Phase Prediction, Microstructure and Mechanical Properties of Fe–Mn–Ni–Cr–Al–Si High Entropy Alloys

Abstract

The selection of high-entropy alloys (HEAs), which are relatively lightweight and have unique mechanical properties, remains a substantial challenge. In this study, six new HEAs were designed from the relatively low-cost Fe–Mn–Ni–Cr–Al–Si system using Thermo-Calc software, and then manufactured using a casting process. The effects of the atomic ratio of the alloying elements on the microstructures and mechanical properties of these alloys in the as-cast condition were systematically investigated. Brittle body-centered cubic BCC/B2 and silicide phases were found in relatively large amounts in the form of dendritic structure within large equiaxed grains with fine needle-shaped phases in the Fe₃₀Mn₁₅Ni₂₀Cr₁₅Al₁₀Si₁₀ and Fe₃₅Mn₁₅Ni₂₀Cr₁₅Al₁₀Si₅ alloys, in addition to the face-centered cubic (FCC) phase. When the contents of Mn and Ni were increased in the Fe₃₅Mn₂₅Ni₁₅Cr₁₅Al₅Si₅ and Fe₃₅Mn₂₀Ni₂₀Cr₁₅Al₅Si₅ alloys, the amounts of brittle phases were reduced; however, the ductile FCC phase is not significant. The FCC phase amount, which appeared as a honeycombed structure, was more than enough when the Si content was decreased to 3%. Broad relationships between the chemical composition of the alloys, especially the Si content, and the hardness and compression properties’ measurements were established. As the Si content decreased, both the hardness and compression properties of the resulting alloy also decreased. The experimental observation of the six HEAs matched the equilibrium phases predicted by the Thermo-Calc calculations.

1. Introduction

High-entropy alloys (HEAs) have attracted many researchers’ attention since 2004, after Jien-Wei Yeh and Brian Cantor [1,2] achieved good results from them in their work. High-entropy alloys (HEAs) can be defined as multi-metallic materials, containing four or more basic alloying elements in equal atomic percentages (at.%) or near-equiatomic proportions [3,4]. The atomic portion of each element is often in excess of 5 at.%. This design philosophy was initially aimed at stabilizing the massive solid solutions of a single phase over high configurational entropy. These newly designed alloys have exceptional mechanical properties, which may vary entirely from their basic elements [5,6,7,8]. HEAs are a favored approach for the production of high-performance alloys with improved mechanical toughness and strength, higher thermal stability, enhanced oxidation, soft magnetic properties, and corrosion resistance [9,10,11,12]. In addition, several HEAs have shown high resistance to irradiation, exhibiting lower irradiation-stimulated segregation and reduced density of dislocation loops, compared to ordinary alloys [13,14], and possessing self-healing properties [15,16]. These unique properties position them as the first choice for structural applications, especially in the improvement of power plants’ efficiency, which need to employ novel materials that can withstand extreme working conditions, particularly for the new generation of nuclear fission. On the other hand, other HEAs show both high wear and corrosion resistance, accepted mechanical properties, and high biocompatibility, in addition to the low cost, which make these HEAs favorable candidates for biomedical implantation materials [17,18,19,20]. Furthermore, a metal film of HEAs with accepted toughness, electrical resistivity, and high fatigue performance could also be a promising candidate for flexible electronic devices [21]. Another HEA shows excellent thorough properties including accepted mechanical properties, excellent antifouling abilities, outstanding resistance to wear and corrosion for marine applications [22]. Moreover, the mechanical properties of high-entropy alloys (HEAs) can be improved significantly by thermo-mechanical processing, which gives these alloys unique properties, making them vastly suitable for different applications as described by Wani et al. [23]. For example, the recent study on the AlCoCrFeNi2.1 high-entropy alloy with eutectic structure [24,25], tensile strength > 1000 MPa, and ductility of 10% was obtained by rolling the ingot to a reduction ratio of up to 90% and then annealing at a temperature of 1200 °C. Further examples of these multi-component alloys are Fe₄₀Mn₄₀Co₁₀Cr₁₀ HEAs, produced by Deng et al. [26], and the same alloy with Ni addition, Fe₄₀Mn₂₇Ni₂₆Co₅Cr₂, studied by Yao et al. [27]. They elucidated that these types of alloys have superior mechanical properties analogous to some types of tool steels. Another study suggested inserting Al into these alloys in the state of Co to improve the mechanical properties and to achieve cost reduction [28,29]. On the other hand, Li et al. improved the hardness and corrosion resistance of the FeCoNiCrCu_0.5 alloy by adding 1.5 at.% Al. In another study, N.D. Stepanov et al. [30] studied the effect of an Al fraction on the microstructure and mechanical properties of the Fe–Mn–Cr–Ni–Al non-equiatomic high-entropy alloys system with various Al percentages (x = 0–14 at.%). They found that an Al addition to a BCC-prone Fe₄₀Mn₂₅Cr₂₀Ni₁₅ alloy is useful for the improvement of the studied alloys with the mixture of bcc matrix and the inserted B2 precipitation showing promising mechanical properties. Cui et al. [31] showed that the addition of Al 0.77 at.% to the FeCrNiAlx HEA established it as a promising material for application in aerospace fields, due to its high specific strength and accepted ductility at high temperatures. Moreover, Kishore et al. [32] investigated the effect of the addition of Mn to an equi-atomic CoCrNi alloy. They concluded that a Mn addition enhanced the hardening ability because of the steep increase in hardness (~650 Hv in Co₃₃Ni₃₃Cr₁₉Mn₁₅ alloy vs. ~610 Hv in CoCrNi alloy). In addition, Oh et al. [33] stated that the addition of Mn increases the fraction of the BCC phase and, as a result, the nanohardness in the HEA AlCoCrFeN also increases. In another high-entropy alloy, Fe₄₀Co₄₀Ni₁₀M₁₀ (M = Al, Mn) [34], Al addition was useful for obtaining a complete BCC structure formation using the casting process. On the other hand, Mn produces dual phase development with high mechanical properties as a result of grain refinement. Meng et al. [35] investigated the effect of Cr on the mechanical properties of Fe₃₀Ni₂₀Mn₃₅Al₁₅. They elucidated that the ductility at room temperature increased with increasing the Cr content to 6 at.%, because the addition of Cr caused the complete deactivation of the environmental embrittlement. Gu et al. [36] studied the effect of Si addition to the Al0.3 CoCrFeNi high-entropy alloy. They clarified that adding Si could increase the hardness and strength of alloys. They concluded that Si addition increases the development of a new (Al, Ni, Si) rich phase with a B2 structure (BCC1 phase), and a (Fe, Cr)₃Si phase with L21 structure (BCC2 phase). Guo et al. [37] explained that the addition of Si to TaMo_0.5NbZrTi_1.5Al_0.1 enables significant grain refinement and development of intergranular silicides after annealing. Furthermore, they mentioned that the Si addition improves the mechanical properties alongside increasing the deformability of the alloy by facilitating the development of fine silicides and the extra solute effects. Xu et al. [38] showed that the Si addition could manipulate the microstructure of VNbTiTaSix and, in turn, improve the mechanical properties when the Si addition reaches 10%. In the coating domain, Liu et al. [39] investigated the effect of adding Si to the AlCoCrFeNiSix coatings. They found that the enhancement of microhardness was controlled by the influence of dislocation strengthening, rather than fine structure strengthening and solution strengthening. Additionally, the wear resistance was enhanced due to the formation of different oxides including SiO₂ and SiO. On the other hand, Ma et al. [40] concluded that at high temperatures adding Si improves the phase stability of the CoCr2FeNb0.5Ni coating by reducing the interplanar distance of the crystal planes. In addition, the formation of the (Cr, Si)Ox amorphous oxide layer can inhibit oxygen from diffusing inwards, and hence increase the high temperature oxidation resistance. Huang et al. [41] explained that the Si addition improved both the microhardness and wear resistance of the FeCoCrNiSix alloys. The improvement in the microhardness can be related to the formation of BCC phase because of the addition of Si. Hou et al. [42] studied the effect of adding Si to the metastable Fe₅₀Mn₃₀Co₁₀Cr₁₀ and found that significant improvement in toughness occurred in the SLMed metastable high-entropy alloy. This improvement can be related to the numerous deformation mechanisms included because the addition of Si. Guo et al. [43] found that adding Ni improved the mechanical properties of the AlCoCrFeTi_0.5 high-entropy alloys by achieving dual phase structure. Qiu et al. [44] studied the effect of Fe fraction in four FexCoNiCu HEAs and found that, by increasing the Fe fraction, the crystal structure of the alloys progressively altered from FCC to a mixture of BCC and FCC phases. In addition, the deformation mechanism can be manipulated via controlling the chemical composition of the HEAs alloys. For example, Huang et al. [45] studied the effect of the Ta composition on the deformation mechanism of the TiZrHfTaX (x = 1, 0.8, 0.6, 0.5) alloys. They found that, by reducing the percentage of Ta, both TWIP and TRIP strengthening mechanisms are included. Furthermore, Xiaoyi et al. [46] studied the Mo and Nb composition effect on the mechanical properties of the AlCrFe₂Ni₂(MoNb)x alloys and deduced that Mo and Nb content in the range 0.1–0.7 increased yield strength in compression (from 878 MPa to 1549 MPa) though the plastic strain from 43.7% to 8.6%. The design of new high-performance HEAs has been attracting much attention from researchers recently. However, HEAs have intrinsic properties of sluggish diffusion. Therefore, the equilibrium phase formation may be kinetically very hard to achieve. Therefore, there are many empirical methodologies to predict phase formation in HEAs based on the aforementioned research. Among these methodologies are thermodynamic parameters, and recently machine learning, as discussed elsewhere.

In this work, we investigate different non-equiatomic FeAlNiCrMnSi HEA compositions. The new alloys are close in composition to high-Mn stainless steel. Fe, Ni, and Cr elements are the main elements of stainless steel. In addition, Mn is used as an austenite stabilizer. Al and Si elements are used to improve the mechanical and chemical properties as well as to decrease the density. Various characterization methods were applied to characterize the new alloys’ microstructure and phase composition. The phase formation in HEAs is controlled by different factors. The thermodynamic parameters, such as mixed entropy $(\Delta S_{mix})$, mixing enthalpy $(\Delta H_{mix})$, Gibbs free energy $(\Delta G_{mix})$, valence electron concentration (VEC), and others have direct relation to the phase formation. Empirically, VEC can provide an idea about the formed phases. For example, single FCC and BCC solid solution phases form when VEC ≥ 8 and VEC < 6.87, respectively, while a mixture of FCC and BCC solid solution phases are expected if 6.87 ≤ VEC < 8, as reported in [47]. However, in this work, we aim to connect the equilibrium phase formation in this type of low-cost Fe–Cr–Mn–Ni–Al–Si high-entropy alloy system, predicted by Thermo-Calc TCHEA software, with the formed equilibrium/nonequilibrium phases during real solidification process without further treatment process.

2. Materials and Methods

Six new FeMnNiCrAlSi high-entropy alloys (HEAs) were designed using a platform of Thermo-Calc software (Version 2022a, THERMOCALC TCHEA6, Stockholm, Sweden) equipped with a HEA database (TCHEA2021). The effect of the contents of the different elements of the alloys in the as-cast condition on the phase constituents, microstructure, and hardness of the resulting materials was studied. The new HEAs were prepared from the following elements of Fe, Mn, Ni, Cr, Al, and Si according to the chemical composition in Table 1 using an electric arc furnace (ARCAST 200, Maine, ME, USA) under a high-purity argon atmosphere. First, the ingots were produced using high-purity elemental Fe (99.99%) shot, Mn (99.95%) flake, Ni (99.95%) granule, Cr (99.95%) granule, Al (99.96%) wire, and Si (99.99%) granule. To ensure full melting and the homogeneity of the ingot, it was melted 4 times by using an electromagnetic stirrer and flipping each time. Before the microstructural analysis, metallographic procedures, which include grinding, polishing, and etching, were applied to the samples. The microstructure investigation was carried out using an optical microscope after electrochemical etching with 10% Oxalic acid. X-ray diffraction (Model-6100, Shimadzu, Kyoto, Japan) was used in the scanning range of 20° ≤ 2θ ≤ 80° intervals with a step size of 0.05 deg. The scan rate of 1 deg./s was used to investigate the crystal structure of the six alloys in the as-cast condition. A Shimadzu microhardness tester (Shimadzu, Kyoto, Japan) was used to measure the microhardness with a testing load 5 N, and the time of indentation was 30 s. An average of 5 indents was taken for each condition. The compression tests were carried out on the alloys using the (AGS-X, Shimadzu) universal testing machine (Shimadzu, Kyoto, Japan) at a strain rate of 10⁻³ s⁻¹ to an engineering strain of 0.4 on cylindrical specimens Ø5 mm × 7 mm in size.

3. Results and Discussion

3.1. Phase Constitution

The Thermo-Calc software phase prediction of the alloy Fe₃₀Mn₁₅Ni₂₀Cr₁₅Al₁₀Si₁₀ (Alloy 1) shows the formation of the brittle BCC (B2) phase at first to solidify phase in addition to silicides, such as MnNiSi and CrSi intermetallic compounds phases, as shown in Figure 1. This is due to the high percentage of Si, which promotes the formation of the brittle BCC (B2) phase. At the same time, the high content of Al (10 at.%) plays a significant role as a BCC stabilizer. This was confirmed by the XRD analysis shown in Figure 2, which clearly shows BCC (B2) is the main phase beside some unknown peaks, which is most probably due to silicides and/or sigma phase formation during solidification.

When the Si content was decreased to 5 at.% and the Fe was increased to 35 at.% in Alloy 2 (Fe₃₅Mn₁₅Ni₂₀Cr₁₅Al₁₀Si₅), the FCC phase beside the BCC phases were detected as predicted to appear during solidification in the Thermo-Calc chart shown in Figure 3. This is also confirmed with the XRD peaks in Figure 2. These two alloys (Alloy 1 and 2) were very brittle and broke during the processing of the cast ingot. To increase the ratio of the ductile FCC phase, the content of Mn, which is an FCC stabilizer, was increased from 15 at.% to 25 at.% in Alloy 3 (Fe₃₅Mn₂₅Ni₁₅Cr₁₅Al₅Si₅) at the expense of Al and Ni. The phase prediction of Alloy 3 is shown in Figure 4. There was a reasonable amount of the FCC phase appearing during the solidification process at a temperature close to the solidus line. However, the brittle B2 structure is still the main phase in Alloy 3, as well as formation of silicides at high temperature close to the melting point. The fourth trial was to increase the FCC fraction by increasing the Ni content, a strong FCC stabilizer, to 20 at.% as in Alloy 4 (Fe₃₅Mn₂₀Ni₂₀Cr₁₅Al₅Si₅) at the expense of the Mn content. The Thermo-Calc calculation of this Alloy 4, Figure 5, predicts the formation of the BCC phases—first solid to form; however, the ductile FCC phase is the main phase at the end of the solidification process. Further reductions in the Si content to 3 at.% while increasing the Ni content in Alloy 5 (Fe₃₅Mn₂₀Ni₂₂Cr₁₅Al₅Si₃) led to a delay in the formation of the silicides at high temperatures; the results are shown in Figure 6. The alloy contained mainly the FCC phase, and a small amount of B2 phase was expected while the silicides precipitation was delayed at lower temperatures. According to Figure 6, Alloy 5 would have full FCC phases at high temperatures before sigma; whereas silicides precipitate at lower temperatures. Alloy 5 is expected to have good deformability, and it showed high cold workability compared to Alloys 1–4, as will be explained in a different work.

Alloy 6 (Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃) represents the last trial of this study, as shown in Figure 7. The aim with Alloy 6 was to increase the strength by increasing the BCC phase fraction by a slight increase in the Cr content to be 16 at.% and reducing Ni back to 20 at.%, while maintaining less silicide formation by keeping Si content as its lower content of 3%. In Alloy 6, the FCC phase became the main constituent, and a slightly higher amount of B2 phase was observed compared to Alloy 5, and no silicides present at high temperature. Alloy 6 was also deformable and the results will be presented elsewhere. The phase identification of the 6 alloys in the study was carried out by XRD. Figure 2 shows a high degree of consensus with the phase constitution of the alloys predicted by Thermo-Calc in Figure 1, Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7, as explained below.

3.2. Microstructure Characterization

Figure 8 shows the microstructure of HEAs (Alloys 1–3). In Alloy 1, dendritic structure within large equiaxed grains with fine, needle-shaped phases was the matrix of this alloy along with the white BCC phase. This is due to the high percentage of Si, which promotes the formation of this kind of needle-like silicide structures. According to the XRD results and the Thermo-Calc prediction, Alloy 1 consists mainly of BCC/B2 and silicide phases, which is a very hard and brittle mixture. The dark, round, fine phase may be a different type of silicide formed by precipitation in solid state at high temperatures, according to XRD results and the Thermo-Calc prediction in Figure 1.

According to many published works, the high content of Al (10 at.%) can form aluminides (Si does the same), which act as heterogenous nucleation sites during solidification leading to the formation of equiaxed grain microstructures [48]. For Alloy 2 (Fe₃₅Mn₁₅Ni₂₀Cr₁₅Al₁₀Si₅), BCC/B2 grains were observed together with very fine precipitates, as shown in Figure 8b. According to XRD in Figure 2, BCC/B2 is the main phase, and fine FCC and B2 phases may be formed during cooling, matching the Thermo-Calc prediction. Generally, the higher amount of Al (in Alloys 1 and 2) enhanced the formation of BCC phases, as reported by Singh et al. [49]. A semi- honeycomb BCC structure with fine arms (dendritic structure) was observed in Alloy 3 (Fe₃₅Mn₂₅Ni₁₅Cr₁₅Al₅Si₅) to be distributed in a matrix of FCC phase, as shown in Figure 8c. Fine, dark, minor phases were observed which may be related to silicide formation during cooling in the solid state as in Alloy 1 and 2. For the structure of Alloy 4 (Fe₃₅Mn₂₀Ni₂₀Cr₁₅Al₅Si₅), dendritic FCC grains were observed as shown in Figure 9a. Small amounts of the darker brittle BCC phase were detected in the inter-dendrite zone. However, the XRD results reported that the BCC phase would be a minor phase while an unknown phase was quite detectable. In the microstructure of Alloy 4 in Figure 9a, there are two inter-dendrite phases: one is in gray color and the other is in black. These unknown phases may be silicides formed by precipitation in the solid state during cooling and/or the BCC/B2 phases. Further studies are needed to clarify this issue.

The structure of Alloy 5 (Fe₃₅Mn₂₀Ni₂₂Cr₁₅Al₅Si₃) consisted of a large columnar and dendritic grains of mainly the FCC phase, as shown in Figure 9b. The high FCC phase constitution in the alloy is due to high Ni and Mn content and less Al and Si content. Minor, aligned, black, droplet-shaped phases were precipitated in the inter-dendritic zones. These minor, black, droplet-shaped phases were most probably formed during cooling in the solid state and may be silicides or Al-Ni-rich phases [48], even though only the FCC phase was detected by XRD in Alloy 5. In accordance with this, Alloy 5 contains the biggest amount of the FCC phase among the six studied alloys, as predicted by Thermo-Calc where the FCC phase becomes the only solid phase at high temperature range. Therefore, Alloy 5 would be softer than others and shows high deformability.

The structure of Alloy 6, with a slightly higher amount of Cr while keeping low content of Al and Si (Alloy 6 with Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ system), showed a honeycomb dendritic structure consisting mainly of the FCC phase, as shown in Figure 9c. Higher precipitates than in Alloy 5 appeared on the boundary of the grains and concentrated on the triple point of grain boundaries in Alloy 6. These are most often the BCC/B2 phases as required from the design and proven by the XRD results. Almost all microstructural observations of the present six alloys were in good agreement with the Thermo-Calc calculations predictions and the XRD patterns.

3.3. Mechanical Properties

The microhardness of the six HEAs under investigation was measured using a Vickers microhardness tester, and the results are shown in Figure 10. It is clear that the hardness is noticeably affected by the chemical composition of the alloy. It can be seen that the key factor in the increase in hardness is the Si and Al fractions. Firstly, hardness decreased with decreasing both Si and Al fractions. This clearly appeared in the remarkably high hardness values of Alloy 1 and Alloy 2, which have high Al and Si contents. Al and Si stabilize the hard BCC phases. Additionally, they restrict the formation of the ductile FCC phase. Moreover, hard silicide intermetallics can easily form, which can harden these higher Si content alloys. Even when the Si content was reduced to half the amount in Alloy 2, the other strong BCC phase stabilizer (Al) increases the hardness to almost 500 HV. When both of them (Al and Si) were reduced to 5 at.% in Alloy 3 and Alloy 4, the hardness values were reduced to about 350 HV and 250 HV, respectively. Reduction in Al and Si provide the opportunity for the ductile FCC phase to form and reduce the hardness. The difference in hardness between Alloy 3 and Alloy 4 comes from the amount of formed FCC phase during solidification. Alloy 4 has a higher Ni content (20 at.%), which is a strong FCC phase stabilizer. When the Si content was reduced further to 3 at.% in Alloy 5 and Alloy 6, the hard silicides almost disappeared and the amount of the ductile FCC phase became the main constituent of the structure alongside a small amount of the brittle BCC (B2) phase. This results in a reduction in hardness to less than 200 HV, and provides a chance for it to be easily cold-deformed.

For more clarification of the mechanical properties, compression tests of the six alloys in their as-cast condition were performed and the results are shown in Figure 11. Firstly, it is important to record here that the casting defects such as pores, segregation, and uneven residual stresses can negatively impact the mechanical properties [50]. Alloy 1 was damaged during the test due to its higher brittleness. This was expected due to the ultra-high content of Al (10 at.%) and Si (10 at.%). The ultimate compression strength increases with higher Al and moderate Si content (Alloy 2) due to the formation of higher volume fractions of BCC phases. It reached as high as 1700 MPa. The compressive ductility often decreased when the strength increased. The ductility is very sensitive to the number of brittle phases, such as the BCC phase and other intermetallics. Therefore, the ductility of Alloy 1 was very low to the point of being broken during the initial stages of the test, while Alloy 2 shows ductility of only 10%. By reducing the amount of Al and Si by half, the ultimate strength reduced to almost half, about 900 MPa, and the ductility was increased to about 17% in Alloy 4. Unexpected results were recorded for Alloy 5 and 6, with higher values of compressive ultimate strength of about 1000 MPa. The formation of FCC phase with higher volume fraction increased the ductility to 25%. At the same time, the honeycomb dendritic structure increased the strength. In addition, the B2 precipitates that appeared in the triple point of grain boundaries act as obstacles against fracture during the test and increased the strength to 950 MPa for Alloy 6.

4. Conclusions

In this study, the effect of changing the fraction of alloying elements on the microstructures, and the mechanical properties of these alloys in the as-cast condition, were systematically investigated. The Thermo-Calc software was very efficient in predicting the phases in the as-cast condition, as confirmed by the experimental results. The first solid phases predicted to form during cooling from melt state are in all likelihood the present phases at room temperature. The major results of this study can be summarized as follows:

• Alloys with high Si fraction (Alloy 1 and Alloy 2) have mainly brittle silicides and BCC/B2 phases, and showed high hardness with values more than 750 Hv.

• The Si addition has a crucial role in the compression properties of the Fe–Mn–Ni–Cr–Al–Si HEAs system; as the Si addition increased, the compression strength increased and the ductility decreased.

• Decreasing the Si and Al content, while increasing the Mn and Ni contents to work as FCC stabilizing elements in Alloys 3, 5 and 6, caused the amounts of brittle phases were to be significantly reduced, and the ductile FCC phase was maintained as the main phase at room temperature. This resulted in hardness as low as 190 Hv.

• The microstructure and hardness can be easily manipulated in easy deformable Fe–Cr–Mn–Ni–Al–Si alloys by changing the alloying elements’ content while keeping Al at 5 at.% and Si at 3 at.%.

• There was a good consensus between experimental observations in the six high-entropy alloys and the equilibrium phase diagram predicted by the Thermo-Calc calculations.

Author Contributions

Conceptualization, E.R.I.M.; methodology, E.R.I.M. and A.S.; validation, S.E. and M.A.G.; formal Analysis, M.A.G. and E.R.I.M.; investigation, E.R.I.M.; data curation, S.E.; writing—original draft preparation, E.R.I.M. and S.E.; writing—review and editing, M.A.G.; supervision, M.A.G.; project administration, S.E.; funding acquisition, E.R.I.M. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to express their appreciation for the support provided by the Scientific Research Deanship, Islamic University of Madinah, with Tamayyuz—2 grant number 714.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures and Table

Figure 1. Phase diagram of Alloy 1 (Fe30Mn15Ni20Cr15Al10Si10) HEA.

Figure 2. XRD patterns of the as-cast six HEAs.

Figure 3. Phase diagram of Alloy 2 (Fe35Mn15Ni20Cr15Al10Si5) HEA.

Figure 4. Phase diagram of Alloy 3 (Fe35Mn25Ni15Cr15Al5Si5) HEA.

Figure 5. Phase diagram of Alloy 4 (Fe35Mn20Ni20Cr15Al5Si5) HEA.

Figure 6. Phase diagram of Alloy 5 (Fe35Mn20Ni22Cr15Al5Si3) HEAs.

Figure 7. Phase diagram of Alloy 6 (Fe36Mn20Ni20Cr16Al5Si3) HEAs.

Figure 8. Microstructural images of as-cast HEAs (a) Alloy 1, (b) Alloy 2, and (c) Alloy 3. Low and high magnification are presented in left and right, respectively.

Figure 9. Microstructural images of as-cast HEAs (a) Alloy 4, (b) Alloy 5, and (c) Alloy 6. Low and high magnification are presented in left and right, respectively.

Figure 10. Microhardness of the as-cast six Fe–Mn–Ni–Cr–Al–Si HEAs.

Figure 11. Typical true stress–strain curves of compression for the as-cast six Fe–Mn–Ni–Cr–Al–Si HEAs.

Table 1

The chemical composition of FeMnNiCrAlSi HEA alloys (at.%).

Alloy	Fe	Mn	Ni	Cr	Al	Si
1	30	15	20	15	10	10
2	35	15	20	15	10	5
3	35	25	15	15	5	5
4	35	20	20	15	5	5
5	35	20	22	15	5	3
6	36	20	20	16	5	3

References

1. Yeh, J.W.; Chen, S.K.; Lin, S.J.; Gan, J.Y.; Chin, T.S.; Shun, T.T.; Tsau, C.H.; Chang, S.Y. Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes. Adv. Eng. Mater.; 2004; 6, pp. 299-303. [DOI: https://dx.doi.org/10.1002/adem.200300567]

2. Cantor, B.; Chang, I.T.H.; Knight, P.; Vincent, A.J.B. Microstructural development in equiatomic multicomponent alloys. Mater. Sci. Eng. A; 2004; 375–377, pp. 213-218. [DOI: https://dx.doi.org/10.1016/j.msea.2003.10.257]

3. Li, Z.; Ludwig, A.; Savan, A.; Springer, H.; Raabe, D. Combinatorial metallurgical synthesis and processing of high-entropy alloys. J. Mater. Res.; 2018; 33, pp. 3156-3169. [DOI: https://dx.doi.org/10.1557/jmr.2018.214]

4. Otto, F.; Dlouhý, A.; Somsen, C.; Bei, H.; Eggeler, G.; George, E.P. The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy. Acta Mater.; 2013; 61, pp. 5743-5755. [DOI: https://dx.doi.org/10.1016/j.actamat.2013.06.018]

5. Miracle, D.B.; Senkov, O.N. A critical review of high entropy alloys and related concepts. Acta Mater.; 2017; 122, pp. 448-511. [DOI: https://dx.doi.org/10.1016/j.actamat.2016.08.081]

6. Bian, B.B.; Guo, N.; Yang, H.J.; Guo, R.P.; Yang, L.; Wu, Y.C.; Qiao, J.W. A novel cobalt-free FeMnCrNi medium-entropy alloy with exceptional yield strength and ductility at cryogenic temperature. J. Alloys Compd.; 2020; 827, 153981. [DOI: https://dx.doi.org/10.1016/j.jallcom.2020.153981]

7. Liu, D.; Jin, X.; Guo, N.; Liaw, P.K.; Qiao, J.W. Non-equiatomic FeMnCrNiAl high-entropy alloys with heterogeneous structures for strength and ductility combination. Mater. Sci. Eng. A; 2021; 818, 141386. [DOI: https://dx.doi.org/10.1016/j.msea.2021.141386]

8. Elkatatny, S.; Gepreel, M.A.H.; Hamada, A.; Nakamura, K.; Yamanaka, K.; Chiba, A. Effect of Al content and cold rolling on the microstructure and mechanical properties of Al₅Cr₁₂Fe₃₅Mn₂₈Ni₂₀ high-entropy alloy. Mater. Sci. Eng. A; 2019; 759, pp. 380-390. [DOI: https://dx.doi.org/10.1016/j.msea.2019.05.056]

9. Mishra, R.K.; Sahay, P.P.; Shahi, R.R. Alloying, magnetic and corrosion behavior of AlCrFeMnNiTi high entropy alloy. J. Mater. Sci.; 2019; 54, pp. 4433-4443. [DOI: https://dx.doi.org/10.1007/s10853-018-3153-z]

10. Soare, V.; Mitrica, D.; Constantin, I.; Popescu, G.; Csaki, I.; Tarcolea, M.; Carcea, I. The Mechanical and Corrosion Behaviors of As-cast and Re-melted AlCrCuFeMnNi Multi-Component High-Entropy Alloy. Metall. Mater. Trans. A Phys. Metall. Mater. Sci.; 2015; 46, pp. 1468-1473. [DOI: https://dx.doi.org/10.1007/s11661-014-2523-7]

11. Pang, J.; Zhang, H.; Zhang, L.; Zhu, Z.; Fu, H.; Li, H.; Wang, A.; Li, Z.; Zhang, H. A ductile Nb₄₀Ti₂₅Al₁₅V₁₀Ta₅Hf₃W₂ refractory high entropy alloy with high specific strength for high-temperature applications. Mater. Sci. Eng. A; 2022; 831, 142290. [DOI: https://dx.doi.org/10.1016/j.msea.2021.142290]

12. Chen, C.; Zhang, H.; Fan, Y.; Zhang, W.; Wei, R.; Wang, T.; Zhang, T.; Li, F. A novel ultrafine-grained high entropy alloy with excellent combination of mechanical and soft magnetic properties. J. Magn. Magn. Mater.; 2020; 502, 166513. [DOI: https://dx.doi.org/10.1016/j.jmmm.2020.166513]

13. Jin, K.; Lu, C.; Wang, L.M.; Qu, J.; Weber, W.J.; Zhang, Y.; Bei, H. Effects of compositional complexity on the ion-irradiation induced swelling and hardening in Ni-containing equiatomic alloys. Scr. Mater.; 2016; 119, pp. 65-70. [DOI: https://dx.doi.org/10.1016/j.scriptamat.2016.03.030]

14. Kumar, N.A.P.K.; Li, C.; Leonard, K.J.; Bei, H.; Zinkle, S.J. Microstructural stability and mechanical behavior of FeNiMnCr high entropy alloy under ion irradiation. Acta Mater.; 2016; 113, pp. 230-244. [DOI: https://dx.doi.org/10.1016/j.actamat.2016.05.007]

15. Egami, T.; Guo, W.; Rack, P.D.; Nagase, T. Irradiation resistance of multicomponent alloys. Metall. Mater. Trans. A Phys. Metall. Mater. Sci.; 2014; 45, pp. 180-183. [DOI: https://dx.doi.org/10.1007/s11661-013-1994-2]

16. Kareer, A.; Waite, J.C.; Li, B.; Couet, A.; Armstrong, D.E.J.; Wilkinson, A.J. Short communication: ‘Low activation, refractory, high entropy alloys for nuclear applications’. J. Nucl. Mater.; 2019; 526, 151744. [DOI: https://dx.doi.org/10.1016/j.jnucmat.2019.151744]

17. Gouda, M.K.; Salman, S.A.; Ebied, S.; Ashmawy, A.M.; Gepreel, M.A.H.; Chiba, A. Biocompatibility and corrosion resistance of low-cost Ti–14Mn–Zr alloys. J. Mater. Res.; 2021; 36, pp. 4883-4893. [DOI: https://dx.doi.org/10.1557/s43578-021-00441-w]

18. Wang, W.; Yang, K.; Wang, Q.; Dai, P.; Fang, H.; Wu, F.; Guo, Q.; Liaw, P.K.; Hua, N. Novel Ti-Zr-Hf-Nb-Fe refractory high-entropy alloys for potential biomedical applications. J. Alloys Compd.; 2022; 906, 164383. [DOI: https://dx.doi.org/10.1016/j.jallcom.2022.164383]

19. Schönecker, S.; Li, X.; Wei, D.; Nozaki, S.; Kato, H.; Vitos, L.; Li, X. Harnessing elastic anisotropy to achieve low-modulus refractory high-entropy alloys for biomedical applications. Mater. Des.; 2022; 215, 110430. [DOI: https://dx.doi.org/10.1016/j.matdes.2022.110430]

20. Yang, W.; Pang, S.; Liu, Y.; Wang, Q.; Liaw, P.K.; Zhang, T. Design and properties of novel Ti–Zr–Hf–Nb–Ta high-entropy alloys for biomedical applications. Intermetallics; 2022; 141, 107421. [DOI: https://dx.doi.org/10.1016/j.intermet.2021.107421]

21. Strozi, R.B.; Leiva, D.R.; Huot, J.; Botta, W.J.; Zepon, G. An approach to design single BCC Mg-containing high entropy alloys for hydrogen storage applications. Int. J. Hydrogen Energy; 2021; 46, pp. 25555-25561. [DOI: https://dx.doi.org/10.1016/j.ijhydene.2021.05.087]

22. Yu, Y.; Xu, N.; Zhu, S.; Qiao, Z.; Zhang, J.; Yang, J.; Liu, W. A novel Cu-doped high entropy alloy with excellent comprehensive performances for marine application. J. Mater. Sci. Technol.; 2021; 69, pp. 48-59. [DOI: https://dx.doi.org/10.1016/j.jmst.2020.08.016]

23. Wani, I.S.; Sathiaraj, G.D.; Ahmed, M.Z.; Reddy, S.R.; Bhattacharjee, P.P. Evolution of microstructure and texture during thermo-mechanical processing of a two phase Al_0.5CoCrFeMnNi high entropy alloy. Mater. Charact.; 2016; 118, pp. 417-424. [DOI: https://dx.doi.org/10.1016/j.matchar.2016.06.021]

24. Wani, I.S.; Bhattacharjee, T.; Sheikh, S.; Bhattacharjee, P.P.; Guo, S.; Tsuji, N. Tailoring nanostructures and mechanical properties of AlCoCrFeNi_2.1 eutectic high entropy alloy using thermo-mechanical processing. Mater. Sci. Eng. A; 2016; 675, pp. 99-109. [DOI: https://dx.doi.org/10.1016/j.msea.2016.08.048]

25. Bhattacharjee, T.; Wani, I.S.; Sheikh, S.; Clark, I.T.; Okawa, T.; Guo, S.; Bhattacharjee, P.P.; Tsuji, N. Simultaneous Strength-Ductility Enhancement of a Nano-Lamellar AlCoCrFeNi_2.1 Eutectic High Entropy Alloy by Cryo-Rolling and Annealing. Sci. Rep.; 2018; 8, 3276. [DOI: https://dx.doi.org/10.1038/s41598-018-21385-y]

26. Deng, Y.; Tasan, C.C.; Pradeep, K.G.; Springer, H.; Kostka, A.; Raabe, D. Design of a twinning-induced plasticity high entropy alloy. Acta Mater.; 2015; 94, pp. 124-133. [DOI: https://dx.doi.org/10.1016/j.actamat.2015.04.014]

27. Yao, M.J.; Pradeep, K.G.; Tasan, C.C.; Raabe, D. A novel, single phase, non-equiatomic FeMnNiCoCr high-entropy alloy with exceptional phase stability and tensile ductility. Scr. Mater.; 2014; 72–73, pp. 5-8. [DOI: https://dx.doi.org/10.1016/j.scriptamat.2013.09.030]

28. Baker, I.; Meng, F. Lamellar coarsening in Fe₂₈Ni₁₈Mn₃₃Al₂₁ and its influence on room temperature tensile behavior. Acta Mater.; 2015; 95, pp. 124-131. [DOI: https://dx.doi.org/10.1016/j.actamat.2015.05.006]

29. Liao, Y.; Baker, I. On the room-temperature deformation mechanisms of lamellar-structured Fe₃₀Ni₂₀Mn₃₅Al₁₅. Mater. Sci. Eng. A; 2011; 528, pp. 3998-4008. [DOI: https://dx.doi.org/10.1016/j.msea.2011.01.089]

30. Stepanov, N.D.; Shaysultanov, D.G.; Chernichenko, R.S.; Tikhonovsky, M.A.; Zherebtsov, S.V. Effect of Al on structure and mechanical properties of Fe–Mn–Cr–Ni–Al non-equiatomic high entropy alloys with high Fe content. J. Alloys Compd.; 2019; 770, pp. 194-203. [DOI: https://dx.doi.org/10.1016/j.jallcom.2018.08.093]

31. Cui, P.; Liu, Y.; Zhou, F.; Lai, Z.; Zhu, J. Enhancing high temperature mechanical properties via modulating B2 phase with Al contents in FeCrNiAlx(x = 0.63,0.71,0.77) high entropy alloys. J. Alloys Compd.; 2022; 903, 163883. [DOI: https://dx.doi.org/10.1016/j.jallcom.2022.163883]

32. Kishore, K.; Chandan, A.K.; Hung, P.T.; Kumar, S.; Kawasaki, M.; Gubicza, J. On the enhanced hardening ability and plasticity mechanisms in a novel Mn-added CoCrNi medium entropy alloy during high-pressure torsion. J. Alloys Compd.; 2022; 904, 163941. [DOI: https://dx.doi.org/10.1016/j.jallcom.2022.163941]

33. Oh, M.C.; Sharma, A.; Lee, H.; Ahn, B. Phase separation and mechanical behavior of AlCoCrFeNi-X (X = Cu, Mn, Ti) high entropy alloys processed via powder metallurgy. Intermetallics; 2021; 139, 107369. [DOI: https://dx.doi.org/10.1016/j.intermet.2021.107369]

34. Chen, C.; Wang, W.; Li, H.; Wei, P.; Zhang, W.; Fan, Y.; Chen, J.; Yuan, S.; Wei, R.; Zhang, T. et al. Effects of Al and Mn on microstructure, magnetic and mechanical properties of Fe₄₀Co₄₀Ni₁₀M₁₀ (M=Al, Mn) medium entropy alloys. J. Alloys Compd.; 2022; 890, 161779. [DOI: https://dx.doi.org/10.1016/j.jallcom.2021.161779]

35. Meng, F.; Qiu, J.; Baker, I. The effects of chromium on the microstructure and tensile behavior of Fe₃₀Ni₂₀Mn₃₅Al₁₅. Mater. Sci. Eng. A; 2013; 586, pp. 45-52. [DOI: https://dx.doi.org/10.1016/j.msea.2013.08.005]

36. Gu, X.; Zhuang, Y.; Jia, P. Evolution of the microstructure and mechanical properties of as-cast Al_0.3CoCrFeNi high entropy alloys by adding Si content. Mater. Sci. Eng. A; 2022; 840, 142983. [DOI: https://dx.doi.org/10.1016/j.msea.2022.142983]

37. Guo, Y.; He, J.; Li, Z.; Jia, L.; Wu, X.; Liu, C. Strengthening and dynamic recrystallization mediated by Si-alloying in a refractory high entropy alloy. Mater. Sci. Eng. A; 2022; 832, 142480. [DOI: https://dx.doi.org/10.1016/j.msea.2021.142480]

38. Xu, Z.Q.; Ma, Z.L.; Tan, Y.; Wang, M.; Zhao, Y.; Cheng, X.W. Effects of Si additions on microstructures and mechanical properties of VNbTiTaSix refractory high-entropy alloys. J. Alloys Compd.; 2022; 900, 163517. [DOI: https://dx.doi.org/10.1016/j.jallcom.2021.163517]

39. Liu, H.; Sun, S.; Zhang, T.; Zhang, G.; Yang, H.; Hao, J. Effect of Si addition on microstructure and wear behavior of AlCoCrFeNi high-entropy alloy coatings prepared by laser cladding. Surf. Coat. Technol.; 2021; 405, 126522. [DOI: https://dx.doi.org/10.1016/j.surfcoat.2020.126522]

40. Ma, M.; Han, A.; Zhang, Z.; Lian, Y.; Zhao, C.; Zhang, J. The role of Si on microstructure and high-temperature oxidation of CoCr2FeNb0.5Ni high-entropy alloy coating. Corros. Sci.; 2021; 185, 109417. [DOI: https://dx.doi.org/10.1016/j.corsci.2021.109417]

41. Huang, L.; Wang, X.; Jia, F.; Zhao, X.; Huang, B.; Ma, J.; Wang, C. Effect of Si element on phase transformation and mechanical properties for FeCoCrNiSix high entropy alloys. Mater. Lett.; 2021; 282, 128809. [DOI: https://dx.doi.org/10.1016/j.matlet.2020.128809]

42. Hou, Y.; Liu, T.; He, D.; Li, Z.; Chen, L.; Su, H.; Fu, P.; Dai, P.; Huang, W. Sustaining strength-ductility synergy of SLM Fe₅₀Mn₃₀Co₁₀Cr₁₀ metastable high-entropy alloy by Si addition. Intermetallics; 2022; 145, 107565. [DOI: https://dx.doi.org/10.1016/j.intermet.2022.107565]

43. Guo, R.; Pan, J.; Liu, L. Achieving dual-phase structure and improved mechanical properties in AlCoCrFeTi_0.5 high-entropy alloys by addition of Ni. Mater. Sci. Eng. A; 2022; 831, 142194. [DOI: https://dx.doi.org/10.1016/j.msea.2021.142194]

44. Qiu, H.; Zhu, H.; Zhang, J.; Xie, Z. Effect of Fe content upon the microstructures and mechanical properties of FexCoNiCu high entropy alloys. Mater. Sci. Eng. A; 2020; 769, 138514. [DOI: https://dx.doi.org/10.1016/j.msea.2019.138514]

45. Huang, Y.; Gao, J.; Wang, S.; Guan, D.; Xu, Y.; Hu, X.; Rainforth, W.M.; Zhu, Q.; Todd, I. Influence of tantalum composition on mechanical behavior and deformation mechanisms of TiZrHfTax high entropy alloys. J. Alloys Compd.; 2022; 903, 163796. [DOI: https://dx.doi.org/10.1016/j.jallcom.2022.163796]

46. Li, X.; Gao, X.; Lu, H.; Shi, C.; Guo, N.; Yin, F. Microstructure evolution and mechanical properties of AlCrFe₂Ni₂(MoNb)_x high entropy alloys. J. Mater. Res. Technol.; 2022; 17, pp. 865-875. [DOI: https://dx.doi.org/10.1016/j.jmrt.2022.01.055]

47. Wu, Y.; Zhang, Y. Design and High-Throughput Screening of High Entropy Alloys. Advances in High-Entropy Alloys-Materials Research, Exotic Properties and Applications; IntechOpen: London, UK, 2021; pp. 1-16. [DOI: https://dx.doi.org/10.5772/intechopen.96714]

48. Kurz, W.; Bezençon, C.; Gäumann, M. Columnar to equiaxed transition in solidification processing. Sci. Technol. Adv. Mater.; 2001; 2, pp. 185-191. [DOI: https://dx.doi.org/10.1016/S1468-6996(01)00047-X]

49. Singh, S.; Wanderka, N.; Murty, B.S.; Glatzel, U.; Banhart, J. Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy. Acta Mater.; 2011; 59, pp. 182-190. [DOI: https://dx.doi.org/10.1016/j.actamat.2010.09.023]

50. Ghaderi, A.; Moghanni, H.; Dehghani, K. Microstructural Evolution and Mechanical Properties of Al_0.5CoCrFeNi High-Entropy Alloy after Cold Rolling and Annealing Treatments. J. Mater. Eng. Perform.; 2021; 30, pp. 7817-7825. [DOI: https://dx.doi.org/10.1007/s11665-021-05886-y]