and ductility of this alloy increase corresponding to the grain size reduction resulting from enhanced cooling during solidification [16,17,18]. The good mechanical property is mainly attributed to the fine-grained microstructures. The grain sizes of the AlCoCrFeNi HEA are much finer than those of its as-cast counterparts [18]. The strength and ductility trade-off properties of the as-extruded AlCoCrFeNi HEA are apparently higher than those of as-cast AlCoCrFeNi HEAs. In addition, due to the finer grains, the strength of the as-extruded AlCoCrFeNi is also higher than that of its as-SLMed counterparts [19].
Figure 11 gives the kernel average misorientation (KAM) maps of the extruded alloy before and after compression. The KAM value is related to the geometrically necessary dislocations (GNDs) [19]. The higher KAM value suggests higher dislocation density in the grains. The different local strain can be observed between the grain boundaries and in the interior of the grains. As observed from the color scales in KAM maps, higher KAM values predominantly highlight some grain boundaries prior to compression (Figure 11a), while lower values are found within the grains. Following deformation (Figure 11b), however, higher KAM values appear along all grain boundaries and increase significantly compared to the pre-deformation state. The color of the yellow green on the grain boundaries before compression becomes bright yellow after the compression. The yellow color of the KAM on the grain gradually changes to blue towards the grain center. This implies that, after the compression, the higher strain is subjected to the grain boundaries and spreads towards the interior of the grain. The deformation is preferentially introduced on the grain boundaries and spreads to the grain matrix.
Figure 12 shows the microstructural evolution of alloy grains before and after compression. Prior to deformation, the grains exhibit straight and smooth grain boundaries, as illustrated in Figure 12a. Following compression (Figure 12b), significant strain is predominantly accommodated within the grain boundaries. This results in the boundaries becoming undulated and rough. In contrast, the morphology of the B2 phase within the grain interiors shows little change before and after compression. This indicates that less strain is transferred to the grain matrix, while a greater portion of the strain is concentrated within the thickened boundary regions. The phenomenon can be attributed to two factors. One is the soft FCC phase at the boundaries. The nanohardness of different phases of AlCoCrFeNi HEA is reported using nanoindentation testing. The nanohardness of FCC (≈3.4 GPa) is much smaller than that of BCC (≈5.5 GPa) and B2 (≈9.1 GPa) [34]. The FCC phase located at the grain boundaries is significantly softer than the BCC and B2 phases constituting the grain matrix. Consequently, strains are more readily introduced and accommodated within these boundary regions. The other is the increased volume fraction of boundaries in fine grains. The fine-grained AlCoCrFeNi HEA possesses a substantially larger volume fraction of thickened grain boundaries rich in the FCC phase compared to its coarse-grained counterpart [15,16,17,18]. This facilitates a more homogeneous distribution of strain throughout the boundary network.
The enhanced strength–ductility synergy of the HEA can be attributed to the delayed crack initiation and prevented crack propagation [35,36]. The fine-grained AlCoCrFeNi high-entropy alloy (HEA) comprises FCC, BCC, and B2 phases. Cracks preferentially initiate within the matrix grains, which are composed of the hard deformable BCC and B2 phases. Conversely, crack initiation is delayed in the matrix of grains with the FCC-enriched grain boundaries. This delay occurs because strain is predominantly accommodated at the FCC-enriched grain boundaries, subjecting the grain interiors to less strain. Consequently, the matrix grains experience reduced strain, leading to a lower density of introduced dislocations. Therefore, a higher strain is required at the crack tip within the matrix grains to accumulate sufficient stress concentration for crack extension, thus increasing the resistance to crack propagation.
Figure 13 presents the TEM microstructure of the alloy bulk after compression, revealing distinct deformation characteristics at different locations. The upper grain boundary region shows a relatively intact shape and contains dislocation tangles, suggesting it has undergone limited strain. In contrast, the vertical grain boundary is heavily distorted and no longer retains its original morphology. A high density of dislocations is observed to be concentrated along this grain boundary. Dislocations are also present within the grain matrix adjacent to this heavily deformed boundary. However, the interior regions of the grain matrix exhibit few dislocations. These observations collectively indicate that predominant strain is accommodated at the FCC-enriched grain boundaries, while significantly less strain is introduced into the grain interiors.
The enhancement in mechanical properties is further attributed to the crack-arresting capability provided by the substantial volume of thick FCC grain boundaries in the fine-grained AlCoCrFeNi HEA. As shown in Figure 14a, when a microcrack encountered a grain boundary, its tip became rounded. This phenomenon indicates the formation of a large-scale plastic zone within the adjacent FCC grain boundaries, thereby releasing the stress concentration at the crack tip. Consequently, the crack tip is blunted, impeding crack extension. Compared to its coarse-grained cast counterpart, this crack-buffering effect is significantly stronger in the fine-grained alloy due to its higher-volume fraction of grain boundaries. Crack buffering is also observed in the fine-grained AlCoCrFeNi HEA fabricated by SLM and subsequent heat treatment, which develops FCC grain boundaries. However, as depicted in Figure 10b, the mechanical properties of the as-SLMed AlCoCrFeNi HEA are inferior to those of the alloy produced in this work. This performance discrepancy can be primarily attributed to the significantly larger grain size in the as-SLMed AlCoCrFeNi HEA, typically on the order of tens of micrometers, which remains substantially coarser than the grain size achieved in our work [19]. Furthermore, the thickened grain boundaries in the present alloy can effectively deflect propagating cracks. As evidenced in Figure 14b, this deflection alters the crack propagation path. The resultant deviation necessitates higher applied loads to further extend the crack, thereby contributing to the observed enhancement in both strength and ductility.
It should be noticed that fine grains can also be achieved in AlCoCrFeNi HEA fabricated via spark plasma sintering (SPS) [33]. However, as shown in Figure 10b, the fine-grained AlCoCrFeNi HEA processed via SPS exhibits inferior mechanical properties compared to the as-extruded alloy developed in this work. The main reason for the performance deficit is primarily attributed to the presence of detrimental PPBs of the SPS material [23]. In contrast, the heavy hot deformation inherent in the extrusion process effectively disrupts these PPBs originating from the powder particles. The elimination of PPBs is a key factor leading to the superior mechanical properties of the as-extruded alloy [23]. Therefore, eliminating PPBs through extrusion processing is crucial for achieving high mechanical performance in AlCoCrFeNi HEAs derived from powders. Fine-grained AlCoCrFeNi HEA can also be obtained by severe plastic deformation such as high-pressure torsion (HPT). The microhardness of the HEA prepared by HPT is outstanding. It increases with reduction in grain size. However, some key parameters such as strength and ductility are missing due to the limited size of the sample by HPT [37]. The equimolar AlCoCrFeNi HEA prepared by hot extrusion demonstrates that substantial thermal deformation via extrusion not only eliminates PPBs effectively but also produces a fine-grained hierarchical structure.

4. Conclusions

In this study, bulk fine-grained AlCoCrFeNi HEA was successfully produced by powder extrusion. The grain refinement is attributed to the dynamic recrystallization (DRX). During the extrusion, the alloy powder is consolidated and subjected to heavy deformation, and the DRX occurred during the extrusion, leading to a grain refinement. The fine-grained AlCoCrFeNi HEA has thick grain boundaries rich in the FCC phase. Within the grain matrix, the B2 phase is embedded in the BCC phase. The fine-grained AlCoCrFeNi HEA has a compressive yield strength of ~1460 MPa, an ultimate strength of ~3500 MPa, and fracture strain of ~40%. A higher volume of grain boundaries rich in the FCC phase as compared with its coarse-grained counterpart is beneficial to the mechanical properties. The crack initiation within the BCC/B2 matrix of the grains is significantly suppressed by the predominant strain imposed on the soft grain boundaries. The good mechanical properties can be attributed to the grain refinement, hindering of crack initiation and crack buffering by the grain boundaries. The complete elimination of PPBs through powder extrusion is the crucial for achieving these good mechanical properties. Further property enhancement of the fine-grained AlCoCrFeNi HEA can be realized by tailoring microstructures through post-processing heat treatments, such as increasing the volume of the FCC phase on the grain boundaries by annealing at proper temperatures. Most significantly, the research establishes a novel processing strategy for developing a high-performance AlCoCrFeNi HEA structural material on an industrial scale with an outstanding strength–ductility synergy.

Author Contributions

J.Y.: Writing—original draft, Writing—review and editing, Methodology, and Formal analysis. S.L.: Writing—original draft, Resources, and Funding acquisition. Z.D.: Writing—review and editing, Formal analysis, Investigation, Resources, and Validation. M.W.: Visualization and Software. J.W.: Investigation, Project administration. X.Z.: Supervision, Visualization. B.Z.: Formal analysis, Methodology. All authors have read and agreed to the published version of the manuscript.

Funding

This study was also supported by the State Key Laboratory of Ni&Co Associated Minerals Resources Development and Comprehensive Utilization (No. GZSYSKY2024081), and the Applied Basic Research Project of the Northwest Institute for Nonferrous Metal Research (No. ZZFY2201).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

Authors Sujun Lu and Xintao Zhang were employed by the company State Key Laboratory of Ni&Co Associated Minerals Resources Development and Comprehensive Utilization. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Materials 19 00708 g001
Figure 1. The secondary electron SEM images of the atomized AlCoCrFeNi HEA powders: (a) morphology, (b) cross-section view.
Figure 1. The secondary electron SEM images of the atomized AlCoCrFeNi HEA powders: (a) morphology, (b) cross-section view.
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Materials 19 00708 g002
Figure 2. XRD pattern of the gas-atomized, annealed powders and as-extruded AlCoCrFeNi HEA.
Figure 2. XRD pattern of the gas-atomized, annealed powders and as-extruded AlCoCrFeNi HEA.
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Materials 19 00708 g003
Figure 3. The secondary electron SEM image of AlCoCrFeNi HEA powders after annealing.
Figure 3. The secondary electron SEM image of AlCoCrFeNi HEA powders after annealing.
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Materials 19 00708 g004
Figure 4. The optical microscopy (OM) images of the as-extruded AlCoCrFeNi HEA from different perspectives, (a) the transverse direction (TD) and (b) the parallel direction (PD).
Figure 4. The optical microscopy (OM) images of the as-extruded AlCoCrFeNi HEA from different perspectives, (a) the transverse direction (TD) and (b) the parallel direction (PD).
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Materials 19 00708 g005
Figure 5. The secondary electron SEM images illustrating (a) the microstructure of as-extruded AlCoCrFeNi HEA and (b) magnified view of (a) with phase composition analysis using the EPMA.
Figure 5. The secondary electron SEM images illustrating (a) the microstructure of as-extruded AlCoCrFeNi HEA and (b) magnified view of (a) with phase composition analysis using the EPMA.
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Materials 19 00708 g006
Figure 6. BSE image and the corresponding EPMA elemental mappings of the extruded AlCoCrFeNi HEA.
Figure 6. BSE image and the corresponding EPMA elemental mappings of the extruded AlCoCrFeNi HEA.
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Materials 19 00708 g007
Figure 7. EBSD results of the as-extruded AlCoCrFeNi HEA: (a) The inverse pole figure map (IPF); (b) phase distribution map; (c) the histograms of the grain size; (d) the histograms of grain boundary misorientation angle.
Figure 7. EBSD results of the as-extruded AlCoCrFeNi HEA: (a) The inverse pole figure map (IPF); (b) phase distribution map; (c) the histograms of the grain size; (d) the histograms of grain boundary misorientation angle.
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Materials 19 00708 g008
Figure 8. TEM images and the corresponding SAED patterns of the as-extruded AlCoCrFeNi HEA: (a) free of dislocations and (b) with dislocations.
Figure 8. TEM images and the corresponding SAED patterns of the as-extruded AlCoCrFeNi HEA: (a) free of dislocations and (b) with dislocations.
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Materials 19 00708 g009
Figure 9. The schematic diagram of microstructure evolution from the gas-atomized powder to hot-extruded bulk.
Figure 9. The schematic diagram of microstructure evolution from the gas-atomized powder to hot-extruded bulk.
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Materials 19 00708 g010
Figure 10. (a) The compressive engineering stress–strain curve; (b) compressive strength versus fracture strain of the extruded AlCoCrFeNi HEA compared with other high-performance materials [11,12,16,18,19,33].
Figure 10. (a) The compressive engineering stress–strain curve; (b) compressive strength versus fracture strain of the extruded AlCoCrFeNi HEA compared with other high-performance materials [11,12,16,18,19,33].
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Materials 19 00708 g011
Figure 11. The KAM maps of the AlCoCrFeNi HEA before and after compression: (a) before compression, (b) after compression.
Figure 11. The KAM maps of the AlCoCrFeNi HEA before and after compression: (a) before compression, (b) after compression.
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Materials 19 00708 g012
Figure 12. The microstructure of AlCoCrFeNi HEA before (a) and after (b) compression.
Figure 12. The microstructure of AlCoCrFeNi HEA before (a) and after (b) compression.
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Materials 19 00708 g013
Figure 13. The TEM images and the corresponding SAED patterns of the AlCoCrFeNi HEA after compression.
Figure 13. The TEM images and the corresponding SAED patterns of the AlCoCrFeNi HEA after compression.
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Materials 19 00708 g014
Figure 14. The microstructure of the AlCoCrFeNi HEA after the compression: (a) crack buffering and (b) crack deflecting.
Figure 14. The microstructure of the AlCoCrFeNi HEA after the compression: (a) crack buffering and (b) crack deflecting.
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Table 1. Chemical composition of the as-atomized powders and the as-extruded AlCoCrFeNi HEA.
Table 1. Chemical composition of the as-atomized powders and the as-extruded AlCoCrFeNi HEA.
ElementsAl at%Co at%Cr at%Fe at%Ni at%O ppm
As-atomized20.0520.0319.8920.1219.91140
As-extruded20.0819.9720.1319.8719.95330
Table 2. Chemical composition of the extruded AlCoCrFeNi HEA. Sites 1, 2, and 3 are associated with the marks in Figure 5b.
Table 2. Chemical composition of the extruded AlCoCrFeNi HEA. Sites 1, 2, and 3 are associated with the marks in Figure 5b.
ElementsAl at%Co at%Cr at%Fe at%Ni at%
Site 114.821.820.724.817.9
Site 227.718.215.118.220.8
Site 326.318.616.218.920.0
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MDPI and ACS Style

Lu, S.; Yin, J.; Dou, Z.; Wei, M.; Wang, J.; Zhang, X.; Zhang, B. Enhanced Strength–Ductility Synergy of Fine-Grained AlCoCrFeNi High-Entropy Alloy Prepared by Heavy Hot Deformation. Materials 2026, 19, 708. https://doi.org/10.3390/ma19040708

AMA Style

Lu S, Yin J, Dou Z, Wei M, Wang J, Zhang X, Zhang B. Enhanced Strength–Ductility Synergy of Fine-Grained AlCoCrFeNi High-Entropy Alloy Prepared by Heavy Hot Deformation. Materials. 2026; 19(4):708. https://doi.org/10.3390/ma19040708

Chicago/Turabian Style

Lu, Sujun, Jingou Yin, Zhenyu Dou, Ming Wei, Jian Wang, Xintao Zhang, and Baoguang Zhang. 2026. "Enhanced Strength–Ductility Synergy of Fine-Grained AlCoCrFeNi High-Entropy Alloy Prepared by Heavy Hot Deformation" Materials 19, no. 4: 708. https://doi.org/10.3390/ma19040708

APA Style

Lu, S., Yin, J., Dou, Z., Wei, M., Wang, J., Zhang, X., & Zhang, B. (2026). Enhanced Strength–Ductility Synergy of Fine-Grained AlCoCrFeNi High-Entropy Alloy Prepared by Heavy Hot Deformation. Materials, 19(4), 708. https://doi.org/10.3390/ma19040708

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