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Article

Microstructure, Mechanical Properties, and Damping Capacity of AlxCoCrFeNi High-Entropy Alloys Prepared by Spark Plasma Sintering

by
Ke Xiong
1,2,
Lin Huang
1,2,*,
Xiaofeng Wang
1,2,
Lin Yu
1,3 and
Wei Feng
1,2,*
1
School of Mechanical Engineering, Chengdu University, Chengdu 610106, China
2
Sichuan Province Engineering Technology Research Center of Powder Metallurgy, Chengdu 610106, China
3
Sichuan Yiran Material Technology Co., Ltd., Chengdu 610100, China
*
Authors to whom correspondence should be addressed.
Metals 2022, 12(12), 2058; https://doi.org/10.3390/met12122058
Submission received: 12 November 2022 / Revised: 23 November 2022 / Accepted: 28 November 2022 / Published: 29 November 2022
Browse Figures
Versions Notes

Abstract

:
High-entropy alloys (HEAs) of AlxCoCrFeNi (x = 0.2, 0.5, and 1) were created using the spark plasma sintering (SPS) method in conjunction with an aerosolized powder. Their microstructure and phase constituents were characterized by X-ray diffractometry, scanning electron microscopy, and projection electron microscopy. The tensile properties, hardness, compactness, and damping properties were also tested. The results showed that the crystal structure of AlxCoCrFeNi HEAs changed significantly with the Al content, from the original single face-centered cubic FCC phase (Al0.2CoCrFeNi) to an FCC + BCC + B2 structure (Al0.5CoCrFeNi), and then to FCC + BCC + B2 + Sigma (σ) phase structures (AlCoCrFeNi). Twin crystals with FCC structure were also observed in the TEM of AlCoCrFeNi. A chemical composition analysis showed that the crystal structure transformation was related to the segregation caused by the increase of Al element content. The hardness of the AlxCoCrFeNi HEAs increased with the Al content, and the hardness of AlCoCrFeNi reached the highest value of 585.4 HV. The tensile properties of the alloy showed a trend of increasing and then decreasing values with the increase in Al content. The yield strength, ultimate tensile strength, and elongation of the Al0.5CoCrFeNi alloy reached the highest values of 557.7 MPa, 954.4 MPa, and 32.2%, respectively. Moreover, the fracture mechanism of the Al0.2CoCrFeNi and Al0.5CoCrFeNi alloys was that of a typical ductile fracture, while for the AlCoCrFeNi alloy, it was that of a cleavage fracture. The compactness of the alloy increased with the Al content. The combination of the FCC + BCC + B2 phase resulted in the damping capacity of Al0.5CoCrFeNi alloy reaching 0.018 at the corresponding strain amplitude of 6 × 10−4.

1. Introduction

Traditional alloys are based on the combination of one metal with another one or more metals or non-metal elements to improve their properties [1,2,3]. However, when various elements are combined, different compounds are usually formed, including intermetallic phases with poor mechanical properties, so that the comprehensive properties of the final material do not meet the performance requirements [4,5]. High-entropy alloys (HEAs) are multi-component mixtures of at least five significant elements in equal concentrations. Their unique compositions exert four core effects: high entropy, slow diffusion, lattice distortion, and cocktail effect [6]. The high entropy effect is conducive to forming a stable solid solution phase with a simple structure (body-centered cubic BCC phase, face-centered cubic FCC phase, or mixed phase). It suppresses the formation of many intermetallic phases, thereby avoiding the shortcomings of traditional multiphase alloys [7,8,9].
AlxCoCrFeNi HEAs are reported to be one of the most widely studied high-entropy alloys, with excellent physical and mechanical properties, and are considered a potentially essential engineering material [10,11,12,13,14,15,16,17,18]. At present, AlCoCrFeNi HEA is usually prepared by arc melting or casting [19]. Nevertheless, during the crystallization of the alloy, component segregation will cause a degradation of the mechanical characteristics [20,21]. High-entropy alloys produced using the vacuum arc melt technique necessitate a large amount of energy and money, have an uneven phase composition, or allow for limited product shapes and sizes [22,23]. AlCoCrFeNi HEAs, made in recent years by using powder metallurgy (PM) technologies, which include spark plasma sintering, show a more homogeneous composition, higher density, and smaller grain sizes. Their qualities are outstanding, allowing the decrease or elimination of the metalworking and removal processes, which decreases the damage to AlCoCrFeNi HEAs [24,25,26,27,28,29,30].
Mechanical alloying (MA) is used to create an AlCoCrFeNi HEA powder in the PM process. However, the ball milling duration is high (up to 30 h or more), and the process is contaminated by the grinding medium and process control agents (PCA) used for grinding. The extra order of metal components will also have an effect on the creation of the HEA phase [31,32,33]. AlCoCrFeNi HEA powders with better purity and a more consistent alloying element composition are currently generated via gas atomization [34,35].
The Al element, which promotes the development of the BCC phase, has a significant influence on the microstructure and properties of AlxCoCrFeNi HEAs [36]. By changing the atomic fraction of Al in a typical HEA system, Alx-CoCrFeNi may achieve a single-phase or multi-phase structure [37]. Gangireddy et al. [5,37,38,39] found that the structure of AlxCoCrFeNi HEA changed with the Al content. The alloy transformed from a single-face-centered cubic FCC (x ≤ 0.3) to a (BCC)/B2 + FCC (0.3 < x ≤ 0.6), and eventually, a single-phase BCC structure (x > 0.6), and the increase in Al content led to a significant increase in the BCC + B2 phase fraction; the production of the BCC and B2 phase was the main factor increasing the alloy’s hardness from 120 HV to 500 HV. Liu et al. [40] found that raising the Al concentration in an AlxCoCrFeNi alloy would produce a higher hardness and a lower element diffusion rate, resulting in an excellent oxidation resistance.
There are few reports on the systematic tensile fracture morphology of AlxCoCrFeNi HEAs [12,27,41], as well as on the damping properties of AlxCoCrFeNi HEAs prepared by SPS sintering. However, there have been reports on the damping properties of AlxCrFeNi entropy alloys with better mechanical properties, indicating that these alloys can be used as potential damping materials with practical engineering application value [42]. Therefore, this paper systematically studied AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEAs prepared by SPS, including their microstructure, mechanical properties, and damping properties, providing a basis for future research and engineering applications of the AlxCoCrFeNi HEA system.

2. Materials and Methods

2.1. AlxCoCrFeNi High-Entropy Alloy Prepared by SPS

The AlxCoCrFeNi HEA powder (Jiangsu Vilory Advanced Materials Technology Co. Ltd., Jiangsu, China) utilized in this experiment was made from Al, Co, Cr, Fe, and Ni pure metallic particles, with alloy element purity higher than 99.99 wt%, by the gas atomization method. The AlxCoCrFeNi (x = 0.2, 0.5, and 1) HEA gas-atomized powder was consolidated using a LA-BOX-350 spark plasma-sintering machine (SPS, SINTER LAND INC., Chiyo, Japan), then heated to 1050 °C at a specific heating rate (below 600 °C, the heating rate was 100 °C/min; at 600 to 900 °C, the heating rate was 50 °C/min; above 900 °C, the heating rate was 25 °/min), and finally held at 1050°C for 10 m. During the sintering process, graphite molds with a diameter of 40 mm and a sintering pressure of 20 MPa were used. The sintered samples were denoted Al0.2CoCrFeNi (Al0.2), Al0.5CoCrFeNi (Al0.5), and AlCoCrFeNi (Al1), respectively.

2.2. Microstructural and Mechanical Property Characterization

A DK7735 CNC wire-cutting machine was used to create tensile and damping specimens (Taizhou Weihai CNC Machine Tool Co., Ltd., Taizhou, China). The sintered samples were ground, polished as required, and then tested by different equipment. The crystal structure of the powders and alloys was analyzed with a DX-2700 X-ray diffractometer (XRD, Dandong Haoyuan Instrument Co., Ltd., Dandong, China), and an X-ray tube with copper anode/copper radiation. Moreover, 20–90° 2θ, sampling period of 0.5 s. The FEI-Inspect F50 field emission scanning electron microscope (SEM, FEI Company, Hillsboro, OR, USA) equipped with energy dispersive spectroscopy (EDS) was used to examine the microstructure and composition distribution. The as-sintered samples were additionally characterized by the FEI-Tecnai G2 F20 transmission electron microscope (TEM, FEI Company, Hillsboro, OR, USA) and high-resolution transmission electron microscopy (HRTEM) equipped with chosen-area electron diffraction to further examine the phase component (SAED). Mechanical grinding was used to create 3 mm diameter TEM samples, which were further thinned with an ion shear equipment machine for testing (Shenzhen Wance Test Equipment Co., Ltd., Shenzhen, China). The tensile specimen’s initial gauge length was 5 mm, the cross-sectional area was 1.5 × 1 mm, and the tensile rate was 0.2 mm/min. To avoid mistakes, seven samples of each alloy were evaluated. The MHVD-50AP Vickers hardness tester (Shanghai Jujing Precision Instrument Co., Ltd., Shanghai, China) was used to measure the hardness of the samples; the fixed load was 5 kg, the holding period was 15 s, and an average value of 7 points was recorded for each sample. The density of alloys was measured using the Archimedes method, and the compactness of alloys was determined as the density ratio to theoretical density. To avoid mistakes, each alloy was tested five times.
The Internal Friction Q−1 (Q−1 = tanδ) was used to evaluate the damping capacity of samples with dimensions of 10 mm (w) × 35 mm (l) × 1mm (t) tested at room temperature by the TA Q800 dynamic mechanical analyzer (DMA, TA Instruments, Inc., New Castle, DE, USA). The test mode was a single cantilever, the test frequency was 1 Hz, and the strain amplitude ranged from 0 to 6 × 10−4.

3. Results and Discussion

3.1. XRD

Figure 1 shows the XRD patterns of AlxCoCrFeNi HEAs powders and alloys with different Al contents. It can be seen from Figure 1 that the powder and alloy of Al0.2 possess a single FCC structure. With increasing the Al content, the Al0.5 powder has the structure of the FCC phase coexisting with the BCC. After SPS sintering, with the increase of Al content, the FCC phase structure and two BCC base structures appear in Al0.5 alloy. One is the disordered BCC phase structure, and the other is the ordered BCC phase (B2 phase) structure (indicated by the unique (100) and (111) super-lattice peaks) [43]. The Al1 powder is a single BCC phase structure. FCC, BCC, B2, and sigma (σ) phases (The σ phase is the tetragonal Fe-Cr phase) are observed in the Al1 alloy [12,44]. According to Rao et al. [45], the formation of the σ phase started at 870 K and disappeared at about 1236 K, depending on the Al content. It can be seen that in the Al0.5 and Al1 alloys, the B2(100)/BCC (110) and (211) peaks shift to the high angles with the increase of Al content, indicating that the increase of Al content can reduce lattice distortion. However, the FCC (111), (200), and (220) peaks move to the low angle side, which reflect the lattice distortion is aggravated by the high Al content, whose atomic radius is the largest among the five constituent elements in the solid solution [43]. The results indicate that the Al content increase affects the AlxCoCrFeNi alloy’s structure and promotes the formation of the BCC phase and other intermetallic phases (B2 and σ phases).

3.2. Microstructure

Figure 2 shows SEM back-scattering electron images of AlxCoCrFeNi alloys. In Figure 2, there are some microscopic holes on the surface of the sample, which is due to current inhomogeneity in the SPS sintering process, which causes the local current density at the sintering neck to be considerable and the temperature to be excessively high. Because the powder is volatile, micropores develop at higher sintering temperatures [11]. As indicated in Figure 2a,b, the uniformly distributed microstructure is exhibited in the Al0.2 alloy. At the same time, some microholes are observed, showing the formation of a single FCC solid solution phase. EDS results of different regions of the three samples are shown in Table 1. Based on the relative peak intensity in the XRD pattern and the EDS results, the white matrix part is the Fe-, Co-, and Cr-rich FCC phases. The SEM morphology of the Al0.5 alloy is shown in Figure 2c,d; the disordered BCC phase and the ordered BCC phase (B2 phase) precipitate in an irregular bulk/needle-like morphology when the Al content is increased from 0.2 to 0.5. The B2 phase is so similar to the disordered BCC phase that it is difficult to distinguish [43]. The bulk BCC/B2 phase ranges in size from 0.6 to 5 μm, and the needle-like BCC/B2 phase ranges in size from 0.3 to 2 μm in Figure 2d. Three different microstructures (white matrix phase, black irregular bulk phase, and needle-like phase) were formed in the Al0.5 alloy (see Figure 2c,d). Based on the XRD pattern and EDS results, the white matrix part is the FCC phase rich in Fe-, Co- and Cr, and the irregular bulk part and needle-like part are the Al-, Ni-rich B2 and BCC phase, which is consistent with previous studies [46,47]. As shown in Figure 2c, the BCC and the B2 phase consist of aggregate structures consisting of fine phase alternations, which were considered to be formed during the spinodal decomposition [37]. After increasing the Al content to 1, the irregular bulk and needle-like parts disappear, and the network and wall-shaped structure occurs as shown in Figure 2e,f, and the size of BCC and B2 phase was significantly coarsened. The nanoscale precipitates are observed in the matrix phase after increasing the Al content to 1. In Figure 2e,f, three phases with different contrast degrees are also observed: black phase, gray phase, and bright-white phase. Based on the EDS results in Table 1, the nanoscale precipitated phase is the BCC phase with elements close to equal molar ratio; the black phase is the Al-, Ni-rich B2 phase; the gray phase is FCC phase rich in Fe, Cr, and Co; and the bright-white phase is σ phase rich in Cr and Fe. The presence of the Cr element and the binary system of Cr-Co, Cr-Fe, and Cr-Ni contribute to the formation of σ phase in AlCoCrFeNi HEA [10,27,48].
Figure 3 represents the elemental mapping of the AlxCoCrFeNi HEAs. The element map provides information about the distribution of each element in the alloy. As shown in Figure 3a, all elements are uniformly distributed in the region, and there is no element segregation phenomenon in the alloy. This indicates that the Al0.2 alloy forms a single phase, namely FCC, which is consistent with the XRD and SEM analysis results. With an increase of the Al content from 0.2 to 0.5, BCC and B2 phases with two different morphologies (irregular bulk and needle-like) appear in the FCC matrix, as shown in Figure 3b. The enthalpy of mixing Al with other elements is more negative than that of the other atomic pairings of the system’s five primary components (the Al-Ni phase has high negative enthalpy), resulting in phase segregation effects [49]. As shown in Table 1, in the Al0.5 alloy, the atomic ratios of Al and Ni elements in bulk BCC/B2 phase are 25.71% and 29.07%, the atomic ratios of Al and Ni elements in the needle-like BCC/B2 phase are 25.15% and 30.85%, and the atomic ratios of Fe, Co and Cr elements in FCC phase are 24.04%, 22.80%, and 25.13%, respectively. This effect results in different phases having different shapes and compositions. In Figure 3c, the Al and Ni elements are mainly distributed in the black (B2) phase; Fe, Co, and Cr elements are mainly distributed in the gray (FCC) phase; and Cr and Fe elements are mainly distributed in the bright-white (σ) phase, which is consistent with Figure 2f and Table 1. Therefore, both Figure 3 and Table 1 show that the amount of Al plays a crucial role in forming and stabilizing the phase [50,51].
The TEM bright-field (BF) pictures and corresponding selected area electron diffraction (SAED) of Al1 HEA are shown in Figure 4. In the Al1 alloy (Figure 4), (a) and (b), in addition to the FCC phase and BCC/B2 phase, the σ phase with tetragonal structure in the BCC/B2 phase is also observed (Figure 4b), which also indicates that σ phase may have been transformed from the BCC/B2 phase [28]. Twin crystals with FCC structure are also found in Al1 alloy, as labeled in Figure 4a, which is consistent with previous studies [27].

3.3. Mechanical Properties

The engineering stress–strain curves of AlxCoCrFeNi HEA at room temperature are shown in Figure 5. Table 2 demonstrates the tensile properties, compactness, and hardness of the alloy. As shown in Figure 5, Al0.2 and Al0.5 alloys undergo plastic deformation, and Al1 brittle fracture. With the increase of Al content, the ultimate tensile strength (UTS) and elongation of HEAs increased first and then decreased sharply. The UTS increased from 491.9 MPa in the Al0.2 alloy to 954.4 MPa in the Al0.5 alloy, and then decreased to 245.3 MPa in the Al1 alloy. The elongation increases from 11.5% of the Al0.2 alloy to 32.2% of the Al0.5 alloy and then decreases to 0.7% of the Al1 alloy. When the Al content increases from 0.2 to 0.5, the yield strength (YS) also increases from 347.5 MPa to 557.7 Mpa, and no yield was found in the Al1 alloy. The higher the Al content, and element segregation, the lattice distortion is aggravated, the solution strengthening effect is enhanced, and the mechanical properties of the alloy are enhanced [37]. Nevertheless, due to the existence of the σ phase (the σ phase is a brittle intermetallic phase [52,53]) in the microstructure of the Al1 alloy), the UTS and elongation of Al1 alloy are very poor. The best combination of strength and toughness can be achieved when x = 0.5, which probably lies in the coexistence of BCC and FCC crystal structures. The phase structure varies with the different Al contents, reflecting that the phase structure plays an essential role in the strength and plasticity of the material system (Figure 2 and Figure 5).
The Al element is important in promoting the formation of the BCC phase [54], and the BCC phase is a hard phase in the HEAs [55]. The content of the BCC phase increases with the increase of the Al content (Figure 2), so the hardness value of the alloy increases with the increase of Al content (Table 2). The presence of the σ phase in the Al alloy further increases the hardness [53], making the hardness of the Al1 alloy reach 585.4 HV (417.2 HV increase compared with the Al0.2 alloy). Compared with other alloys (Figure 2), the Al0.2 alloy has more holes caused by insufficient sintering. Therefore, the compactness of the Al0.2 alloy is only about 92.2%, while the compactness of the Al0.5 and the Al1 alloy is higher than 98.8 %.
Figure 6 shows the typical fracture surfaces of AlxCoCrFeNi HEA with different Al content after tensile testing. The macroscopic fracture morphologies of the Al0.2, Al0.5, and Al1 alloys are shown in Figure 6a,e,i, respectively. The characteristic dimple features are seen in both the Al0.2 and the Al0.5 samples, indicating that the Al0.2 and Al0.5 alloys have both undergone considerable plastic deformation and have failed in a ductile fracture mode, with an elongation range of 11.5% to 32.2% as shown in Table 2. However, some typical tear ridges are observed in the Al1 sample (Figure 6j–l), and the fracture surfaces display the cleavage fracture morphology of the river pattern (Figure 6l), indicating that the Al1 alloy failed in the cleavage fracture mode with negligible tensile ductility, as showed in Table 2. Furthermore, clear micro-cavities and secondary cracks can be seen in all samples. The dimples in the Al0.5 alloy of Figure 6f–h are larger, and their number density is the largest, which is consistent with the maximum elongation (32.2%). Contrasted with the Al0.5 alloy, the dimples and their number density of the Al0.2 alloy in Figure 6b–d are modest, and the intergranular break can be tracked down in the neighborhood locale of Figure 6b–d. Besides, in Figure 6d,l (the Al0.2 and Al1 alloys), the second-phase particles can be observed, and when sufficient stress is applied to break the interfacial bond between the particles and the matrix, voids form around them, leading to eventual fracture [56]. Furthermore, a hard and brittle σ phase appears in the Al1 alloy. Accordingly, the Al0.2 alloy has a poor plasticity of 11.5%, while the Al1 alloy has the worst and negligible plasticity.
Figure 7 shows the variation of damping-strain amplitude for AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEA at a test frequency of 1 Hz. It is clear from Figure 7 that the damping characteristics of the sample increase with increasing strain amplitude. Among them, the damping performance of the Al0.5 sample is successively higher than that of the Al1 and Al0.2 samples in the whole range of strain amplitude. The Internal Friction Q−1 of the Al0.5 alloy is 0.018, and the corresponding strain amplitude is roughly 6 × 10−4, which surpasses many traditional damping alloys, like FeCr-based [57] and sintered MnCu-based alloys [58,59]. The damping characteristics of the two alloy systems are primarily due to the ferromagnetic damping and twin-boundary damping. Considering the phase composition and characteristics, it is speculated that the damping mechanism of the AlxCoCrFeNi high entropy alloy is mainly caused by the phase interface moving energy dissipation under the action of external force, especially the hard BCC phase and soft FCC phase moving energy dissipation under the action of external force [42].
Combining Figure 1 and Figure 2, it can be seen that a large number of needle-like and block-like BCC/B2 phases are precipitated in the Al0.5 sample. Under external force, the movement of the interface between the BCC/B2 phase and the FCC phase consumes energy, and the alloy has good damping performance. The BCC and B2 phases of the Al1 sample are coarsened, and the volume fraction of the FCC phase is significantly reduced, resulting in a reduction of the interface between the BCC/B2 phase and the FCC phase, so the damping performance is decreased compared with that of Al0.5. The Al0.2 sample is a FCC single-phase structure, with almost no phase interface movement energy dissipation, so the damping performance is the lowest. Under the same loading conditions, the ferromagnetic damping value of FeCr-based alloys was discovered to be dependent on the absolute value of the saturation magneto-striction coefficient [60]. The damping property of entropy alloy in AlxCrFeNi at low strain is related to the magnetostrictive effect caused by Fe and Cr elements [42]. Therefore, it is speculated that the Fe element and the Cr element, enriched in the FCC phase of AlxCoCrFeNi alloy, also contribute to the damping properties of the alloy. At the same time, the twin structure observed in the transmission pattern in Figure 4 can also contribute to the damping properties of the alloy [58].

4. Conclusions

In this study, the microstructure, mechanical properties, and damping capacity of AlxCoCrFeNi (x = 0.2, 0.5, and 1) high-entropy alloys prepared by spark-plasma sintering were systematically studied. The results of the study are as follows:
The increase in Al content results in a difference in the phase structure of the alloys, from a single FCC phase (Al0.2 alloy) to FCC + BCC + B2 phase (Al0.5 alloy), and then to FCC + BCC + B2 + sigma (σ) phase structure (Al1 alloy). Twins with FCC structure were also observed in the Al1 alloy.
The tensile properties of the alloy show a trend of increasing and then decreasing with the increase of Al content. Among them, the yield strength, ultimate tensile strength, and elongation of Al0.5 alloy reached the highest, which were 557.7 MP, 954.4 MPa, and 32.2%, respectively.
The alloy’s hardness increases with the Al content’s increase, and the hardness of Al1 reaches the highest value of 585.4 HV (417.2 HV higher than the Al0.2 alloy). The compactness of the alloy is proportional to the increment of the Al element. The compactness of the Al0.2 alloy is only 92.2%, while in the Al0.5 and Al1 alloy, it is above 98.8%.
Fracture results show that the fracture mechanism of the Al0.2 and Al0.5 alloys are typical ductile fractures, while the fracture mechanism of the Al1 alloy is a cleavage fracture.
The Al0.5 HEA with FCC, BCC, and B2 phases as substrates obtained the highest damping capacity of 0.018 at a corresponding strain amplitude of 6 × 10−4, which is higher than many conventional damping alloys such as FeCr-based and sintered MnCu-based alloys.

Author Contributions

Conceptualization, K.X., L.H. and W.F.; methodology, K.X. and L.H.; validation, K.X. and X.W.; formal analysis, L.H., K.X. and L.Y.; investigation, K.X., X.W. and L.Y.; resources, W.F. and L.H.; data curation, K.X. and L.H.; writing—original draft preparation, L.H. and K.X.; writing—review and editing, K.X., X.W. and L.H.; visualization, W.F.; supervision, L.H. and W.F.; project administration, W.F.; funding acquisition, L.H. and W.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XRD patterns of AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEAs powders and alloys.
Figure 1. XRD patterns of AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEAs powders and alloys.
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Figure 2. The SEM back scattering electron images of AlxCoCrFeNi HEAs. (a,b): Al0.2CoCrFeNi; (c,d): Al0.5CoCrFeNi; (e,f): AlCoCrFeNi.
Figure 2. The SEM back scattering electron images of AlxCoCrFeNi HEAs. (a,b): Al0.2CoCrFeNi; (c,d): Al0.5CoCrFeNi; (e,f): AlCoCrFeNi.
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Figure 3. The elemental mapping of the of AlxCoCrFeNi HEAs: (a) Al0.2CoCrFeNi, (b) Al0.5CoCrFeNi, and (c) AlCoCrFeNi. The elemental distribution of Al, Co, Cr, Fe, and Ni are shown in red, purple, green, blue, and yellow, respectively.
Figure 3. The elemental mapping of the of AlxCoCrFeNi HEAs: (a) Al0.2CoCrFeNi, (b) Al0.5CoCrFeNi, and (c) AlCoCrFeNi. The elemental distribution of Al, Co, Cr, Fe, and Ni are shown in red, purple, green, blue, and yellow, respectively.
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Figure 4. TEM bright-field (BF) images (a) and the corresponding selected area electron diffraction (SAED) patterns (b) of Al1 HEA.
Figure 4. TEM bright-field (BF) images (a) and the corresponding selected area electron diffraction (SAED) patterns (b) of Al1 HEA.
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Figure 5. Tensile engineering stress–strain curves of AlxCoCrFeNi HEAs at room temperature. (The gauge length is 5 mm, while the width and thickness are 1.5 mm and 1 mm, respectively. The strain rate is 0.2 mm/min).
Figure 5. Tensile engineering stress–strain curves of AlxCoCrFeNi HEAs at room temperature. (The gauge length is 5 mm, while the width and thickness are 1.5 mm and 1 mm, respectively. The strain rate is 0.2 mm/min).
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Figure 6. Tensile fractographs of (a–d) Al0.2 HEA; (e–h) Al0.5 HEA; and (i–l) Al1 HEA.
Figure 6. Tensile fractographs of (a–d) Al0.2 HEA; (e–h) Al0.5 HEA; and (i–l) Al1 HEA.
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Figure 7. The damping-strain amplitude diagram of the AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEAs at a test frequency of 1 Hz.
Figure 7. The damping-strain amplitude diagram of the AlxCoCrFeNi (x = 0.2, 0.5 and 1) HEAs at a test frequency of 1 Hz.
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Table
Table 1. EDS analysis results of AlxCoCrFeNi HEA (unit: at %), see Figure 2 for the specific phases.
Table 1. EDS analysis results of AlxCoCrFeNi HEA (unit: at %), see Figure 2 for the specific phases.
AlxCoCrFeNiRegionsPhaseChemical Composition (at. %)
AlCoCrFeNi
Al0.2White matrixFCC4.0824.0624.2724.0623.53
Al0.5White matrixFCC7.8322.8025.1324.0420.20
Irregular bulkB2/BCC25.7117.4213.1214.6829.07
Needle-likeB2/BCC25.1517.8311.8514.3230.85
Al1GrayFCC6.2925.4523.5626.5618.14
PrecipitatesBCC21.4819.8418.2618.7521.67
BlackB227.8612.0615.7418.6525.69
Bright-whiteσ8.1918.1737.6328.347.67
Table
Table 2. Mechanical properties of AlxCoCrFeNi HEAs.
Table 2. Mechanical properties of AlxCoCrFeNi HEAs.
AlxCoCrFeNiYS (MPa)UTS (MPa)Elongation (%)Hardness (HV)Compactness (%)
Al0.2347.5 ± 3491.9 ± 511.5 ± 0.3168.2 ± 492.2 ± 0.6
Al0.5557.7 ± 5954.4 ± 932.2 ± 0.5280.8 ± 599.2 ± 0.2
Al1-245.3 ± 30.7 ± 0.1585.4 ± 998.8 ± 0.3
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Xiong, K.; Huang, L.; Wang, X.; Yu, L.; Feng, W. Microstructure, Mechanical Properties, and Damping Capacity of AlxCoCrFeNi High-Entropy Alloys Prepared by Spark Plasma Sintering. Metals 2022, 12, 2058. https://doi.org/10.3390/met12122058

AMA Style

Xiong K, Huang L, Wang X, Yu L, Feng W. Microstructure, Mechanical Properties, and Damping Capacity of AlxCoCrFeNi High-Entropy Alloys Prepared by Spark Plasma Sintering. Metals. 2022; 12(12):2058. https://doi.org/10.3390/met12122058

Chicago/Turabian Style

Xiong, Ke, Lin Huang, Xiaofeng Wang, Lin Yu, and Wei Feng. 2022. "Microstructure, Mechanical Properties, and Damping Capacity of AlxCoCrFeNi High-Entropy Alloys Prepared by Spark Plasma Sintering" Metals 12, no. 12: 2058. https://doi.org/10.3390/met12122058

APA Style

Xiong, K., Huang, L., Wang, X., Yu, L., & Feng, W. (2022). Microstructure, Mechanical Properties, and Damping Capacity of AlxCoCrFeNi High-Entropy Alloys Prepared by Spark Plasma Sintering. Metals, 12(12), 2058. https://doi.org/10.3390/met12122058

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