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Review

Additive Manufacturing Technologies of High Entropy Alloys (HEA): Review and Prospects

by
Tomer Ron
*,
Amnon Shirizly
and
Eli Aghion
*
Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
*
Authors to whom correspondence should be addressed.
Materials 2023, 16(6), 2454; https://doi.org/10.3390/ma16062454
Submission received: 12 February 2023 / Revised: 14 March 2023 / Accepted: 17 March 2023 / Published: 19 March 2023
(This article belongs to the Section Metals and Alloys)
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Abstract

:
Additive manufacturing (AM) technologies have gained considerable attention in recent years as an innovative method to produce high entropy alloy (HEA) components. The unique and excellent mechanical and environmental properties of HEAs can be used in various demanding applications, such as the aerospace and automotive industries. This review paper aims to inspect the status and prospects of research and development related to the production of HEAs by AM technologies. Several AM processes can be used to fabricate HEA components, mainly powder bed fusion (PBF), direct energy deposition (DED), material extrusion (ME), and binder jetting (BJ). PBF technologies, such as selective laser melting (SLM) and electron beam melting (EBM), have been widely used to produce HEA components with good dimensional accuracy and surface finish. DED techniques, such as blown powder deposition (BPD) and wire arc AM (WAAM), that have high deposition rates can be used to produce large, custom-made parts with relatively reduced surface finish quality. BJ and ME techniques can be used to produce green bodies that require subsequent sintering to obtain adequate density. The use of AM to produce HEA components provides the ability to make complex shapes and create composite materials with reinforced particles. However, the microstructure and mechanical properties of AM-produced HEAs can be significantly affected by the processing parameters and post-processing heat treatment, but overall, AM technology appears to be a promising approach for producing advanced HEA components with unique properties. This paper reviews the various technologies and associated aspects of AM for HEAs. The concluding remarks highlight the critical effect of the printing parameters in relation to the complex synthesis mechanism of HEA elements that is required to obtain adequate properties. In addition, the importance of using feedstock material in the form of mix elemental powder or wires rather than pre-alloyed substance is also emphasized in order that HEA components can be produced by AM processes at an affordable cost.

1. Introduction

High entropy alloys (HEAs) offer unique properties, such as high-temperature stability, enhanced specific strength, wear resistance, and excellent corrosion performance in harsh environments. Unlike conventional alloys that typically contain one major element and a small number of alloying elements, HEAs are multi-component systems comprising a few principal elements, as illustrated in Figure 1. They are typically composed of at least five elements, each with individual atomic concentrations ranging from 5−35%. The ability of HEAs to form solid phase solutions is largely due to their configurational entropy and the ability to be synthesized effectively [1,2,3].
The development of HEAs is based on thermodynamic considerations that aim to minimize the Gibbs free energy. This is mainly related to two dominating parameters [4]: (1) the differences in atomic size ( δ ); and (2) the mix enthalpy ( ∆ H m i x ), as shown by the following equations (for a binary system):
δ = ∑ i = 1 , j ≠ 1 N C i ( 1 − r i / ( ∑ i = 1 N c i r i ) ) 2  
Δ H m i x = ∑ i = 1 , j ≠ 1 N 4 H A B m i x c i
where r i is the atomic radius of element i, H A B m i x is the mix enthalpy, and c i and c j are the atomic concentrations of elements i and j, respectively. It should be pointed out that the main parameter that will determine the stability of the material system is the free energy of the mixed phases ( ∆ G m i x = ∆ H m i x − T ∆ S m i x ). This parameter is closely correlated with the dimension of Ω as defined by the following Equation (3) [4]:
Ω = T m ⋅ Δ S m i x | Δ H m i x |
where T m is the average melting temperature of the elemental ingredients, ∆ S m i x is the mixed entropy, and ∆ H m i x is the mixed enthalpy.
HEAs can be conventionally produced using various methods, such as the arc melting furnace (AMF) [5,6,7], mechanical alloying [8], plasma spark sintering [9], and physical vapor deposition [10]. Lately, there has been considerable interest in producing these alloys by AM technologies, which enable the production of complex components with a minimal amount of post-processing steps.
AM involves building a part layer by layer. As such, most relevant AM technologies commonly use a focused heat source to melt a feedstock material, such as powder or wire, which is then consolidated in subsequent cooling to form a part. AM has gained much attention in recent years due to its unique design capabilities and short lead times. According to ASTM F2792—12a, there are seven main categories of AM processes, as shown in Figure 2. These processes can be divided into three groups: (i) binder-based AM, including binder jetting (BJ) and material extrusion (ME); (ii) high energy heat source AM, including direct energy deposition (DED), powder bed fusion (PBF), and sheet lamination; and (iii) liquid-based AM, including material jetting and vat photopolymerization. Metallic parts can be fabricated using binder-based and high energy heat source technologies.

2. Additive Manufacturing (AM) Technologies of High Entropy Alloys (HEAs)

The use of AM technologies to produce HEAs has gained increasing attention in recent years. Various review papers have been published on this topic, focusing on the corrosion performance, powder manufacturing, specific HEA compositions, specific AM technologies and typical microstructures of HEAs produced using AM [11,12,13,14,15,16,17,18,19,20,21]. It is well known that optimizing the processing parameters can improve the mechanical properties of AM-produced HEAs, including refining the microstructure and enhancing properties through post-processing heat treatment [11]. However, synthesizing HEAs such as CrFeCoNi and CrMnFeCoNi HEAs by AM using mixed elemental powder remains challenging due to issues such as elemental segregation and the different melting points of the elements [12]. Imperfections of the AM-produced HEAs such as volume defects along the build direction and elemental segregation can serve as corrosion initiation sites and reduce corrosion resistance. However, controlling the printing parameters can minimize volume defects, and suitable heat treatment can control elemental segregation [19]. The use of selective laser melting (SLM) can improve the microstructure and mechanical strength, but defects such as cracks and porosity may still be present. To date, most research has focused on CrMnFeCoNi and AlCrFeCoNi alloys, but there remains a need for further research on lightweight HEAs [15]. This review aims to provide an overview of the various AM technologies and underline the differences between them in terms of their effects on the microstructure and mechanical properties of HEAs. The rapidly growing number of publications on the topic highlights the need for regular updates on the latest developments in the field.
The concept of using AM technologies to fabricate HEA components was first introduced by Kunce et al. in 2013 [22]. Since then, an increasingly large number of publications on the AM of HEAs have been published, as shown in Figure 3. This figure is based on the data collected for this review, and clearly indicates the intense interest in using AM to produce HEA components.
Research studies on the AM of HEAs can be broadly classified into four main process technologies: (i) PBF, in which a powder is spread on a printing tray and selectively melted by an energy source, such as a laser beam [23,24,25,26], an electron beam [27], or arc melting [28]; (ii) DED, in which the metal raw material is directly melted layer by layer using different energy sources, such as a laser beam, an electron beam, or arc melting, and the feedstock material can be in the form of powder (using blown powder deposition (BPD) technology [29,30]) or in the form of wire (using arc and laser melting as the heat source—that are usually known as wire arc AM (WAAM) [31,32,33,34] and wire laser AM (WLAM) [35,36]); (iii) BJ, where the powder bed technology uses a liquid binder instead of a heat source, and consequently the printed part is in the form of a green body that requires sintering to obtain adequate density [37,38]; and (iv) ME, where the mixture of powder and binder is extruded through a nozzle to fabricate layer by layer (in this case the printed part is also a green body that requires sintering [39,40]).
The selection of alloying elements for HEAs is complex and depends on various thermodynamic factors to obtain desired single phase material, as well as adequate properties and affordable cost. The most common alloying elements are transition metals, such as Cr, Fe, Co, and Ni along with Al, Mn, and Ti, as illustrated in Figure 4. Another group of HEAs produced by AM technologies includes common refractory metals, such as Nb, Mo, Ta, and W.

2.1. Raw Materials

The synthesis of HEAs involves combining different alloying elements to form a solid solution structure. Conventionally, HEAs are synthesized using an AMF that produces an irregular shape that can be subsequently machined. For most AM technologies, the feedstock material is in the form of powder. In practice, there are two types of powder that can be used. The first type is a pre-alloyed powder, which is synthesized by AMF and produced by gas atomization, hydrogenation, plasma spheroidization, or vacuum electron beam melting [41]. The second type is a mix elemental powder, which is composed of a mixture of the constituent elements. Around 60% of published studies discuss pre-alloyed powder as the feedstock material, as shown in Figure 5. In some research, the authors have modified the composition of a single element to investigate its effect on microstructure formation by a blended powder of pre-alloyed powder with another pure element. In addition, wire can be used as the raw material for DED technology. In this case, pre-alloyed wire can be used, or a combination of three or more commercial wires can be employed.

2.2. Powder Bed Fusion (PBF)

In PBF technologies, an energy source, such as a laser, an electron beam, or an electric or plasma arc is used to scan each layer of powder. The energy in the beam selectively melts the powder according to the computer-aided design (CAD) model of the part. After one layer has been scanned, the piston of the building chamber moves downward, and another layer of powder is applied. A schematic illustration of the PBF process is shown in Figure 6. An inert atmosphere or vacuum environment is necessary to provide a shielding atmosphere for the molten metal. The main processing parameters in the PBF process are energy/power, scan velocity, layer thickness, and hatch spacing. PBF is known as one of the most accurate AM technologies, allowing the production of complex-geometry parts with a relatively superior surface finish [42,43].

2.2.1. Laser-Based PBF (L-PBF)

PBF, also known as SLM, selective laser sintering (SLS), or direct metal laser sintering (DMLS) [44], is the most common AM method [45]. It uses a laser beam as a power source to selectively melt metallic powder in an inert gas atmosphere, usually argon or nitrogen. L-PBF has the fastest cooling rate of all AM technologies [46], which leads to rapid solidification and fine grain size microstructure that can prevent undesired element segregation, especially in multicomponent systems. However, the rapid cooling rate also creates high residual stress due to the formation of complex dislocation networks during the shrinkage of the melt pool. This can sometimes make it difficult to produce crack-free parts and may necessitate subsequent annealing treatment.
Lin et al. studied the effect of annealing on the mechanical properties of FeCoCrNi HEAs. They found that annealing at 900 °C decomposed the dislocation network, leading to a reduction in residual stress. Higher annealing temperatures of 1100 °C resulted in a further reduction in residual stress and the formation of grains rich in twins through a recrystallization process [47]. Hen et al. discovered that annealing of AlCrFe2Ni2 led to a reduction in ultimate tensile strength (UTS), while significantly increasing the elongation. The heat treatment caused segregation, leading to the formation of an additional FCC phase. The amount of FCC phase increased with higher heat treatment temperatures [48].
The annealing environment also affects the properties of HEAs. Tong et al. investigated the oxidation behavior of CrMnFeCoNi HEAs at high temperatures and found that heat treatment in an ambient atmosphere led to the formation of an oxide layer on the external surface. The thickness of the oxide layer and the irregularity of its morphology increased with temperature [49].
Many studies on the production of HEAs using L-PBF have utilized pre-alloy powders. Those data are presented in Table 1, along with the obtained crystal structure. These powders were commercially produced by a gas atomization process.
Blended powders that consist of pre-alloyed HEA powder mixed with a pure element were also studied in order to evaluate the effect of the additional element on the microstructure and phase composition, as described in Table 2. For example, Sun et al. explored the effect of different Al concentrations (X = 0, 0.1, 0.5, 1) on the microstructure of an AlXCrFeCoNi system. They revealed that the Al content was able to change the microstructure from FCC (for X = 0, 0.1) to FCC + BCC/B2 (for X = 0.5) and BCC/B2 (for X = 1) and found that the formation of the dual phase FCC + BCC/B2 in Al0.5CrFeCoNi reduced the crack density [72]. Another example is found in the study by Su et al, on the addition of Al (X = 0, 0.5, 0.75, 1) to an AlXCrFeNi2Cu system. Apparently, the CrFeNi2Cu HEA produced by the L-PBF process has a columnar FCC face microstructure that was prone to hot cracks. The addition of Al (X = 0.75) formed a cellular FCC dendrite with a B2 face matrix that reduced crack propagation [102].

2.2.2. Electron Beam-Based PBF (EB-PBF)

EB-PBF is a technology that uses an electron beam as the energy source to selectively melt metallic powder. It is also known as electron beam melting (EBM) or selective electron beam melting (SEBM). The electron beam process usually requires a high vacuum environment. Like other PBF technologies, optimization of the printing parameters is necessary to obtain high-density samples. The main printing parameters include electron beam current, scanning speed, layer thickness, and hatch spacing. Before the powder is selectively melted by the electron beam, a pre-heating process (up to 1100 °C) is performed using a defocused electron beam to scan the entire powder surface. This pre-heating process is designed to prevent powder spattering during melting by the electron beam and to reduce residual stresses [110]. However, the pre-heating process is a heat treatment, and the properties of the metal can be affected by the duration of this process. Since the AM process takes time, the lower section of the AM parts may be more affected by this heat treatment.
The first attempt to use EB-PBF to produce a HEA was performed by Fujieda et al. in 2015 [111]. This was related to an AlCrFeCoNi HEA that was produced by SEBM and resulted in the formation of a two-phase structure. This research was later followed by another 11 studies that also used EB-PBF to manufacture various HEAs, as presented in Table 3. The EB-PBF of AlCrFeCoNi was also studied by Shiratori et al. [112] and Yamanaka et al. [110], with both studies observing different microstructures at the bottom and top sections of the printed parts. The AlCrFeCoNi produced by AMF had a BCC/B2 structure, but the pre-heating process during EB-PBF exposed the part to high temperatures, causing element segregation and the formation of a FCC phase at grain boundaries. As a result, the bottom section, which was exposed to the heat treatment for a longer period, had a higher fraction of the FCC phase than the top part. Similar phenomena were also observed in the preheating of AlFeCoNiCu by Zhang et al. [113], as illustrated schematically in Figure 7.

2.2.3. Mix Elemental Powder as Feedstock Material for PBF Technology

The use of mixed elemental powder in PBF processes is relatively undeveloped, with only 14% of published studies dealing with this approach. This is mainly related to the inherent limitation of using this feedstock material in terms of adequate synthesis of HEAs. However, there are major advantages in using mix elemental powders for manufacturing HEAs. These include more flexibility in composition, lower powder manufacturing costs, and the relatively vast availability of commercial powders [119]. Table 4 presents a list of HEAs that were fabricated using mix elemental powders as feedstock material in PBF processes.
Hou et al. [120] studied the effect of laser energy density on the as-built density of a CrFeCoNi HEA using both mix elemental and pre-alloyed powders, as shown in Figure 8. They found that a higher laser energy density was needed to fabricate the parts from mix elemental powder due to the in situ formation of the HEA. Additionally, they found that under the same printing conditions (apart from the laser power), the density of the pre-alloyed powder samples was higher compared to that of the mix elemental powder samples. Other attempts to produce HEAs using mix elemental powder were carried out by Zhang et al. [121], Huber et al. [122], and Ron et. al. [123] on different alloys having the composition of NbMoTaW and VNbMoTaW. High relative density can be achieved by optimization of the printing parameters. VNbMoTaW HEA produced using L-PBF is shown in Figure 9 and demonstrates an increase from 38% relative density in the initial production attempts to 95% relative density in the advanced attempts. The general insights of those studies were basically in line with those of Hou et al.
Table
Table 4. Production of HEAs by PBF process using mix elemental powder as feedstock material.
Table 4. Production of HEAs by PBF process using mix elemental powder as feedstock material.
AlloyAM SystemCrystal StructureRef.
Al0.4CrFeCoNiPlasma arcFCC[124]
AlCrFeCoNi2.1Electric arcFCC + BCC[28]
Al0.5CrNbMoTa0.5EB-PBFBCC + FCC [125]
Al0.5CrNbMoTa0.5EB-PBFBCC + FCC[126]
CrFeCoNiLPBFFCC[120,127]
CrMnFeCoNiLPBFFCC[119]
CrMnFeCoNiElectric arcFCC[128]
NbMoTaWLPBFBCC[121]
NiNbMoTaLPBFBCC[129]
Ti0.5Ni0.5NbMoTaLPBFBCC[129]
TiNbMoTaLPBFBCC[129]
TiVCrFeNiElectric arcFCC[130]
VNbMoTaWLPBFBCC[122,123]

2.3. Direct Energy Deposition (DED)

DED is an AM process in which a high energy source, such as a laser beam or plasma arc, is used to melt and deposit material onto a substrate [131]. The feedstock material, which can be either mix elemental powder or pre-alloyed powder, is melted and fused to the previous layer to create metallurgical bonds between layers. The DED process has a higher deposition rate than PBF technologies and is mostly not limited by the size of the printing chamber. However, the surface roughness of DED-produced parts is generally lower and the complexity of parts that can be produced is limited compared to PBF systems [132]. The main processing parameters of the DED process are energy/power, scan velocity, layer thickness, hatch spacing, and material feed rate. These parameters must be carefully controlled to achieve the desired properties.

2.3.1. Blown Powder Deposition (BPD)

Blown powder deposition (BPD) is an AM process that involves directing a laser or plasma beam at metal powder that has been suspended in a high-velocity gas stream. This generates a melt pool from which the part is built up layer by layer, according to a CAD model [133]. BPD is also known as laser metal deposition (LMD), laser powder deposition (LPD), or laser engineered net shape (LENS). A schematic illustration of the BPD process along with the feeding system is shown in Figure 10. A large number of studies using mix elemental powder and pre-alloyed powder to produce HEAs via BPD processes by laser and arc beam energy have been published, as shown in Table 5.
In general, DED technology is known for its high deposition rate, which results in a large number of thermal cycles during the manufacturing process. These thermal cycles can affect the microstructure of the printed parts in various regions. Usually, the top region will retain a fine grain size with high dislocation density, while the bottom region will exhibit a large grain size with low dislocation density. This phenomenon is strongly related to the high number of heat treatment cycles, which is similar to annealing treatment [134]. A schematic illustration of this phenomenon as a function of its printing orientation is shown in Figure 11.
In addition, the heat treatment during the DED process can cause segregation, especially with increased production time. For certain compositions of HEA, such as AlCrFeCoNi, this segregation can lead to significant changes in the microstructure between the bottom and top of the printed part. For example, new FCC phases can be generated in addition to the BCC phase matrix obtained during rapid solidification [135], or alternatively, the fraction of the second phase may increase [136].
The feedstock material used in the DED process, and in particular the type of powder, can also affect the formation of new phases. In the case of a AlCrFeCoNi HEA using pre-alloyed powder [137,138,139], a single solid solution part with BCC/B2 structure is obtained. However, when mix elemental powder is used [140,141,142], the resulting part has a dual FCC + BCC/B2 structure. This can mainly be related to the easier segregation capability in the case of mix elemental powders.
Table
Table 5. HEAs produced by BPD process as part of direct metal deposition (DMD) technology.
Table 5. HEAs produced by BPD process as part of direct metal deposition (DMD) technology.
AlloyAM SystemFeedstock MaterialCrystal StructureRef.
Al0.25FeCoNiCuLaserElemental FCC[143]
Al0.3CrFeCoNiLaserPre-alloyedFCC[144,145,146,147,148]
Al0.3CrFeCoNiLaserElemental FCC[149]
Al0.4CrFeCoNiLaserElemental FCC[140]
Al0.4CrFeCoNiPlasma arcElemental FCC[150]
Al0.4CrFeCoNiPlasma arcElemental FCC + BCC/B2 + σ[151,152]
Al0.6CrFeCoNiLaserElemental FCC + BCC/B2[149]
Al0.6CrFeCoNiLaserPre-alloyed FCC + BCC/B2[148,149]
Al0.7CrFeCoNiLaserElemental FCC + BCC/B2[140]
Al0.85CrFeCoNiLaserPre-alloyed BCC/B2[148,149]
Al0.85CrFeCoNiLaserElemental BCC/B2[149]
AlCrFeCoNiLaserPre-alloyedBCC/B2[135,137,138,139]
AlCrFeCoNiLaserElemental FCC + BCC/B2[140,141,142]
Al0.3CrFeCoNi1.7LaserElemental FCC[142]
Al0.7CrFeCoNi1.3LaserElemental FCC + BCC/B2[142]
Al1.7CrFeCoNi0.3LaserElemental BCC/B2[142]
Al0.6Cr0.3Fe0.3CoNiLaserElemental FCC + BCC/B2[136]
Al0.6CrFeCoNi2.1LaserPre-alloyed +AlFCC + BCC/B2[148,153]
Al0.7CrFeCoNi2.1LaserPre-alloyed +AlFCC + BCC/B2[153]
Al0.85CrFeCoNi2.1LaserPre-alloyed +AlBCC/B2[153]
AlCrFeCoNi2.1LaserPre-alloyed +AlFCC + BCC/B2[153]
Al1.1CrFeCoNi2.1LaserPre-alloyed +AlFCC + BCC/B2[153]
Al1.2CrFeCoNi2.1Plasma arcElemental FCC + BCC/B2[154]
AlCrFeCoNi2.1LaserPre-alloyedFCC + BCC/B2[155,156]
AlCrFeCoNi2.1Plasma arcElemental FCC + BCC/B2 + σ[157]
AlCrFeCoNi2.1LaserElemental FCC + BCC/B2[158]
AlV0.3CrFeMoLaserElemental BCC[159]
AlV7.5CrFeMoLaserElemental BCC[159]
AlV10CrFeMoLaserElemental BCC[159]
AlV18.5CrFeMoLaserElemental BCC[159]
Al2CrMnFeCoNiLaserPre-alloyed + AlFCC[160]
Al5CrMnFeCoNiLaserPre-alloyed + AlFCC + BCC[160]
Al8CrMnFeCoNiLaserPre-alloyed + AlFCC + BCC[160]
Al0.5FeCoNiCuLaserElemental FCC[143]
Al0.75FeCoNiCuLaserElemental FCC + BCC[143]
AlCrFeNiCuLaserElemental FCC + BCC[161]
AlTiCrFeCoNiLaserPre-alloyedFCC + BCC[162]
Al0.3Ti0.2Cr0.7FeCoNi1.7LaserPre-alloyedFCC + L1[163]
AlTiCrFeCoNiLaserPre-alloyedFCC + BCC + AlNi3[164,165]
AlTiCrFeCoNiLaserElementalFCC + BCC + AlNi3[166]
AlCrFeCoNiCuLaserPre-alloyedFCC + BCC[164,165]
Al0.17Ti0.08CrFeCoNiLaserPre-alloyedFCC[167]
AlCrFeCoNiCuLaserElementalFCC + BCC[166]
CrMnFeCoNiLaserPre-alloyedFCC[134,160,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182]
CrMnFeCoNiLaserElementalFCC[183]
CrFeCoNiLaserPre-alloyedFCC[139]
CrFeCoNiLaserPre-alloyedFCC + µ + σ[184]
CrFeCoNiLaserElemental FCC + Co7Fe3[185]
CrFeCoNiPlasma arcElemental FCC[151,152,186]
CrFeCoNiMoLaserPre-alloyedFCC[187]
CrFeCoNiNbLaserElemental FCC + Laves + MC[188]
CrFeCoNiNb0.4Plasma arcElemental FCC + Laves[151,152]
CrFeCoNiTa0.4Plasma arcElemental FCC + Laves[151,152]
CrFeCoNiW0.2Plasma arcElemental FCC + μ[186]
CrFeCoNiW0.5Plasma arcElemental FCC + μ[186]
CrFeCoNiW0.24Plasma arcElemental FCC + BCC + μ[186]
CrFeCoNiWPlasma arcElemental FCC + BCC + μ[186]
CrFeCoNi0.1Ta0.2Plasma arcElemental FCC + Fe7(NbTa)3[189]
CrFeCoNi0.3Ta0.2Plasma arcElemental FCC + Fe7(NbTa)3[189]
CrFeCoNi0.5Ta0.2Plasma arcElemental FCC + Fe7(NbTa)3[189]
CrFeCoNiTa0.4Plasma arcElemental FCC + Co2Ta[189]
Ti0.6CrMnFeCoNiLaserPre-alloyedFCC + BCC[182]
TiCrMnFeCoNiLaserPre-alloyedFCC + BCC + σ[182]
TiCrFeCoNiLaserElemental FCC + σ + δ + Ni3Ti2[190]
TiVCrFeNiZrLaserElemental C14-Laves + α-Ti[22]
TiVZrNbMoLaserElemental BCC+NbTi4 + α-Zr[191]
TiZrNbHfTaLaserElemental BCC[192]
TiZrNbTaLaserElemental BCC[193]
NbMoTaWLaserElemental BCC[194,195,196]
VNbMoTaWLaserElemental BCC[197]

2.3.2. Wire Deposition

Wire deposition, also known as wire arc AM (WAAM), wire laser AM (WLAM), or wire electron beam AM (WEAM), is a DED process that uses welding wire as the raw material. It has gained increased attention in recent years due to its potential for producing large, customized, near-net-shape metal components at a relatively reduced cost. This process involves using TIG welding, MIG welding, plasma torches, laser beams, or electron beams to deposit sequential layers of material from a wire feedstock without the need for extra tooling [198,199]. A schematic illustration of a typical WAAM technology process is shown in Figure 12.
The manufacturing of HEAs using wires as the raw material has been demonstrated by several studies, as shown in Table 6, and has been performed by using a number of commercial welding wires or by fabricating a pre-alloyed welding wire. However, the fabrication of pre-alloyed wires is significantly more expensive than the other options is and quite complex in terms of wire preparation. According to Ahsan et al. [200], the complex process is carried out as follows: (i) melting the HEA elements in an induction furnace; (ii) casting in a cylindrical ingot; (iii) hot isostatic press (HIP) treatment; (iv) machining and extrusion; and (v) wire drawing to construct a 1.2 mm welding wire. To avoid the complexity of fabricating pre-alloyed wires, it is possible to use combined cable wires (CCWs), which consist of 3–7 thin commercial wires, as illustrated in Figure 13. It should be pointed out that the chemical composition of the final HEA depends on the possible combinations of commercial wires; hence, in practice, not every composition is possible. According to Shen et al. [201], the AM HEA produced using wire DED with seven different wires (one Fe wires, two Ni wires, two Al wires, one Co wire and one 304 stainless steel wire) had similar mechanical properties to those of the cast alloy made with the same wires as feedstock material for the AMF process. Other studies [202,203] have demonstrated that the use of three non-pure welding wires can form a single solid solution, as shown in Figure 14.

2.4. Binder Jetting (BJ)

BJ is a low-cost AM process that uses a liquid binder to bond powder particles together in order to form a green body that should then be sintered [211]. The powder is spread layer by layer and the binder is applied using an inkjet printing head according to the CAD design. BJ is a unique process that does not use a heat source, and hence the use of pre-alloyed powder as feedstock material is a precondition, as demonstrated by the various studies presented in Table 7. A schematic illustration of the BJ technology process is shown in Figure 15. The main processing parameters in BJ technology relate to the layer thickness, the size and number of the inkjet nozzles, the powder bed temperature, and the printing speed. In addition, the post-processing parameters, which relate to the sintering process, are the sintering temperature and duration.
It has been shown that it is possible to produce HEA components by BJ and sintering; however, there are a few challenges to be addressed. Elevated sintering temperatures reduce the amount of porosity, but also increase shrinkage. In addition, the sintering process, like any other heat treatment, can modify the microstructure and induce the formation of secondary phases. For example, Karlsson et al. found that the sintering of a AlCrFeCoNi HEA at a relatively low temperature (900 °C) resulted in the formation of an undesired sigma phase in addition to the FCC and BCC/B2 phases. In parallel, sintering at high temperatures (above 1200 °C) resulted in the formation of a single BCC phase [212].

2.5. Material Extrusion (ME)

ME is an AM process that uses extrusion to produce components from a soft, malleable, raw material. This process is typically used for producing polymer parts, but it can also be used to produce metallic parts. The feedstock material for metallic parts consists of a mixture of metallic powder and a thermoplastic binder. The feedstock material is fed through a nozzle layer by layer according to a CAD model. There are three options for loading the feedstock material [214]: (i) extruding a rod made from metallic powder and thermoplastic binder using a plunger; (ii) extruding filaments, typically made of polymers; or (iii) extruding a metallic powder and binder using a screw extruder where the rotating screw is able to pump and push the feeding material through a nozzle and toward the printing tray. Following the printing process, a sintering process is required to transform the green body into a high-density metal part. A schematic illustration of the ME process using a plunger is shown in Figure 16. Table 8 introduces a couple of HEAs produced by ME technology using mix elemental powder and pre-alloy as the feedstock material.

2.6. Composite Materials

Composite materials with a HEA matrix can easily be created using AM processes that involve powder. These materials can be reinforced with dispersion particles or have a laminated structure. Metal carbides, nitrides, borides, and oxides can be used as reinforcing particles in composite materials with metal alloy matrices [217]. Table 9 introduces different composite materials with a pre-alloyed HEA matrix. An example of a reinforced HEA using TiC nano-ceramic particles demonstrated by Chen et al. [218] showed improved mechanical properties, such as strength and ductility. In this case, the nano-particle reinforcement also enhanced work hardening and grain refinement. Another option for a metal matrix composite is to add refractory elements with a high melting temperature, such as W, as reinforcing particles [219]. BPD systems with two different powder feedstocks can also be used to produce a metal matrix composite by depositing a laminated structure from two different HEAs [220].

2.7. Interstitial Doping

Interstitial doping relates to the possibility of adding a small number of interstitial atoms, such as carbon, nitrogen, and oxygen, that can increase the strength of HEAs without decreasing their ductility. For example, the addition of carbon to a FeCoCrNiMn HEA has been shown to increase both strength and ductility [234]. This was due to the modification of the deformation mechanism from relatively pure dislocation glide to combined dislocation glide and twinning. The addition of oxygen to a TiZrHfNb HEA can also enhance strain hardening by creating complexes that promote double cross-slip and the formation of Frank–Read sources that enhance dislocation multiplication [235]. Similarly, the doping of nitrogen into a FeCoNiCr HEA can also increase both strength and ductility by forming low angle boundaries and increasing dislocation networks [236]. Table 10 introduces several examples of HEA systems that incorporate interstitial doping using a L-PBF process and pre-alloyed feedstock material.

2.8. Effect of Printing Parameter

To obtain high-density HEA parts of by AM, careful optimization of the printing parameters is required. Inadequate parameters can result in the production of inherent defects. For example, excessively high energy density can cause over-melting and vaporization within the melt pool, while insufficient energy density can lead to incomplete fusion of melt pools. Table 11 presents the printing parameters used for some common HEA compositions in various AM processes. In general, increasing the energy density increases the density until reaching optimal printing parameters, beyond which the relative density may decrease due to increased defects from vaporization and splashing of the melt pool. However, increasing the energy density can improve surface finish [75] and increase the lattice parameter [173]. The applied energy density also affects the microstructure; for example, relatively low energy density can result in cellular microstructures, while high energy density can produce lamellar structures due to the higher cooling rates [56]. The microstructure of HEA produced by the DED process can be affected by the printing time, where the lower section of the part undergoes more thermal cycles. Xiang et al. [172] showed that the printing parameters can affect this phenomenon. For example, relatively low energy density can result in a columnar structure in the lower and middle sections, with a mixed columnar and equiaxed grain structure in the top part. In parallel, relatively high energy density can result in an equiaxed grain structure throughout the alloy. The optimal energy density depends on the feedstock material used. The effect of volume energy density (VED) on relative density has been investigated by Farquhar et al. [101], as shown in Figure 17. CrFeCoNi pre-alloyed powder was mixed with Cu powder and Ti powder, and the optimal energy density varied due to differences in the melting points between the CrFeCoNi (1414 °C), Cu (1084 °C), and Ti (1688 °C) powders. In addition, using elemental substances with lower melting points can affect the microstructure. At relatively high energy density, vaporization of an element reduces its amount, and this can lead to significant microstructural modifications.

2.9. Overall Comparison between AM Processes

A comparison of various AM processes used to produce HEAs in terms of production characteristics and microstructural phenomenon—PBF, DED, BJ and ME—is shown in Table 12. This mainly relates to feedstock material characteristics, printing design and parameters, and the related microstructures that are obtained. Altogether, it is clear that while PBF and DED processes tend to produce microstructures with preferred orientations, and consequently preferred properties, BJ and ME mostly produce a relatively large equiaxed grain structure. In addition, BJ and ME processes always required a post sintering phase, while PNF and DED do not need special post-processing treatment (apart from stress relief in the use of PBF when the printing is carried out on a cool tray).

3. Mechanical Properties

It is apparent that AM process parameters have a significant effect on the microstructure, and consequently, on the mechanical properties of HEAs. This insight relates to the well-known AM technologies used to produce HEA components. The most studied HEA composition is CrMnFeCoNi, which has been the focus of many publications. This was mainly attributed to the fact that this HEA does not form new phases during element segregation. The mechanical properties of CrMnFeCoNi HEAs produced by various AM processes in as-built condition are displayed in Figure 18, which reveals that the highest yield strength (YS) and UTS were obtained by the L-PBF process. The relatively increased strength can be attributed to the very high cooling rate of the L-PBF process, which leads to high residual stress and relatively reduced elongation. A satisfactory balance between the strength and ductility is usually obtained by an annealing treatment that is able to reduce strength and increase elongation.
The CrMnFeCoNi HEA produced by DED using BPD with a laser as the energy source showed relatively high strength with increased elongation compared to the case of L-PBF. Here, the DED process undergoes a high number of thermal cycles, which acts as an annealing heat treatment that leads to stress relief. The HEAs produced by EB-PBF and WAAM processes showed relatively similar mechanical properties. Overall, it seems that the differences in mechanical properties using the same energy source are minor and can be modified by post-processing heat treatment. In addition, the mechanical properties obtained by L-DED were similar to the HEA produced by conventional AMF process.
An additional example of the mechanical properties of Al0.3CrFeCoNi HEA produced by L-PBF and L-DED processes in comparison to the AMF process is shown in Figure 19. The L-PBF process demonstrated an increase in strength compared to both L-DED and AMF processes.

4. Corrosion Performance of HEAs Produced by AM Processes

HEAs are known for their superior corrosion resistance in extreme environments. However, their corrosion performance depends on the microstructure and inherent defects produced during the AM process. According to Niu et al. [52], the corrosion resistance of AlCrFeCoNi HEAs improves due to an increase in energy density. Finer microstructures with a large amount of B2 phase are obtained at high energy densities, which enhances the corrosion resistance. Higher energy density also reduces the number of defects (such as pores and lack of fusion) that can serve as initiation sites for pitting corrosion [161]. According to Kuwabara et al. [114], the use of EB-PBF for producing AlCrFeCoNi HEAs can cause element segregation due to preheating, leading to the formation of pitting sites in the Cr-depleted areas, whereas in the cast samples, pitting forms only at the grain boundaries. Another artifact of EB-PBF is microstructural changes in different sections of the printed material. Yamanaka et al. [110] found that the corrosion resistance in the bottom parts of AlCrFeCoNi HEAs (rich with FCC phases) is better than that in the top parts (with no FCC phases). Furthermore, the corrosion resistance of CrMnFeCoNi HEA produced by the LPBF process with single phase microstructure was improved compared to the cast samples due to relative grain refinement [61]. In parallel, VNbMoTaW HEAs showed similar corrosion resistance in LPBF and the cast samples, with a reduction in the pit dimensions compared to the cast samples [123].

5. Concluding

HEAs have earned significant attention in recent years due to their unique properties in terms of mechanical properties, thermal stability, and corrosion performance in hostile environments. However, the conventional methods for producing HEAs, such as AMF, mechanical alloying, plasma sintering, and physical vapor deposition, are extremely limited due to the complexity of the production process and consequent high cost. Hence, the potential of producing HEA components by AM, which are able to fabricate complex, near-net-shape components at an affordable cost, is quite attractive. Currently, the status of the most important AM technologies that are used to produce HEA parts, such as PBF, DED, ME and BJ, is well into the development phase.
Overall, the major limitation of all the main AM processes concerns the critical effect of the printing parameters on the properties of the final product. This limitation relates to two important aspects: (i) adequate synthesis between the elements composing the HEA to produce a homogeneous crystal structure with suitable microstructure and phase composition; and (ii) adequate physical properties, mainly with regard to printing defects and density in as-printed conditions and following post-processing heat treatment.
Relating to the feedstock material in the form of powder or wires that are used by the PBF and DED processes, it is preferable to work with a mixed elemental substance rather than a pre-alloyed material, especially if low cost is sought. In the case of mixed elemental powder, proper selection of the different powders in terms of grain size and morphology is essential. In the case of CCWs for DED processes, the wire assembly and cross section size should comply with the characteristics and capabilities of the energy source. This requires proper selection of different wire diameters and careful consideration of their plastic forming capabilities. In all cases, the criterion for success should focus on adequate synthesis and physical properties in terms of microstructural defects.

Author Contributions

Investigation, T.R.; writing—original draft preparation, T.R., A.S. and E.A.; supervision, A.S. and E.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Miracle, D.B.; Senkov, O.N. A critical review of high entropy alloys and related concepts. Acta Mater. 2017, 122, 448–511. [Google Scholar] [CrossRef] [Green Version]
  2. Gao, M.C.; Yeh, J.; Liaw, P.K.; Zhang, Y. High-Entropy Alloys; Springer: Berlin/Heidelberg, Germany, 2016. [Google Scholar]
  3. Sarswat, P.K.; Sarkar, S.; Murali, A.; Huang, W.; Tan, W.; Free, M.L. Additive manufactured new hybrid high entropy alloys derived from the AlCoFeNiSmTiVZr system. Appl. Surf. Sci. 2019, 476, 242–258. [Google Scholar] [CrossRef]
  4. Zhang, Y.; Zuo, T.T.; Tang, Z.; Gao, M.C.; Dahmen, K.A.; Liaw, P.K.; Lu, Z.P. Microstructures and properties of high-entropy alloys. Prog. Mater. Sci. 2014, 61, 1–93. [Google Scholar] [CrossRef]
  5. Hou, L.; Hui, J.; Yao, Y.; Chen, J.; Liu, J. Effects of Boron Content on microstructure and mechanical properties of AlFeCoNiBx High Entropy Alloy Prepared by vacuum arc melting. Vacuum 2019, 164, 212–218. [Google Scholar] [CrossRef]
  6. Cieslak, J.; Tobola, J.; Berent, K.; Marciszko, M. Phase composition of AlxFeNiCrCo high entropy alloys prepared by sintering and arc-melting methods. J. Alloy. Compd. 2018, 740, 264–272. [Google Scholar] [CrossRef]
  7. Torralba, J.M.; Alvaredo, P.; García-Junceda, A. High-entropy alloys fabricated via powder metallurgy. A critical review. Powder Metall. 2019, 62, 84–114. [Google Scholar] [CrossRef]
  8. Vaidya, M.; Muralikrishna, G.M.; Murty, B.S. High-entropy alloys by mechanical alloying: A review. J. Mater. Res. 2019, 34, 664–686. [Google Scholar] [CrossRef]
  9. Sriharitha, R.; Murty, B.; Kottada, R.S. Alloying, thermal stability and strengthening in spark plasma sintered AlxCoCrCuFeNi high entropy alloys. J. Alloy. Compd. 2014, 583, 419–426. [Google Scholar] [CrossRef]
  10. Xia, A.; Togni, A.; Hirn, S.; Bolelli, G.; Lusvarghi, L.; Franz, R. Angular-dependent deposition of MoNbTaVW HEA thin films by three different physical vapor deposition methods. Surf. Coatings Technol. 2020, 385, 125356. [Google Scholar] [CrossRef]
  11. Chen, S.; Tong, Y.; Liaw, P.K. Additive Manufacturing of High-Entropy Alloys: A Review. Entropy 2018, 20, 937. [Google Scholar] [CrossRef] [Green Version]
  12. Moghaddam, A.O.; Shaburova, N.A.; Samodurova, M.N.; Abdollahzadeh, A.; Trofimov, E.A. Additive manufacturing of high entropy alloys: A practical review. J. Mater. Sci. Technol. 2020, 77, 131–162. [Google Scholar] [CrossRef]
  13. Torralba, J.M.; Campos, M. High Entropy Alloys Manufactured by Additive Manufacturing. Metals 2020, 10, 639. [Google Scholar] [CrossRef]
  14. Kim, J.; Wakai, A.; Moridi, A. Materials and manufacturing renaissance: Additive manufacturing of high-entropy alloys. J. Mater. Res. 2020, 35, 1963–1983. [Google Scholar] [CrossRef]
  15. Zhang, C.; Zhu, J.; Zheng, H.; Li, H.; Liu, S.; Cheng, G.J. A review on microstructures and properties of high entropy alloys manufactured by selective laser melting. Int. J. Extreme Manuf. 2020, 2, 032003. [Google Scholar] [CrossRef]
  16. Arif, Z.U.; Khalid, M.Y.; Rehman, E.u. Laser-aided additive manufacturing of high entropy alloys: Processes, properties, and emerging applications. J. Manuf. Process. 2022, 78, 131–171. [Google Scholar] [CrossRef]
  17. Guo, Y.; Su, H.; Yang, P.; Zhao, Y.; Shen, Z.; Liu, Y.; Zhao, D.; Jiang, H.; Zhang, J.; Liu, L. A Review of Emerging Metallic System for High-Energy Beam Additive Manufacturing: Al–Co–Cr–Fe–Ni High Entropy Alloys. Acta Metall. Sin. 2022, 35, 1407–1423. [Google Scholar] [CrossRef]
  18. Han, C.; Fang, Q.; Shi, Y.; Tor, S.B.; Chua, C.K.; Zhou, K. Recent Advances on High-Entropy Alloys for 3D Printing. Adv. Mater. 2020, 32, e1903855. [Google Scholar] [CrossRef]
  19. Das, P.; Nandan, R.; Pandey, P.M. A Review on Corrosion Properties of High Entropy Alloys Fabricated by Additive Manufacturing. Trans. Indian Inst. Met. 2022, 75, 2465–2476. [Google Scholar] [CrossRef]
  20. Tokarewicz, M.; Grądzka-Dahlke, M. Review of Recent Research on AlCoCrFeNi High-Entropy Alloy. Metals 2021, 11, 1302. [Google Scholar] [CrossRef]
  21. Liu, H.; Yang, D.; Jiang, Q.; Jiang, Y.; Yang, W.; Liu, L.; Zhang, L. Additive manufacturing of metallic glasses and high-entropy alloys: Significance, unsettled issues, and future directions. J. Mater. Sci. Technol. 2022, 140, 79–120. [Google Scholar] [CrossRef]
  22. Kunce, I.; Polanski, M.; Bystrzycki, J. Structure and hydrogen storage properties of a high entropy ZrTiVCrFeNi alloy synthesized using Laser Engineered Net Shaping (LENS). Int. J. Hydrogen Energy 2013, 38, 12180–12189. [Google Scholar] [CrossRef]
  23. Leon, A.; Shirizly, A.; Aghion, E. Corrosion behavior of AlSi10Mg alloy produced by additive manufacturing (AM) vs. its counterpart gravity cast alloy. Metals 2016, 6, 148. [Google Scholar] [CrossRef] [Green Version]
  24. Leon, A.; Aghion, E. Effect of surface roughness on corrosion fatigue performance of AlSi10Mg alloy produced by Selective Laser Melting (SLM). Mater. Charact. 2017, 131, 188–194. [Google Scholar] [CrossRef]
  25. Zakay, A.; Aghion, E. Effect of Post-heat Treatment on the Corrosion Behavior of AlSi10Mg Alloy Produced by Additive Manufacturing. Jom 2019, 71, 1150–1157. [Google Scholar] [CrossRef]
  26. Leon, A.; Levy, G.K.; Ron, T.; Shirizly, A.; Aghion, E. The effect of strain rate on stress corrosion performance of Ti6Al4V alloy produced by additive manufacturing process. J. Mater. Res. Technol. 2020, 9, 4097–4105. [Google Scholar] [CrossRef]
  27. Leon, A.; Levy, G.K.; Ron, T.; Shirizly, A.; Aghion, E. The effect of hot isostatic pressure on the corrosion performance of Ti-6Al-4 V produced by an electron-beam melting additive manufacturing process. Addit. Manuf. 2020, 33, 101039. [Google Scholar] [CrossRef]
  28. Dong, B.; Wang, Z.; Pan, Z.; Muránsky, O.; Shen, C.; Reid, M.; Wu, B.; Chen, X.; Li, H. On the development of pseudo-eutectic AlCoCrFeNi2.1 high entropy alloy using Powder-bed Arc Additive Manufacturing (PAAM) process. Mater. Sci. Eng. A 2020, 802, 140639. [Google Scholar] [CrossRef]
  29. Jones, J.; Whittaker, M.; Buckingham, R.; Johnston, R.; Bache, M.; Clark, D. Microstructural characterisation of a nickel alloy processed via blown powder direct laser deposition (DLD). Mater. Des. 2017, 117, 47–57. [Google Scholar] [CrossRef] [Green Version]
  30. Isanaka, S.P.; Karnati, S.; Liou, F. Blown powder deposition of 4047 aluminum on 2024 aluminum substrates. Manuf. Lett. 2016, 7, 11–14. [Google Scholar] [CrossRef]
  31. Ron, T.; Levy, G.K.; Dolev, O.; Leon, A.; Shirizly, A.; Aghion, E. The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition. Metals 2020, 10, 98. [Google Scholar] [CrossRef] [Green Version]
  32. Ron, T.; Levy, G.K.; Dolev, O.; Leon, A.; Shirizly, A.; Aghion, E. Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process. Metals 2019, 9, 888. [Google Scholar] [CrossRef] [Green Version]
  33. Ron, T.; Dolev, O.; Leon, A.; Shirizly, A.; Aghion, E. Effect of Phase Transformation on Stress Corrosion Behavior of Additively Manufactured Austenitic Stainless Steel Produced by Directed Energy Deposition. Materials 2020, 14, 55. [Google Scholar] [CrossRef]
  34. Dolev, O.; Ron, T.; Aghion, E.; Shirizly, A. Effect of HIP Defects on the Mechanical Properties of Additive Manufactured Ti6Al4V Alloy. Metals 2022, 12, 1210. [Google Scholar] [CrossRef]
  35. Bassis, M.; Kotliar, A.; Koltiar, R.; Ron, T.; Leon, A.; Shirizly, A.; Aghion, E. The Effect of a Slow Strain Rate on the Stress Corrosion Resistance of Austenitic Stainless Steel Produced by the Wire Laser Additive Manufacturing Process. Metals 2021, 11, 1930. [Google Scholar] [CrossRef]
  36. Bassis, M.; Ron, T.; Leon, A.; Kotliar, A.; Kotliar, R.; Shirizly, A.; Aghion, E. The Influence of Intralayer Porosity and Phase Transition on Corrosion Fatigue of Additively Manufactured 316L Stainless Steel Obtained by Direct Energy Deposition Process. Materials 2022, 15, 5481. [Google Scholar] [CrossRef]
  37. Miyanaji, H.; Momenzadeh, N.; Yang, L. Effect of printing speed on quality of printed parts in Binder Jetting Process. Addit. Manuf. 2018, 20, 1–10. [Google Scholar] [CrossRef]
  38. Lores, A.; Azurmendi, N.; Agote, I.; Zuza, E. A review on recent developments in binder jetting metal additive manufacturing: Materials and process characteristics. Powder Met. 2019, 62, 267–296. [Google Scholar] [CrossRef]
  39. Terry, S.; Fidan, I.; Tantawi, K. Preliminary investigation into metal-material extrusion. Prog. Addit. Manuf. 2020, 6, 133–141. [Google Scholar] [CrossRef]
  40. Suwanpreecha, C.; Manonukul, A. A Review on Material Extrusion Additive Manufacturing of Metal and How It Compares with Metal Injection Moulding. Metals 2022, 12, 429. [Google Scholar] [CrossRef]
  41. Xia, M.; Chen, Y.; Chen, K.; Tong, Y.; Liang, X.; Shen, B. Synthesis of WTaMoNbZr refractory high-entropy alloy powder by plasma spheroidization process for additive manufacturing. J. Alloy. Compd. 2022, 917, 165501. [Google Scholar] [CrossRef]
  42. Singh, R.; Gupta, A.; Tripathi, O.; Srivastava, S.; Singh, B.; Awasthi, A.; Rajput, S.; Sonia, P.; Singhal, P.; Saxena, K.K. Powder bed fusion process in additive manufacturing: An overview. Mater. Today Proc. 2020, 26, 3058–3070. [Google Scholar] [CrossRef]
  43. King, W.E.; Anderson, A.T.; Ferencz, R.M.; Hodge, N.E.; Kamath, C.; Khairallah, S.A.; Rubenchik, A.M. Laser powder bed fusion additive manufacturing of metals; physics, computational, and materials challenges. Appl. Phys. Rev. 2015, 2, 041304. [Google Scholar] [CrossRef]
  44. Singh, D.D.; Mahender, T.; Reddy, A.R. Powder bed fusion process: A brief review. Mater. Today: Proc. 2020, 46, 350–355. [Google Scholar] [CrossRef]
  45. Kim, Y.-K.; Baek, M.-S.; Yang, S.; Lee, K.-A. In-situ formed oxide enables extraordinary high-cycle fatigue resistance in additively manufactured CoCrFeMnNi high-entropy alloy. Addit. Manuf. 2021, 38, 101832. [Google Scholar] [CrossRef]
  46. Kim, Y.-K.; Yang, S.; Lee, K.-A. Compressive creep behavior of selective laser melted CoCrFeMnNi high-entropy alloy strengthened by in-situ formation of nano-oxides. Addit. Manuf. 2020, 36, 101543. [Google Scholar] [CrossRef]
  47. Lin, D.; Xu, L.; Jing, H.; Han, Y.; Zhao, L.; Minami, F. Effects of annealing on the structure and mechanical properties of FeCoCrNi high-entropy alloy fabricated via selective laser melting. Addit. Manuf. 2020, 32, 101058. [Google Scholar] [CrossRef]
  48. Han, T.; Liu, Y.; Yang, D.; Qu, N.; Liao, M.; Lai, Z.; Jiang, M.; Zhu, J. Effect of annealing on microstructure and mechanical properties of AlCrFe2Ni2 medium entropy alloy fabricated by laser powder bed fusion additive manufacturing. Mater. Sci. Eng. A 2022, 839, 142868. [Google Scholar] [CrossRef]
  49. Tong, Z.; Liu, H.; Jiao, J.; Zhou, W.; Yang, Y.; Ren, X. Laser additive manufacturing of CrMnFeCoNi high entropy alloy: Microstructural evolution, high-temperature oxidation behavior and mechanism. Optics Laser Technol. 2020, 130, 106326. [Google Scholar] [CrossRef]
  50. Karimi, J.; Ma, P.; Jia, Y.; Prashanth, K. Linear patterning of high entropy alloy by additive manufacturing. Manuf. Lett. 2020, 24, 9–13. [Google Scholar] [CrossRef]
  51. Karlsson, D.; Marshal, A.; Johansson, F.; Schuisky, M.; Sahlberg, M.; Schneider, J.M.; Jansson, U. Elemental segregation in an AlCoCrFeNi high-entropy alloy—A comparison between selective laser melting and induction melting. J. Alloy. Compd. 2018, 784, 195–203. [Google Scholar] [CrossRef]
  52. Niu, P.; Li, R.; Yuan, T.; Zhu, S.; Chen, C.; Wang, M.; Huang, L. Microstructures and properties of an equimolar AlCoCrFeNi high entropy alloy printed by selective laser melting. Intermetallics 2018, 104, 24–32. [Google Scholar] [CrossRef]
  53. Peyrouzet, F.; Hachet, D.; Soulas, R.; Navone, C.; Godet, S.; Gorsse, S. Selective Laser Melting of Al0.3CoCrFeNi High-Entropy Alloy: Printability, Microstructure, and Mechanical Properties. Jom 2019, 71, 3443–3451. [Google Scholar] [CrossRef] [Green Version]
  54. Zhou, P.; Xiao, D.; Wu, Z.; Ou, X. Al0.5FeCoCrNi high entropy alloy prepared by selective laser melting with gas-atomized pre-alloy powders. Mater. Sci. Eng. A 2018, 739, 86–89. [Google Scholar] [CrossRef]
  55. Wang, S.; Li, Y.; Zhang, D.; Yang, Y.; Manladan, S.M.; Luo, Z. Microstructure and mechanical properties of high strength AlCoCrFeNi2.1 eutectic high entropy alloy prepared by selective laser melting (SLM). Mater. Lett. 2022, 310, 131511. [Google Scholar] [CrossRef]
  56. Guo, Y.; Su, H.; Zhou, H.; Shen, Z.; Liu, Y.; Zhang, J.; Liu, L.; Fu, H. Unique strength-ductility balance of AlCoCrFeNi2.1 eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting. J. Mater. Sci. Technol. 2021, 111, 298–306. [Google Scholar] [CrossRef]
  57. Lu, Y.; Wu, X.; Fu, Z.; Yang, Q.; Zhang, Y.; Liu, Q.; Li, T.; Tian, Y.; Tan, H.; Li, Z.; et al. Ductile and ultrahigh-strength eutectic high-entropy alloys by large-volume 3D printing. J. Mater. Sci. Technol. 2022, 126, 15–21. [Google Scholar] [CrossRef]
  58. Ren, J.; Zhang, Y.; Zhao, D.; Chen, Y.; Guan, S.; Liu, Y.; Liu, L.; Peng, S.; Kong, F.; Poplawsky, J.D.; et al. Strong yet ductile nanolamellar high-entropy alloys by additive manufacturing. Nature 2022, 608, 62–68. [Google Scholar] [CrossRef]
  59. Chen, X.; Kong, J.; Li, J.; Feng, S.; Li, H.; Wang, Q.; Liang, Y.; Dong, K.; Yang, Y. High-strength AlCoCrFeNi2.1 eutectic high entropy alloy with ultrafine lamella structure via additive manufacturing. Mater. Sci. Eng. A 2022, 854, 143816. [Google Scholar] [CrossRef]
  60. Vogiatzief, D.; Evirgen, A.; Gein, S.; Molina, V.R.; Weisheit, A.; Pedersen, M. Laser Powder Bed Fusion and Heat Treatment of an AlCrFe2Ni2 High Entropy Alloy. Front. Mater. 2020, 7, 248. [Google Scholar] [CrossRef]
  61. Luo, S.; Gao, P.; Yu, H.; Yang, J.; Wang, Z.; Zeng, X. Selective laser melting of an equiatomic AlCrCuFeNi high-entropy alloy: Processability, non-equilibrium microstructure and mechanical behavior. J. Alloy Compd. 2019, 771, 387–397. [Google Scholar] [CrossRef]
  62. Luo, S.; Zhao, C.; Su, Y.; Liu, Q.; Wang, Z. Selective laser melting of dual phase AlCrCuFeNix high entropy alloys: Formability, heterogeneous microstructures and deformation mechanisms. Addit. Manuf. 2020, 31, 100925. [Google Scholar] [CrossRef]
  63. Yuan, B.; Li, C.; Dong, Y.; Yang, Y.; Zhang, P.; Zhang, Z. Selective laser melting of the Al0.3CoCrFeNiCu high-entropy alloy: Processing parameters, microstructure and mechanical properties. Mater. Des. 2022, 220, 110847. [Google Scholar] [CrossRef]
  64. Zhang, M.; Zhou, X.; Wang, D.; Zhu, W.; Li, J.; Zhao, Y.F. AlCoCuFeNi high-entropy alloy with tailored microstructure and outstanding compressive properties fabricated via selective laser melting with heat treatment. Mater. Sci. Eng. A 2018, 743, 773–784. [Google Scholar] [CrossRef]
  65. Kuzminova, Y.; Firsov, D.; Dudin, A.; Sergeev, S.; Zhilyaev, A.; Dyakov, A.; Chupeeva, A.; Alekseev, A.; Martynov, D.; Akhatov, I.; et al. The effect of the parameters of the powder bed fusion process on the microstructure and mechanical properties of CrFeCoNi medium-entropy alloys. Intermetallics 2020, 116, 106651. [Google Scholar] [CrossRef]
  66. Brif, Y.; Thomas, M.; Todd, I. The use of high-entropy alloys in additive manufacturing. Scr. Mater. 2015, 99, 93–96. [Google Scholar] [CrossRef]
  67. Lin, D.; Xu, L.; Jing, H.; Han, Y.; Zhao, L.; Zhang, Y.; Li, H. A strong, ductile, high-entropy FeCoCrNi alloy with fine grains fabricated via additive manufacturing and a single cold deformation and annealing cycle. Addit. Manuf. 2020, 36, 101591. [Google Scholar] [CrossRef]
  68. Zhao, W.; Han, J.-K.; Kuzminova, Y.O.; Evlashin, S.A.; Zhilyaev, A.P.; Pesin, A.M.; Jang, J.-I.; Liss, K.-D.; Kawasaki, M. Significance of grain refinement on micro-mechanical properties and structures of additively-manufactured CoCrFeNi high-entropy alloy. Mater. Sci. Eng. A 2021, 807, 140898. [Google Scholar] [CrossRef]
  69. Kuzminova, Y.O.; Kudryavtsev, E.A.; Han, J.-K.; Kawasaki, M.; Evlashin, S.A. Phase and structural changes during heat treatment of additive manufactured CrFeCoNi high-entropy alloy. J. Alloy. Compd. 2021, 889, 161495. [Google Scholar] [CrossRef]
  70. Lin, D.; Xi, X.; Li, X.; Hu, J.; Xu, L.; Han, Y.; Zhang, Y.; Zhao, L. High-temperature mechanical properties of FeCoCrNi high-entropy alloys fabricated via selective laser melting. Mater. Sci. Eng. A 2021, 832, 142354. [Google Scholar] [CrossRef]
  71. Peng, Y.; Jia, C.; Song, L.; Bian, Y.; Tang, H.; Cai, G.; Zhong, G. The manufacturing process optimization and the mechanical properties of FeCoCrNi high entropy alloys fabricated by selective laser melting. Intermetallics 2022, 145, 1279–1290. [Google Scholar] [CrossRef]
  72. Sun, Z.; Tan, X.; Wang, C.; Descoins, M.; Mangelinck, D.; Tor, S.B.; Jägle, E.A.; Zaefferer, S.; Raabe, D. Reducing hot tearing by grain boundary segregation engineering in additive manufacturing: Example of an AlxCoCrFeNi high-entropy alloy. Acta Mater. 2020, 204, 116505. [Google Scholar] [CrossRef]
  73. Kuzminova, Y.; Shibalova, A.; Evlashin, S.; Shishkovsky, I.; Krakhmalev, P. Structural effect of low Al content in the in-situ additive manufactured CrFeCoNiAlx high-entropy alloy. Mater. Lett. 2021, 303, 130487. [Google Scholar] [CrossRef]
  74. Zhu, Z.; Nguyen, Q.; Ng, F.; An, X.; Liao, X.; Liaw, P.; Nai, S.; Wei, J. Hierarchical microstructure and strengthening mechanisms of a CoCrFeNiMn high entropy alloy additively manufactured by selective laser melting. Scr. Mater. 2018, 154, 20–24. [Google Scholar] [CrossRef]
  75. Li, R.; Niu, P.; Yuan, T.; Cao, P.; Chen, C.; Zhou, K. Selective laser melting of an equiatomic CoCrFeMnNi high-entropy alloy: Processability, non-equilibrium microstructure and mechanical property. J. Alloys Compd. 2018, 746, 125–134. [Google Scholar] [CrossRef]
  76. Niu, P.; Li, R.; Zhu, S.; Wang, M.; Chen, C.; Yuan, T. Hot cracking, crystal orientation and compressive strength of an equimolar CoCrFeMnNi high-entropy alloy printed by selective laser melting. Opt. Laser Technol. 2020, 127, 106147. [Google Scholar] [CrossRef]
  77. Piglione, A.; Dovgyy, B.; Liu, C.; Gourlay, C.; Hooper, P.; Pham, M. Printability and microstructure of the CoCrFeMnNi high-entropy alloy fabricated by laser powder bed fusion. Mater. Lett. 2018, 224, 22–25. [Google Scholar] [CrossRef]
  78. Xu, Z.; Zhang, H.; Li, W.; Mao, A.; Wang, L.; Song, G.; He, Y. Microstructure and nanoindentation creep behavior of CoCrFeMnNi high-entropy alloy fabricated by selective laser melting. Addit. Manuf. 2019, 28, 766–771. [Google Scholar] [CrossRef]
  79. Xu, Z.; Zhang, H.; Du, X.; He, Y.; Luo, H.; Song, G.; Mao, L.; Zhou, T.; Wang, L. Corrosion resistance enhancement of CoCrFeMnNi high-entropy alloy fabricated by additive manufacturing. Corros. Sci. 2020, 177, 108954. [Google Scholar] [CrossRef]
  80. Litwa, P.; Hernandez-Nava, E.; Guan, D.; Goodall, R.; Wika, K.K. The additive manufacture processing and machinability of CrMnFeCoNi high entropy alloy. Mater. Des. 2020, 198, 109380. [Google Scholar] [CrossRef]
  81. Wang, H.; Zhu, Z.; Chen, H.; Wang, A.; Liu, J.; Liu, H.; Zheng, R.; Nai, S.; Primig, S.; Babu, S.; et al. Effect of cyclic rapid thermal loadings on the microstructural evolution of a CrMnFeCoNi high-entropy alloy manufactured by selective laser melting. Acta Mater. 2020, 196, 609–625. [Google Scholar] [CrossRef]
  82. Jin, M.; Piglione, A.; Dovgyy, B.; Hosseini, E.; Hooper, P.A.; Holdsworth, S.R.; Pham, M.-S. Cyclic plasticity and fatigue damage of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion. Addit. Manuf. 2020, 36, 101584. [Google Scholar] [CrossRef]
  83. Jin, M.; Hosseini, E.; Holdsworth, S.; Pham, M.-S. Thermally activated dependence of fatigue behaviour of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion. Addit. Manuf. 2022, 51, 102600. [Google Scholar] [CrossRef]
  84. Kim, Y.-K.; Suh, J.-Y.; Lee, K.-A. Effect of gaseous hydrogen embrittlement on the mechanical properties of additively manufactured CrMnFeCoNi high-entropy alloy strengthened by in-situ formed oxide. Mater. Sci. Eng. A 2020, 796, 140039. [Google Scholar] [CrossRef]
  85. Kim, Y.-K.; Kim, M.-C.; Lee, K.-A. 1.45 GPa ultrastrong cryogenic strength with superior impact toughness in the in-situ nano oxide reinforced CrMnFeCoNi high-entropy alloy matrix nanocomposite manufactured by laser powder bed fusion. J. Mater. Sci. Technol. 2021, 97, 10–19. [Google Scholar] [CrossRef]
  86. He, X.Y.; Wang, H.; Zhu, Z.G.; Wang, L.Z.; Liu, J.Q.; Haghdadi, N.; Nai, S.M.L.; Huang, J.; Primig, S.; Ringer, S.P.; et al. Texture evolution in a CrMnFeCoNi high-entropy alloy manufactured by laser powder bed fusion. J. Mater. Sci. 2022, 57, 9714–9725. [Google Scholar] [CrossRef]
  87. Karthik, G.; Kim, Y.; Kim, E.S.; Zargaran, A.; Sathiyamoorthi, P.; Park, J.M.; Jeong, S.G.; Gu, G.H.; Amanov, A.; Ungar, T.; et al. Gradient heterostructured laser-powder bed fusion processed CoCrFeMnNi high entropy alloy. Addit. Manuf. 2022, 59, 103131. [Google Scholar] [CrossRef]
  88. Liu, C.; Zhu, K.; Ding, W.; Liu, Y.; Chen, G.; Qu, X. Additive manufacturing of WMoTaTi refractory high-entropy alloy by employing fluidised powders. Powder Met. 2022, 65, 413–425. [Google Scholar] [CrossRef]
  89. Ishimoto, T.; Ozasa, R.; Nakano, K.; Weinmann, M.; Schnitter, C.; Stenzel, M.; Matsugaki, A.; Nagase, T.; Matsuzaka, T.; Todai, M.; et al. Development of TiNbTaZrMo bio-high entropy alloy (BioHEA) super-solid solution by selective laser melting, and its improved mechanical property and biocompatibility. Scr. Mater 2021, 194, 113658. [Google Scholar] [CrossRef]
  90. Yang, F.; Wang, L.; Wang, Z.; Wu, Q.; Zhou, K.; Lin, X.; Huang, W. Ultra strong and ductile eutectic high entropy alloy fabricated by selective laser melting. J. Mater. Sci. Technol. 2021, 106, 128–132. [Google Scholar] [CrossRef]
  91. Wang, Y.; Li, R.; Niu, P.; Zhang, Z.; Yuan, T.; Yuan, J.; Li, K. Microstructures and properties of equimolar AlCoCrCuFeNi high-entropy alloy additively manufactured by selective laser melting. Intermetallics 2020, 120, 106746. [Google Scholar] [CrossRef]
  92. Lin, W.-C.; Chang, Y.-J.; Hsu, T.-H.; Gorsse, S.; Sun, F.; Furuhara, T.; Yeh, A.-C. Microstructure and tensile property of a precipitation strengthened high entropy alloy processed by selective laser melting and post heat treatment. Addit. Manuf. 2020, 36, 101601. [Google Scholar] [CrossRef]
  93. Mu, Y.; He, L.; Deng, S.; Jia, Y.; Jia, Y.; Wang, G.; Zhai, Q.; Liaw, P.K.; Liu, C.-T. A high-entropy alloy with dislocation-precipitate skeleton for ultrastrength and ductility. Acta Mater. 2022, 232, 117975. [Google Scholar] [CrossRef]
  94. Wu, Y.; Zhao, X.; Chen, Q.; Yang, C.; Jiang, M.; Liu, C.; Jia, Z.; Chen, Z.; Yang, T.; Liu, Z. Strengthening and fracture mechanisms of a precipitation hardening high-entropy alloy fabricated by selective laser melting. Virtual Phys. Prototyp. 2022, 17, 451–467. [Google Scholar] [CrossRef]
  95. Yao, H.; Tan, Z.; He, D.; Zhou, Z.; Zhou, Z.; Xue, Y.; Cui, L.; Chen, L.; Wang, G.; Yang, Y. High strength and ductility AlCrFeNiV high entropy alloy with hierarchically heterogeneous microstructure prepared by selective laser melting. J. Alloy. Compd. 2019, 813, 152196. [Google Scholar] [CrossRef]
  96. Agrawal, P.; Haridas, R.S.; Thapliyal, S.; Yadav, S.; Mishra, R.S.; McWilliams, B.A.; Cho, K.C. Metastable high entropy alloys: An excellent defect tolerant material for additive manufacturing. Mater. Sci. Eng. A 2021, 826, 142005. [Google Scholar] [CrossRef]
  97. Thapliyal, S.; Nene, S.S.; Agrawal, P.; Wang, T.; Morphew, C.; Mishra, R.S.; McWilliams, B.A.; Cho, K.C. Damage-tolerant, corrosion-resistant high entropy alloy with high strength and ductility by laser powder bed fusion additive manufacturing. Addit. Manuf. 2020, 36, 101455. [Google Scholar] [CrossRef]
  98. Agrawal, P.; Thapliyal, S.; Nene, S.; Mishra, R.; McWilliams, B.; Cho, K. Excellent strength-ductility synergy in metastable high entropy alloy by laser powder bed additive manufacturing. Addit. Manuf. 2020, 32, 101098. [Google Scholar] [CrossRef]
  99. Fujieda, T.; Chen, M.; Shiratori, H.; Kuwabara, K.; Yamanaka, K.; Koizumi, Y.; Chiba, A.; Watanabe, S. Mechanical and corrosion properties of CoCrFeNiTi-based high-entropy alloy additive manufactured using selective laser melting. Addit. Manuf. 2019, 25, 412–420. [Google Scholar] [CrossRef]
  100. Zhao, Y.; Lau, K.B.; Teh, W.H.; Lee, J.J.; Wei, F.; Lin, M.; Wang, P.; Tan, C.C.; Ramamurty, U. Compositionally graded CoCrFeNiTix high-entropy alloys manufactured by laser powder bed fusion: A combinatorial assessment. J. Alloys Compd. 2021, 883, 160825. [Google Scholar] [CrossRef]
  101. Farquhar, L.; Maddison, G.; Hardwick, L.; Livera, F.; Todd, I.; Goodall, R. In-Situ Alloying of CoCrFeNiX High Entropy Alloys by Selective Laser Melting. Metals 2022, 12, 456. [Google Scholar] [CrossRef]
  102. Su, Y.; Luo, S.; Wang, Z. Microstructure evolution and cracking behaviors of additively manufactured AlxCrCuFeNi2 high entropy alloys via selective laser melting. J. Alloy. Compd. 2020, 842, 155823. [Google Scholar] [CrossRef]
  103. Gu, Z.; Su, X.; Peng, W.; Guo, W.; Xi, S.; Zhang, X.; Tu, H.; Gao, Y.; Wu, H. An important improvement of strength and ductility on a new type of CoCr2.5FeNi2TiW0.5 high entropy alloys under two different protective gases by selective laser melting. J. Alloy. Compd. 2021, 868, 159088. [Google Scholar] [CrossRef]
  104. Yang, X.; Zhou, Y.; Xi, S.; Chen, Z.; Wei, P.; He, C.; Li, T.; Gao, Y.; Wu, H. Additively manufactured fine grained Ni6Cr4WFe9Ti high entropy alloys with high strength and ductility. Mater. Sci. Eng. A 2019, 767, 138394. [Google Scholar] [CrossRef]
  105. Zhu, X.; Wang, G.; Wang, X.; Zhao, G. Microstructure and mechanical properties of Al0.3FeCoCrNi high entropy alloy processed by laser powder bed fusion using FeCoCrNi and Al powder mixture. Mater. Sci. Eng. A 2022, 848, 143468. [Google Scholar] [CrossRef]
  106. Geng, Z.; Chen, C.; Li, R.; Luo, J.; Zhou, K. Composition inhomogeneity reduces cracking susceptibility in additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy produced by laser powder bed fusion. Addit. Manuf. 2022, 56, 102941. [Google Scholar] [CrossRef]
  107. Vogiatzief, D.; Evirgen, A.; Pedersen, M.; Hecht, U. Laser powder bed fusion of an Al-Cr-Fe-Ni high-entropy alloy produced by blending of prealloyed and elemental powder: Process parameters, microstructures and mechanical properties. J. Alloy. Compd. 2022, 918, 165658. [Google Scholar] [CrossRef]
  108. Chen, P.; Li, S.; Zhou, Y.; Yan, M.; Attallah, M.M. Fabricating CoCrFeMnNi high entropy alloy via selective laser melting in-situ alloying. J. Mater. Sci. Technol. 2020, 43, 40–43. [Google Scholar] [CrossRef]
  109. Wang, H.; Chen, J.; Luo, H.; Wang, D.; Song, C.; Yao, X.; Chen, P.; Yan, M. Bimetal printing of high entropy alloy/metallic glass by laser powder bed fusion additive manufacturing. Intermetallics 2022, 141, 107430. [Google Scholar] [CrossRef]
  110. Yamanaka, K.; Shiratori, H.; Mori, M.; Omura, K.; Fujieda, T.; Kuwabara, K.; Chiba, A. Corrosion mechanism of an equimolar AlCoCrFeNi high-entropy alloy additively manufactured by electron beam melting. npj Mater. Degrad. 2020, 4, 24. [Google Scholar] [CrossRef]
  111. Fujieda, T.; Shiratori, H.; Kuwabara, K.; Kato, T.; Yamanaka, K.; Koizumi, Y.; Chiba, A. First demonstration of promising selective electron beam melting method for utilizing high-entropy alloys as engineering materials. Mater. Lett. 2015, 159, 12–15. [Google Scholar] [CrossRef]
  112. Shiratori, H.; Fujieda, T.; Yamanaka, K.; Koizumi, Y.; Kuwabara, K.; Kato, T.; Chiba, A. Relationship between the microstructure and mechanical properties of an equiatomic AlCoCrFeNi high-entropy alloy fabricated by selective electron beam melting. Mater. Sci. Eng. A 2016, 656, 39–46. [Google Scholar] [CrossRef]
  113. Zhang, M.; Zhou, X.; Wang, D.; He, L.; Ye, X.; Zhang, W. Additive manufacturing of in-situ strengthened dual-phase AlCoCuFeNi high-entropy alloy by selective electron beam melting. J. Alloy. Compd. 2021, 893, 162259. [Google Scholar] [CrossRef]
  114. Kuwabara, K.; Shiratori, H.; Fujieda, T.; Yamanaka, K.; Koizumi, Y.; Chiba, A. Mechanical and corrosion properties of AlCoCrFeNi high-entropy alloy fabricated with selective electron beam melting. Addit. Manuf. 2018, 23, 264–271. [Google Scholar] [CrossRef]
  115. Wang, P.; Huang, P.; Ng, F.L.; Sin, W.J.; Lu, S.; Nai, M.L.S.; Dong, Z.; Wei, J. Additively manufactured CoCrFeNiMn high-entropy alloy via pre-alloyed powder. Mater. Des. 2019, 168, 107576. [Google Scholar] [CrossRef]
  116. Eißmann, N.; Klöden, B.; Weißgärber, T.; Kieback, B. High-entropy alloy CoCrFeMnNi produced by powder metallurgy. Powder Met. 2017, 60, 184–197. [Google Scholar] [CrossRef]
  117. Cagirici, M.; Wang, P.; Ng, F.L.; Nai, M.L.S.; Ding, J.; Wei, J. Additive manufacturing of high-entropy alloys by thermophysical calculations and in situ alloying. J. Mater. Sci. Technol. 2021, 94, 53–66. [Google Scholar] [CrossRef]
  118. Fujieda, T.; Shiratori, H.; Kuwabara, K.; Hirota, M.; Kato, T.; Yamanaka, K.; Koizumi, Y.; Chiba, A.; Watanabe, S. CoCrFeNiTi-based high-entropy alloy with superior tensile strength and corrosion resistance achieved by a combination of additive manufacturing using selective electron beam melting and solution treatment. Mater Lett. 2017, 189, 148–151. [Google Scholar] [CrossRef]
  119. Karimi, J.; Kollo, L.; Rahmani, R.; Ma, P.; Jia, Y.; Prashanth, K. Selective laser melting of in-situ CoCrFeMnNi high entropy alloy: Effect of remelting. J. Manuf. Process. 2022, 84, 55–63. [Google Scholar] [CrossRef]
  120. Hou, Y.; Su, H.; Zhang, H.; Wang, X.; Wang, C. Fabricating Homogeneous FeCoCrNi High-Entropy Alloys via SLM In Situ Alloying. Metals 2021, 11, 942. [Google Scholar] [CrossRef]
  121. Zhang, H.; Zhao, Y.; Huang, S.; Zhu, S.; Wang, F.; Li, D. Manufacturing and Analysis of High-Performance Refractory High-Entropy Alloy via Selective Laser Melting (SLM). Materials 2019, 12, 720. [Google Scholar] [CrossRef] [Green Version]
  122. Huber, F.; Bartels, D.; Schmidt, M. In-Situ Alloy Formation of a WMoTaNbV Refractory Metal High Entropy Alloy by Laser Powder Bed Fusion (PBF-LB/M). Materials 2021, 14, 3095. [Google Scholar] [CrossRef] [PubMed]
  123. Ron, T.; Leon, A.; Popov, V.; Strokin, E.; Eliezer, D.; Shirizly, A.; Aghion, E. Synthesis of Refractory High-Entropy Alloy WTaMoNbV by Powder Bed Fusion Process Using Mixed Elemental Alloying Powder. Materials 2022, 15, 4043. [Google Scholar] [CrossRef]
  124. Li, Q.; Chen, X.; Zhang, J.; Jayalakshmi, S.; Arvind Singh, R. Investigation of the Effect of the Thermo-Mechanical Processing of Additively Manufactured CoCrFeNiAl0.4 High-Entropy Alloy. Adv. Eng. Mater. 2022, 24, 2101628. [Google Scholar] [CrossRef]
  125. Popov, V.V., Jr.; Katz-Demyanetz, A.; Koptyug, A.; Bamberger, M. Selective electron beam melting of Al0.5CrMoNbTa0.5 high entropy alloys using elemental powder blend. Heliyon 2019, 5, e01188. [Google Scholar] [CrossRef] [Green Version]
  126. Katz-Demyanetz, A.; Gorbachev, I.; Eshed, E.; Popov, V.; Bamberger, M. High entropy Al0.5CrMoNbTa0.5 alloy: Additive manufacturing vs. casting vs. CALPHAD approval calculations. Mater. Charact. 2020, 167, 110505. [Google Scholar] [CrossRef]
  127. Lin, D.; Xu, L.; Li, X.; Jing, H.; Qin, G.; Pang, H.; Minami, F. A Si-containing FeCoCrNi high-entropy alloy with high strength and ductility synthesized in situ via selective laser melting. Addit. Manuf. 2020, 35, 101340. [Google Scholar] [CrossRef]
  128. Wang, J.; Lu, Y.; Jia, F.; Xia, W.; Lin, F.; Han, J.; Wang, R.; Pan, Z.; Li, H.; Jiang, Z. Effects of inter-layer remelting frequency on the microstructure evolution and mechanical properties of equimolar CoCrFeNiMn high entropy alloys during in-situ powder-bed arc additive manufacturing (PBAAM) process. J. Mater. Sci. Technol. 2022, 113, 90–104. [Google Scholar] [CrossRef]
  129. Zhang, H.; Zhao, Y.; Cai, J.; Ji, S.; Geng, J.; Sun, X.; Li, D. High-strength NbMoTaX refractory high-entropy alloy with low stacking fault energy eutectic phase via laser additive manufacturing. Mater. Des. 2021, 201, 109462. [Google Scholar] [CrossRef]
  130. Dong, B.; Wang, Z.; Zhu, H.; Muránsky, O.; Qiu, Z.; Shen, C.; Pan, Z.; Li, H. Low neutron cross-section FeCrVTiNi based high-entropy alloys: Design, additive manufacturing and characterization. Microstructures 2022, 2, 2022003. [Google Scholar] [CrossRef]
  131. Ahn, D. Directed energy deposition (DED) process: State of the art. Int. J. Precis. Eng. Manuf. Green Technol. 2021, 8, 703–742. [Google Scholar] [CrossRef]
  132. Singh, A.; Kapil, S.; Das, M. A comprehensive review of the methods and mechanisms for powder feedstock handling in directed energy deposition. Addit. Manuf. 2020, 35, 101388. [Google Scholar] [CrossRef]
  133. Prasad, H.S.; Brueckner, F.; Kaplan, A.F. Powder incorporation and spatter formation in high deposition rate blown powder directed energy deposition. Addit. Manuf. 2020, 35, 101413. [Google Scholar] [CrossRef]
  134. Tong, Z.; Liu, H.; Jiao, J.; Zhou, W.; Yang, Y.; Ren, X. Improving the strength and ductility of laser directed energy deposited CrMnFeCoNi high-entropy alloy by laser shock peening. Addit. Manuf. 2020, 35, 101417. [Google Scholar] [CrossRef]
  135. Sui, Q.; Wang, Z.; Wang, J.; Xu, S.; Zhao, F.; Gong, L.; Liu, B.; Liu, J.; Liu, G. The microstructure and mechanical properties of the additive manufactured AlCoCrFeNi high entropy alloy. Mater. Sci. Eng. A 2021, 833, 142507. [Google Scholar] [CrossRef]
  136. Zhou, K.; Li, J.; Wu, Q.; Zhang, Z.; Wang, Z.; Wang, J. Remelting induced fully-equiaxed microstructures with anomalous eutectics in the additive manufactured Ni32Co30Cr10Fe10Al18 eutectic high-entropy alloy. Scr. Mater. 2021, 201, 113952. [Google Scholar] [CrossRef]
  137. Kunce, I.; Polanski, M.; Karczewski, K.; Plocinski, T.; Kurzydlowski, K. Microstructural characterisation of high-entropy alloy AlCoCrFeNi fabricated by laser engineered net shaping. J. Alloy. Compd. 2015, 648, 751–758. [Google Scholar] [CrossRef]
  138. Yang, S.; Liu, Z.; Pi, J. Microstructure and wear behavior of the AlCrFeCoNi high-entropy alloy fabricated by additive manufacturing. Mater. Lett. 2019, 261, 127004. [Google Scholar] [CrossRef]
  139. Cai, Y.; Li, X.; Xia, H.; Cui, Y.; Manladan, S.M.; Zhu, L.; Shan, M.; Sun, D.; Wang, T.; Lv, X.; et al. Fabrication of laminated high entropy alloys using differences in laser melting deposition characteristics of FeCoCrNi and FeCoCrNiAl. J. Manuf. Process. 2021, 72, 294–308. [Google Scholar] [CrossRef]
  140. Ocelík, V.; Janssen, N.; Smith, S.N.; De Hosson, J.T.M. Additive Manufacturing of High-Entropy Alloys by Laser Processing. Jom 2016, 68, 1810–1818. [Google Scholar] [CrossRef] [Green Version]
  141. Wang, R.; Zhang, K.; Davies, C.; Wu, X. Evolution of microstructure, mechanical and corrosion properties of AlCoCrFeNi high-entropy alloy prepared by direct laser fabrication. J. Alloy. Compd. 2017, 694, 971–981. [Google Scholar] [CrossRef]
  142. Sistla, H.R.; Newkirk, J.W.; Frank Liou, F. Effect of Al/Ni ratio, heat treatment on phase transformations and microstructure of AlxFeCoCrNi2−x (x=0.3, 1) high entropy alloys. Mater Des. 2015, 81, 113–121. [Google Scholar] [CrossRef]
  143. Chen, X.; Yan, L.; Karnati, S.; Zhang, Y.; Liou, F. Fabrication and characterization of AlxCoFeNiCu1−x high entropy alloys by laser metal deposition. Coatings 2017, 7, 47. [Google Scholar] [CrossRef] [Green Version]
  144. Joseph, J.; Stanford, N.; Hodgson, P.; Fabijanic, D.M. Tension/compression asymmetry in additive manufactured face centered cubic high entropy alloy. Scr. Mater. 2017, 129, 30–34. [Google Scholar] [CrossRef]
  145. Peng, H.; Xie, S.; Niu, P.; Zhang, Z.; Yuan, T.; Ren, Z.; Wang, X.; Zhao, Y.; Li, R. Additive manufacturing of Al0.3CoCrFeNi high-entropy alloy by powder feeding laser melting deposition. J. Alloy. Compd. 2021, 862, 158286. [Google Scholar] [CrossRef]
  146. Nartu, M.S.K.K.Y.; Alam, T.; Dasari, S.; Mantri, S.A.; Gorsse, S.; Siller, H.; Dahotre, N.; Banerjee, R. Enhanced tensile yield strength in laser additively manufactured Al0.3CoCrFeNi high entropy alloy. Materialia 2020, 9, 100522. [Google Scholar] [CrossRef]
  147. Joseph, J.; Hodgson, P.; Jarvis, T.; Wu, X.; Stanford, N.; Fabijanic, D. Effect of hot isostatic pressing on the microstructure and mechanical properties of additive manufactured AlxCoCrFeNi high entropy alloys. Mater. Sci. Eng. A 2018, 733, 59–70. [Google Scholar] [CrossRef]
  148. Joseph, J.; Jarvis, T.; Wu, X.; Stanford, N.; Hodgson, P.; Fabijanic, D.M. Comparative study of the microstructures and mechanical properties of direct laser fabricated and arc-melted AlxCoCrFeNi high entropy alloys. Mater. Sci. Eng. A 2015, 633, 184–193. [Google Scholar] [CrossRef]
  149. Chao, Q.; Guo, T.; Jarvis, T.; Wu, X.; Hodgson, P.; Fabijanic, D. Direct laser deposition cladding of AlxCoCrFeNi high entropy alloys on a high-temperature stainless steel. Surf. Coat. Technol. 2017, 332, 440–451. [Google Scholar] [CrossRef]
  150. Li, Q.; Chen, X.; Chen, X.; Siddiquee, A.N.; Deev, V.B.; Konovalov, S.; Wen, M. Microstructure evolution of additively manufactured CoCrFeNiAl0.4 high-entropy alloy under thermo-mechanical processing. J. Mater. Res. Technol. 2022, 16, 442–450. [Google Scholar] [CrossRef]
  151. Zhang, Y.; Chen, X.; Jayalakshmi, S.; Singh, R.A.; Deev, V.B.; Prusov, E.S. Factors determining solid solution phase formation and stability in CoCrFeNiX0.4 (X=Al, Nb, Ta) high entropy alloys fabricated by powder plasma arc additive manufacturing. J. Alloy. Compd. 2021, 857, 157625. [Google Scholar] [CrossRef]
  152. Zhang, Y.; Shen, Q.; Chen, X.; Jayalakshmi, S.; Singh, R.A.; Konovalov, S.; Deev, V.B.; Prusov, E.S. Strengthening mechanisms in CoCrFeNiX0.4 (Al, Nb, Ta) high entropy alloys fabricated by powder plasma arc additive manufacturing. Nanomaterials 2021, 11, 721. [Google Scholar] [CrossRef] [PubMed]
  153. Joseph, J.; Imran, M.; Hodgson, P.D.; Barnett, M.R.; Fabijanic, D.M. Towards the large-scale production and strength prediction of near-eutectic AlxCoCrFeNi2.1 alloys by additive manufacturing. Manuf. Lett. 2020, 25, 16–20. [Google Scholar] [CrossRef]
  154. Shen, Q.; Xue, J.; Zheng, Z.; Yu, X.; Ou, N. Effect of heat treatment on microstructure and mechanical properties of Al1.2CoCrFeNi2.1 high-entropy alloy fabricated by powder plasma arc additive manufacturing. Mater. Sci. Eng. A 2022, 857, 144129. [Google Scholar] [CrossRef]
  155. Zhu, Y.; Zhou, S.; Xiong, Z.; Liang, Y.-J.; Xue, Y.; Wang, L. Enabling stronger eutectic high-entropy alloys with larger ductility by 3D printed directional lamellae. Addit. Manuf. 2021, 39, 101901. [Google Scholar] [CrossRef]
  156. Huang, L.; Sun, Y.; Chen, N.; Luan, H.; Le, G.; Liu, X.; Ji, Y.; Lu, Y.; Liaw, P.K.; Yang, X.; et al. Simultaneously enhanced strength-ductility of AlCoCrFeNi2.1 eutectic high-entropy alloy via additive manufacturing. Mater. Sci. Eng. A 2022, 830, 142327. [Google Scholar] [CrossRef]
  157. Shen, Q.; Xue, J.; Zheng, Z.; Yu, X.; Ou, N. Effect of thermal cycling on the microstructure and mechanical properties of AlCoCrFeNi2.1 high-entropy alloy fabricated using powder plasma arc additive manufacturing. Mater Lett. 2022, 325, 132902. [Google Scholar] [CrossRef]
  158. Vikram, R.; Murty, B.; Fabijanic, D.; Suwas, S. Insights into micro-mechanical response and texture of the additively manufactured eutectic high entropy alloy AlCoCrFeNi2.1. J. Alloy. Compd. 2020, 827, 154034. [Google Scholar] [CrossRef]
  159. Gwalani, B.; Soni, V.; Waseem, O.A.; Mantri, S.A.; Banerjee, R. Laser additive manufacturing of compositionally graded AlCrFeMoVx (x = 0 to 1) high-entropy alloy system. Opt. Laser Technol. 2019, 113, 330–337. [Google Scholar] [CrossRef]
  160. Gao, X.; Yu, Z.; Hu, W.; Lu, Y.; Zhu, Z.; Ji, Y.; Lu, Y.; Qin, Z.; Lu, X. In situ strengthening of CrMnFeCoNi high-entropy alloy with Al realized by laser additive manufacturing. J. Alloy. Compd. 2020, 847, 156563. [Google Scholar] [CrossRef]
  161. Malatji, N.; Popoola, A.; Lengopeng, T.; Pityana, S. Tribological and corrosion properties of laser additive manufactured AlCrFeNiCu high entropy alloy. Mater. Today: Proc. 2020, 28, 944–948. [Google Scholar] [CrossRef]
  162. Dada, M.; Popoola, P.; Aramide, O.; Mathe, N.; Pityana, S. Optimization of the corrosion property of a high entropy alloy using response surface methodology. Mater. Today Proc. 2020, 38, 1024–1030. [Google Scholar] [CrossRef]
  163. Nartu, M.; Chesetti, A.; Dasari, S.; Sharma, A.; Mantri, S.; Dahotre, N.; Banerjee, R. Engineering heterogeneous microstructures in additively manufactured high entropy alloys for high strength and strain hardenability. Mater. Sci. Eng. A 2022, 849, 143505. [Google Scholar] [CrossRef]
  164. Dada, M.; Popoola, P.; Mathe, N.; Pityana, S.; Adeosun, S. Effect of laser parameters on the properties of high entropy alloys: A preliminary study. Mater. Today Proc. 2020, 38, 756–761. [Google Scholar] [CrossRef]
  165. Dada, M.; Popoola, P.; Mathe, N.; Pityana, S.; Adeosun, S.; Aramide, O. The comparative study of the microstructural and corrosion behaviour of laser-deposited high entropy alloys. J. Alloy. Compd. 2021, 866, 158777. [Google Scholar] [CrossRef]
  166. Dada, M.; Popoola, P.; Mathe, N.; Pityana, S.; Adeosun, S.; Aramide, O.; Lengopeng, T. Process optimization of high entropy alloys by laser additive manufacturing. Eng. Rep. 2021, 2, e12252. [Google Scholar] [CrossRef]
  167. Liu, S.; Wan, D.; Guan, S.; Fu, Y.; Ren, X.; Zhang, Z.; He, J. Microstructure and nanomechanical behavior of an additively manufactured (CrCoNiFe)94Ti2Al4 high-entropy alloy. Mater. Sci. Eng. A 2021, 823, 141737. [Google Scholar] [CrossRef]
  168. Chew, Y.; Bi, G.; Zhu, Z.; Ng, F.; Weng, F.; Liu, S.; Nai, S.; Lee, B. Microstructure and enhanced strength of laser aided additive manufactured CoCrFeNiMn high entropy alloy. Mater. Sci. Eng. A 2018, 744, 137–144. [Google Scholar] [CrossRef]
  169. Guan, S.; Wan, D.; Solberg, K.; Berto, F.; Welo, T.; Yue, T.; Chan, K. Additive manufacturing of fine-grained and dislocation-populated CrMnFeCoNi high entropy alloy by laser engineered net shaping. Mater. Sci. Eng. A 2019, 761, 138056. [Google Scholar] [CrossRef]
  170. Gao, X.; Lu, Y. Laser 3D printing of CoCrFeMnNi high-entropy alloy. Mater. Lett. 2018, 236, 77–80. [Google Scholar] [CrossRef]
  171. Qiu, Z.; Yao, C.; Feng, K.; Li, Z.; Chu, P.K. Cryogenic deformation mechanism of CrMnFeCoNi high-entropy alloy fabricated by laser additive manufacturing process. Int. J. Light. Mater. Manuf. 2018, 1, 33–39. [Google Scholar] [CrossRef]
  172. Xiang, S.; Luan, H.; Wu, J.; Yao, K.-F.; Li, J.; Liu, X.; Tian, Y.; Mao, W.; Bai, H.; Le, G.; et al. Microstructures and mechanical properties of CrMnFeCoNi high entropy alloys fabricated using laser metal deposition technique. J. Alloy. Compd. 2018, 773, 387–392. [Google Scholar] [CrossRef]
  173. Tong, Z.; Ren, X.; Jiao, J.; Zhou, W.; Ren, Y.; Ye, Y.; Larson, E.A.; Gu, J. Laser additive manufacturing of FeCrCoMnNi high-entropy alloy: Effect of heat treatment on microstructure, residual stress and mechanical property. J. Alloy. Compd. 2019, 785, 1144–1159. [Google Scholar] [CrossRef]
  174. Melia, M.A.; Carroll, J.D.; Whetten, S.R.; Esmaeely, S.N.; Locke, J.; White, E.; Anderson, I.; Chandross, M.; Michael, J.R.; Argibay, N.; et al. Mechanical and Corrosion Properties of Additively Manufactured CoCrFeMnNi High Entropy Alloy. Addit. Manuf. 2019, 29, 100833. [Google Scholar] [CrossRef]
  175. Li, H.; Huang, Y.; Zhao, W.; Chen, T.; Sun, J.; Wei, D.; Du, Q.; Zou, Y.; Lu, Y.; Zhu, P.; et al. Overcoming the strength-ductility trade-off in an additively manufactured CoCrFeMnNi high entropy alloy via deep cryogenic treatment. Addit. Manuf. 2021, 50, 102546. [Google Scholar] [CrossRef]
  176. Zheng, M.; Li, C.; Zhang, X.; Ye, Z.; Yang, X.; Gu, J. The influence of columnar to equiaxed transition on deformation behavior of FeCoCrNiMn high entropy alloy fabricated by laser-based directed energy deposition. Addit. Manuf. 2020, 37, 101660. [Google Scholar] [CrossRef]
  177. Shittu, J.; Sadeghilaridjani, M.; Pole, M.; Muskeri, S.; Ren, J.; Liu, Y.; Tahoun, I.; Arora, H.; Chen, W.; Dahotre, N.; et al. Tribo-corrosion response of additively manufactured high-entropy alloy. npj Mater. Degrad. 2021, 5, 31. [Google Scholar] [CrossRef]
  178. Cui, Z.; Mi, Y.; Qiu, D.; Dong, P.; Qin, Z.; Gong, D.; Li, W. Microstructure and mechanical properties of additively manufactured CrMnFeCoNi high-entropy alloys after ultrasonic surface rolling process. J. Alloy. Compd. 2021, 887, 161393. [Google Scholar] [CrossRef]
  179. Li, H.; Huang, Y.; Jiang, S.; Lu, Y.; Gao, X.; Lu, X.; Ning, Z.; Sun, J. Columnar to equiaxed transition in additively manufactured CoCrFeMnNi high entropy alloy. Mater. Des. 2020, 197, 109262. [Google Scholar] [CrossRef]
  180. Bai, Y.; Jiang, H.; Yan, K.; Li, M.; Wei, Y.; Zhang, K.; Wei, B. Phase transition and heterogeneous strengthening mechanism in CoCrFeNiMn high-entropy alloy fabricated by laser-engineered net shaping via annealing at intermediate-temperature. J. Mater. Sci. Technol. 2021, 92, 129–137. [Google Scholar] [CrossRef]
  181. Li, H.; Fu, W.; Chen, T.; Huang, Y.; Ning, Z.; Sun, J.; Bai, H.; Dai, X.; Fan, H.; Ngan, A.H. Toward tunable microstructure and mechanical properties in additively manufactured CoCrFeMnNi high entropy alloy. J. Alloy. Compd. 2022, 924, 166513. [Google Scholar] [CrossRef]
  182. Wang, J.; Zhang, M.; Wang, H.; Li, Z.; Cheng, X.; Zhang, B.; Li, J.; Ran, X. Mitigating hot-cracking of laser melted CoCrFeNiMnTix high-entropy alloys. Mater. Lett. 2022, 314, 131771. [Google Scholar] [CrossRef]
  183. Haase, C.; Tang, F.; Wilms, M.B.; Weisheit, A.; Hallstedt, B. Combining thermodynamic modeling and 3D printing of elemental powder blends for high-throughput investigation of high-entropy alloys—Towards rapid alloy screening and design. Mater. Sci. Eng. A 2017, 688, 180–189. [Google Scholar] [CrossRef]
  184. Sui, Q.; Wang, Z.; Wang, J.; Xu, S.; Liu, B.; Yuan, Q.; Zhao, F.; Gong, L.; Liu, J. Additive manufacturing of CoCrFeNiMo eutectic high entropy alloy: Microstructure and mechanical properties. J. Alloy. Compd. 2022, 913, 165239. [Google Scholar] [CrossRef]
  185. Lu, H.; Zhang, X.; Liu, J.; Zhao, S.; Lin, X.; Li, H.; Hu, Y. Study on laser shock modulation of melt pool in laser additive manufacturing of FeCoCrNi high-entropy alloys. J. Alloy. Compd. 2022, 925, 166720. [Google Scholar] [CrossRef]
  186. Shen, Q.; Xue, J.; Yu, X.; Zheng, Z.; Ou, N. Powder plasma arc additive manufacturing of CoCrFeNiWx high-entropy alloys: Microstructure evolution and mechanical properties. J. Alloy. Compd. 2022, 922, 166245. [Google Scholar] [CrossRef]
  187. Wang, Q.; Amar, A.; Jiang, C.; Luan, H.; Zhao, S.; Zhang, H.; Le, G.; Liu, X.; Wang, X.; Yang, X.; et al. CoCrFeNiMo0.2 high entropy alloy by laser melting deposition: Prospective material for low temperature and corrosion resistant applications. Intermetallics 2020, 119, 106727. [Google Scholar] [CrossRef]
  188. Zhou, K.; Wang, Z.; He, F.; Liu, S.; Li, J.; Kai, J.-J.; Wang, J. A precipitation-strengthened high-entropy alloy for additive manufacturing. Addit. Manuf. 2020, 35, 101410. [Google Scholar] [CrossRef]
  189. Zhang, Y.; Chen, X.; Jayalakshmi, S.; Singh, R.A.; Konovalov, S.; Wang, Y. Replacement of Ta with equi-atomic radius Nb atoms in CoCrFeNiTa high entropy alloys: Effect on microstructure and mechanical properties. Mater. Lett. 2021, 297, 129966. [Google Scholar] [CrossRef]
  190. Liu, S.; Grohol, C.M.; Shin, Y.C. High throughput synthesis of CoCrFeNiTi high entropy alloys via directed energy deposition. J. Alloy. Compd. 2022, 916, 165469. [Google Scholar] [CrossRef]
  191. Kunce, I.; Polanski, M.; Bystrzycki, J. Microstructure and hydrogen storage properties of a TiZrNbMoV high entropy alloy synthesized using Laser Engineered Net Shaping (LENS). Int. J. Hydrogen Energy 2014, 39, 9904–9910. [Google Scholar] [CrossRef]
  192. Dobbelstein, H.; Gurevich, E.L.; George, E.P.; Ostendorf, A.; Laplanche, G. Laser metal deposition of a refractory TiZrNbHfTa high-entropy alloy. Addit. Manuf. 2018, 24, 386–390. [Google Scholar] [CrossRef]
  193. Dobbelstein, H.; Gurevich, E.L.; George, E.P.; Ostendorf, A.; Laplanche, G. Laser metal deposition of compositionally graded TiZrNbTa refractory high-entropy alloys using elemental powder blends. Addit. Manuf. 2019, 25, 252–262. [Google Scholar] [CrossRef]
  194. Dobbelstein, H.; Thiele, M.; Gurevich, E.L.; George, E.P.; Ostendorf, A. Direct Metal Deposition of Refractory High Entropy Alloy MoNbTaW. Phys. Procedia 2016, 83, 624–633. [Google Scholar] [CrossRef] [Green Version]
  195. Melia, M.A.; Whetten, S.R.; Puckett, R.; Jones, M.; Heiden, M.J.; Argibay, N.; Kustas, A.B. High-throughput additive manufacturing and characterization of refractory high entropy alloys. Appl. Mater. Today 2020, 19, 100560. [Google Scholar] [CrossRef]
  196. Moorehead, M.; Bertsch, K.; Niezgoda, M.; Parkin, C.; Elbakhshwan, M.; Sridharan, K.; Zhang, C.; Thoma, D.; Couet, A. High-throughput synthesis of Mo-Nb-Ta-W high-entropy alloys via additive manufacturing. Mater. Des. 2020, 18, 108358. [Google Scholar] [CrossRef]
  197. Lang, E.; Burns, K.; Wang, Y.; Kotula, P.G.; Kustas, A.B.; Rodriguez, S.; Aitkaliyeva, A.; Hattar, K. Compositional Effects of Additively Manufactured Refractory High-Entropy Alloys under High-Energy Helium Irradiation. Nanomaterials 2022, 12, 2014. [Google Scholar] [CrossRef]
  198. Busachi, A.; Erkoyuncu, J.; Colegrove, P.; Martina, F.; Ding, J. Designing a WAAM Based Manufacturing System for Defence Applications. Procedia CIRP 2015, 37, 48–53. [Google Scholar] [CrossRef] [Green Version]
  199. Busachi, A.; Erkoyuncu, J.; Colegrove, P.; Martina, F.; Watts, C.; Drake, R. A review of Additive Manufacturing technology and Cost Estimation techniques for the defence sector. CIRP J. Manuf. Sci. Technol. 2017, 19, 117–128. [Google Scholar] [CrossRef] [Green Version]
  200. Ahsan, M.; Seo, G.-J.; Fan, X.; Liaw, P.K.; Motaman, S.; Haase, C.; Kim, D.B. Effects of process parameters on bead shape, microstructure, and mechanical properties in wire + arc additive manufacturing of Al0.1CoCrFeNi high-entropy alloy. J. Manuf. Process. 2021, 68, 1314–1327. [Google Scholar] [CrossRef]
  201. Shen, Q.; Kong, X.; Chen, X. Fabrication of bulk Al-Co-Cr-Fe-Ni high-entropy alloy using combined cable wire arc additive manufacturing (CCW-AAM): Microstructure and mechanical properties. J. Mater. Sci. Technol. 2020, 74, 136–142. [Google Scholar] [CrossRef]
  202. Osintsev, K.; Konovalov, S.; Zaguliaev, D.; Ivanov, Y.; Gromov, V.; Panchenko, I. Investigation of Co-Cr-Fe-Mn-Ni Non-Equiatomic High-Entropy Alloy Fabricated by Wire Arc Additive Manufacturing. Metals 2022, 12, 197. [Google Scholar] [CrossRef]
  203. Gromov, V.; Konovalov, S.; Ivanov, Y.; Shliarova, Y.; Vorobyov, S.; Semin, A. Structure and properties of the CrMnFeCoNi high-entropy alloy irradiated with a pulsed electron beam. J. Mater. Res. Technol. 2022, 19, 4258–4269. [Google Scholar] [CrossRef]
  204. Shen, Q.; Kong, X.; Chen, X. Significant transitions of microstructure and mechanical properties in additively manufactured Al–Co–Cr–Fe–Ni high-entropy alloy under heat treatment. Mater. Sci. Eng. A 2021, 815, 141257. [Google Scholar] [CrossRef]
  205. Yao, X.; Peng, K.; Chen, X.; Jiang, F.; Wang, K.; Wang, Q. Microstructure and Mechanical Properties of Dual Wire-Arc Additive Manufactured Al-Co-Cr-Fe-Ni High Entropy Alloy. Mater. Lett. 2022, 326, 132928. [Google Scholar] [CrossRef]
  206. Gromov, V.; Ivanov, Y.; Konovalov, S.; Osintsev, K.; Semin, A.; Rubannikova, Y. Modification of high-entropy alloy AlCoCrFeNi by electron beam treatment. J. Mater. Res. Technol. 2021, 13, 787–797. [Google Scholar] [CrossRef]
  207. Osintsev, K.; Gromov, V.; Ivanov, Y.; Konovalov, S.; Panchenko, I.; Vorobyev, S. Evolution of Structure in AlCoCrFeNi High-Entropy Alloy Irradiated by a Pulsed Electron Beam. Metals 2021, 11, 1228. [Google Scholar] [CrossRef]
  208. Osintsev, K.; Konovalov, S.; Gromov, V.; Panchenko, I.; Ivanov, Y. Microstructural and mechanical characterisation of non-equiatomic Al2.1Co0.3Cr0.5FeNi2.1 high-entropy alloy fabricated via wire-arc additive manufacturing. Philos. Mag. Lett. 2021, 101, 353–359. [Google Scholar] [CrossRef]
  209. Osintsev, K.A.; Konovalov, S.V.; Gromov, V.E.; Ivanov, Y.F.; Panchenko, I.A. Microstructure and mechanical properties of non-equiatomic Co25.4Cr15Fe37.9Mn3.5Ni16.8Si1.4 high-entropy alloy produced by wire-arc additive manufacturing. Mater Lett. 2022, 312, 131675. [Google Scholar] [CrossRef]
  210. Liu, J.; Li, J.; Du, X.; Tong, Y.; Wang, R.; He, D.; Cai, Z.; Wang, H. Microstructure and Mechanical Properties of Wire Arc Additively Manufactured MoNbTaWTi High Entropy Alloys. Materials 2021, 14, 4512. [Google Scholar] [CrossRef]
  211. Ziaee, M.; Crane, N.B. Binder jetting: A review of process, materials, and methods. Addit. Manuf. 2019, 28, 781–801. [Google Scholar] [CrossRef]
  212. Karlsson, D.; Lindwall, G.; Lundbäck, A.; Amnebrink, M.; Boström, M.; Riekehr, L.; Schuisky, M.; Sahlberg, M.; Jansson, U. Binder jetting of the AlCoCrFeNi alloy. Addit. Manuf. 2019, 27, 72–79. [Google Scholar] [CrossRef]
  213. Xu, Z.; Zhu, Z.; Wang, P.; Meenashisundaram, G.K.; Nai, S.M.L.; Wei, J. Fabrication of porous CoCrFeMnNi high entropy alloy using binder jetting additive manufacturing. Addit. Manuf. 2020, 35, 101441. [Google Scholar] [CrossRef]
  214. Gonzalez-Gutierrez, J.; Cano, S.; Schuschnigg, S.; Kukla, C.; Sapkota, J.; Holzer, C. Additive Manufacturing of Metallic and Ceramic Components by the Material Extrusion of Highly-Filled Polymers: A Review and Future Perspectives. Materials 2018, 11, 840. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  215. Kenel, C.; Casati, N.P.M.; Dunand, D.C. 3D ink-extrusion additive manufacturing of CoCrFeNi high-entropy alloy micro-lattices. Nat. Commun. 2019, 10, 1–8. [Google Scholar] [CrossRef] [Green Version]
  216. Peng, S.; Mooraj, S.; Feng, R.; Liu, L.; Ren, J.; Liu, Y.; Kong, F.; Xiao, Z.; Zhu, C.; Liaw, P.K.; et al. Additive manufacturing of three-dimensional (3D)-architected CoCrFeNiMn high- entropy alloy with great energy absorption. Scr. Mater. 2020, 190, 46–51. [Google Scholar] [CrossRef]
  217. Kaczmar, J.; Pietrzak, K.; Włosiński, W. The production and application of metal matrix composite materials. J. Mater. Process. Technol. 2000, 106, 58–67. [Google Scholar] [CrossRef]
  218. Chen, H.; Lu, T.; Wang, Y.; Liu, Y.; Shi, T.; Prashanth, K.G.; Kosiba, K. Laser additive manufacturing of nano-TiC particles reinforced CoCrFeMnNi high-entropy alloy matrix composites with high strength and ductility. Mater. Sci. Eng. A 2022, 833, 142512. [Google Scholar] [CrossRef]
  219. Ng, C.K.; Bai, K.; Wuu, D.; Lau, K.B.; Lee, J.J.; Cheong, A.K.H.; Wei, F.; Cheng, B.; Wang, P.; Tan, D.C.C.; et al. Additive manufacturing of high-strength and ductile high entropy alloy CoCrFeNiW0.2 composites via laser powder bed fusion and post-annealing. J. Alloy. Compd. 2022, 906, 164288. [Google Scholar] [CrossRef]
  220. Guan, S.; Wan, D.; Solberg, K.; Berto, F.; Welo, T.; Yue, T.; Chan, K. Additively manufactured CrMnFeCoNi/AlCoCrFeNiTi0.5 laminated high-entropy alloy with enhanced strength-plasticity synergy. Scr. Mater. 2020, 183, 133–138. [Google Scholar] [CrossRef]
  221. Li, B.; Qian, B.; Xu, Y.; Liu, Z.; Xuan, F. Fine-structured CoCrFeNiMn high-entropy alloy matrix composite with 12 wt% TiN particle reinforcements via selective laser melting assisted additive manufacturing. Mater. Lett. 2019, 252, 88–91. [Google Scholar] [CrossRef]
  222. Li, B.; Zhang, L.; Xu, Y.; Liu, Z.; Qian, B.; Xuan, F. Selective laser melting of CoCrFeNiMn high entropy alloy powder modified with nano-TiN particles for additive manufacturing and strength enhancement: Process, particle behavior and effects. Powder Technol. 2019, 360, 509–521. [Google Scholar] [CrossRef]
  223. Lu, T.; Yao, N.; Chen, H.; Sun, B.; Chen, X.; Scudino, S.; Kosiba, K.; Zhang, X. Exceptional strength-ductility combination of additively manufactured high-entropy alloy matrix composites reinforced with TiC nanoparticles at room and cryogenic temperatures. Addit. Manuf. 2022, 56, 102918. [Google Scholar] [CrossRef]
  224. Amar, A.; Li, J.; Xiang, S.; Liu, X.; Zhou, Y.; Le, G.; Wang, X.; Qu, F.; Ma, S.; Dong, W.; et al. Additive manufacturing of high-strength CrMnFeCoNi-based High Entropy Alloys with TiC addition. Intermetallics 2019, 109, 162–166. [Google Scholar] [CrossRef]
  225. Zhang, X.; Li, R.; Huang, L.; Amar, A.; Wu, C.; Le, G.; Liu, X.; Guan, D.; Yang, G.; Li, J. Influence of in-situ and ex-situ precipitations on microstructure and mechanical properties of additive manufacturing CoCrFeMnNi high-entropy alloys. Vacuum 2021, 187, 110111. [Google Scholar] [CrossRef]
  226. Li, J.; Xiang, S.; Luan, H.; Amar, A.; Liu, X.; Lu, S.; Zeng, Y.; Le, G.; Wang, X.; Qu, F.; et al. Additive manufacturing of high-strength CrMnFeCoNi high-entropy alloys-based composites with WC addition. J. Mater. Sci. Technol. 2019, 35, 2430–2434. [Google Scholar] [CrossRef]
  227. Wang, Y.; Zhao, L.; Wan, D.; Guan, S.; Chan, K. Additive manufacturing of TiB2-containing CoCrFeMnNi high-entropy alloy matrix composites with high density and enhanced mechanical properties. Mater. Sci. Eng. A 2021, 825, 141871. [Google Scholar] [CrossRef]
  228. Pegues, J.W.; Melia, M.A.; Rodriguez, M.A.; Babuska, T.F.; Gould, B.; Argibay, N.; Greco, A.; Kustas, A.B. In situ synchrotron X-ray imaging and mechanical properties characterization of additively manufactured high-entropy alloy composites. J. Alloy. Compd. 2021, 876, 159505. [Google Scholar] [CrossRef]
  229. Shen, Q.; Kong, X.; Chen, X.; Yao, X.; Deev, V.B.; Prusov, E.S. Powder plasma arc additive manufactured CoCrFeNi(SiC)x high-entropy alloys: Microstructure and mechanical properties. Mater Lett. 2021, 282, 128736. [Google Scholar] [CrossRef]
  230. Thapliyal, S.; Agrawal, P.; Agrawal, P.; Nene, S.S.; Mishra, R.S.; McWilliams, B.A.; Cho, K.C. Segregation engineering of grain boundaries of a metastable Fe-Mn-Co-Cr-Si high entropy alloy with laser-powder bed fusion additive manufacturing. Acta Mater. 2021, 219, 117271. [Google Scholar] [CrossRef]
  231. Xu, J.; Duan, R.; Feng, K.; Zhang, C.; Zhou, Q.; Liu, P.; Li, Z. Enhanced strength and ductility of laser powder bed fused NbMoTaW refractory high-entropy alloy via carbon microalloying. Addit. Manuf. Lett. 2022, 3, 100079. [Google Scholar] [CrossRef]
  232. Yang, Y.; Hu, J.; Liu, X.; Xu, W.; Li, B.; Ling, G.; Pang, X.; Tian, Y. Post treatment of an additively manufactured composite consisting of 304 L stainless steel and CoCrFeMnNi high-entropy alloy. Mater. Sci. Eng. A 2021, 831, 142104. [Google Scholar] [CrossRef]
  233. Cai, Y.; Zhu, L.; Cui, Y.; Han, J. Manufacturing of FeCoCrNi + FeCoCrNiAl laminated high-entropy alloy by laser melting deposition (LMD). Mater. Lett. 2021, 289, 129445. [Google Scholar] [CrossRef]
  234. Chen, J.; Yao, Z.; Wang, X.; Lu, Y.; Wang, X.; Liu, Y.; Fan, X. Effect of C content on microstructure and tensile properties of as-cast CoCrFeMnNi high entropy alloy. Mater. Chem. Phys. 2018, 210, 136–145. [Google Scholar] [CrossRef]
  235. Lei, Z.; Liu, X.; Wu, Y.; Wang, H.; Jiang, S.; Wang, S.; Hui, X.; Wu, Y.; Gault, B.; Kontis, P.; et al. Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes. Nature 2018, 563, 546–550. [Google Scholar] [CrossRef] [PubMed]
  236. Song, M.; Zhou, R.; Gu, J.; Wang, Z.; Ni, S.; Liu, Y. Nitrogen induced heterogeneous structures overcome strength-ductility trade-off in an additively manufactured high-entropy alloy. Appl. Mater. Today 2019, 18, 100498. [Google Scholar] [CrossRef]
  237. Wang, Z.; Gu, J.; An, D.; Liu, Y.; Song, M. Characterization of the microstructure and deformation substructure evolution in a hierarchal high-entropy alloy by correlative EBSD and ECCI. Intermetallics 2020, 121, 106788. [Google Scholar] [CrossRef]
  238. Zhou, R.; Liu, Y.; Zhou, C.; Li, S.; Wu, W.; Song, M.; Liu, B.; Liang, X.; Liaw, P. Microstructures and mechanical properties of C-containing FeCoCrNi high-entropy alloy fabricated by selective laser melting. Intermetallics 2018, 94, 165–171. [Google Scholar] [CrossRef]
  239. Zhou, R.; Liu, Y.; Liu, B.; Li, J.; Fang, Q. Precipitation behavior of selective laser melted FeCoCrNiC0.05 high entropy alloy. Intermetallics 2019, 106, 20–25. [Google Scholar] [CrossRef]
  240. Wu, W.; Zhou, R.; Wei, B.; Ni, S.; Liu, Y.; Song, M. Nanosized precipitates and dislocation networks reinforced C-containing CoCrFeNi high-entropy alloy fabricated by selective laser melting. Mater. Charact. 2018, 144, 605–610. [Google Scholar] [CrossRef]
  241. Zhu, Z.G.; An, X.H.; Lu, W.J.; Li, Z.M.; Ng, F.L.; Liao, X.Z.; Ramamurty, U.; Nai, S.M.L.; Wei, J. Selective laser melting enabling the hierarchically heterogeneous microstructure and excellent mechanical properties in an interstitial solute strengthened high entropy alloy. Mater. Res. Lett. 2019, 7, 453–459. [Google Scholar] [CrossRef] [Green Version]
  242. Park, J.M.; Choe, J.; Kim, J.G.; Bae, J.W.; Moon, J.; Yang, S.; Kim, K.T.; Yu, J.; Kim, H.S. Superior tensile properties of 1% C-CoCrFeMnNi high-entropy alloy additively manufactured by selective laser melting. Mater. Res. Lett. 2020, 8, 1–7. [Google Scholar] [CrossRef] [Green Version]
  243. Park, J.M.; Choe, J.; Park, H.K.; Son, S.; Jung, J.; Kim, T.-S.; Yu, J.-H.; Kim, J.G.; Kim, H.S. Synergetic strengthening of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy by heterogeneous anisotropic microstructure. Addit. Manuf. 2020, 35, 101333. [Google Scholar] [CrossRef]
  244. Zhao, D.; Yang, Q.; Wang, D.; Yan, M.; Wang, P.; Jiang, M.; Liu, C.; Diao, D.; Lao, C.; Chen, Z.; et al. Ordered nitrogen complexes overcoming strength–ductility trade-off in an additively manufactured high-entropy alloy. Virtual Phys. Prototyp. 2020, 15, 532–542. [Google Scholar] [CrossRef]
  245. Guo, L.; Gu, J.; Gan, B.; Ni, S.; Bi, Z.; Wang, Z.; Song, M. Effects of elemental segregation and scanning strategy on the mechanical properties and hot cracking of a selective laser melted FeCoCrNiMn-(N,Si) high entropy alloy. J. Alloys Compd. 2021, 865, 158892. [Google Scholar] [CrossRef]
  246. 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, 5743–5755. [Google Scholar] [CrossRef] [Green Version]
  247. Gwalani, B.; Soni, V.; Lee, M.; Mantri, S.A.; Ren, Y.; Banerjee, R. Optimizing the coupled effects of Hall-Petch and precipitation strengthening in a Al0.3CoCrFeNi high entropy alloy. Mater Des. 2017, 121, 254–260. [Google Scholar] [CrossRef]
  248. Ma, S.G.; Zhang, S.F.; Qiao, J.W.; Wang, Z.H.; Gao, M.C.; Jiao, Z.M.; Yang, H.J.; Zhang, Y. Superior high tensile elongation of a single-crystal CoCrFeNiAl0.3 high-entropy alloy by Bridgman solidification. Intermetallics 2014, 54, 104–109. [Google Scholar] [CrossRef]
Materials 16 02454 g001 550
Figure 1. Crystal structure of a conventional alloy vs. high entropy alloys (HEAs).
Figure 1. Crystal structure of a conventional alloy vs. high entropy alloys (HEAs).
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Figure 2. Main types of additive manufacturing (AM) processes according to ASTM F2792—12a.
Figure 2. Main types of additive manufacturing (AM) processes according to ASTM F2792—12a.
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Figure 3. Number of publications on AM of HEAs using direct energy deposition (DED), powder bed fusion (PBF), binder jetting (BJ), and material extrusion (ME) technologies.
Figure 3. Number of publications on AM of HEAs using direct energy deposition (DED), powder bed fusion (PBF), binder jetting (BJ), and material extrusion (ME) technologies.
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Figure 4. Common alloying elements for HEAs along with number of publications that relate to various combinations of chemical composition.
Figure 4. Common alloying elements for HEAs along with number of publications that relate to various combinations of chemical composition.
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Materials 16 02454 g005 550
Figure 5. Number of publications related to AM of HEAs using pre-alloyed powder and mix elemental powder by various printing processes.
Figure 5. Number of publications related to AM of HEAs using pre-alloyed powder and mix elemental powder by various printing processes.
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Materials 16 02454 g006 550
Figure 6. Schematic illustration of typical PBF process.
Figure 6. Schematic illustration of typical PBF process.
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Materials 16 02454 g007 550
Figure 7. Schematic illustration of the typical microstructure of AlCrFeCoNi and AlFeCoNiCu produced by EB-PBF, showing the formation of FCC phase at grain boundaries due to elemental segregation during the pre-heating process.
Figure 7. Schematic illustration of the typical microstructure of AlCrFeCoNi and AlFeCoNiCu produced by EB-PBF, showing the formation of FCC phase at grain boundaries due to elemental segregation during the pre-heating process.
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Materials 16 02454 g008 550
Figure 8. Density of CrFeCoNi HEA using both mix elemental and pre-alloyed powders vs. different volume laser energy by Hou et al. [120].
Figure 8. Density of CrFeCoNi HEA using both mix elemental and pre-alloyed powders vs. different volume laser energy by Hou et al. [120].
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Materials 16 02454 g009 550
Figure 9. Macroscopic structure by optical microscopy of HEA VNbMoTaW obtained by various LPBF trials using mix elemental powder: (a) LPBF—Primary trials, (b) LPBF—Intermediate trials, (c) LPBF—Advanced trials.
Figure 9. Macroscopic structure by optical microscopy of HEA VNbMoTaW obtained by various LPBF trials using mix elemental powder: (a) LPBF—Primary trials, (b) LPBF—Intermediate trials, (c) LPBF—Advanced trials.
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Materials 16 02454 g010 550
Figure 10. Schematic illustration of blown powder deposition (BFD) process.
Figure 10. Schematic illustration of blown powder deposition (BFD) process.
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Materials 16 02454 g011 550
Figure 11. Schematic illustration of the microstructure characteristics as a function of printing orientation of DED-produced parts.
Figure 11. Schematic illustration of the microstructure characteristics as a function of printing orientation of DED-produced parts.
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Materials 16 02454 g012 550
Figure 12. Schematic illustration of wire arc AM (WAAM) process.
Figure 12. Schematic illustration of wire arc AM (WAAM) process.
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Materials 16 02454 g013 550
Figure 13. Schematic illustration of CCWs composed with 5 different wires (A–E) for DED process.
Figure 13. Schematic illustration of CCWs composed with 5 different wires (A–E) for DED process.
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Materials 16 02454 g014 550
Figure 14. (a) SEM image of CCW composed from three stranded wires (pure Co wire, Autrod 16.95 welding wire and Ni80Cr20 wire, (b) photograph of the CCW wire [202].
Figure 14. (a) SEM image of CCW composed from three stranded wires (pure Co wire, Autrod 16.95 welding wire and Ni80Cr20 wire, (b) photograph of the CCW wire [202].
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Materials 16 02454 g015 550
Figure 15. Schematic illustration of BJ process.
Figure 15. Schematic illustration of BJ process.
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Materials 16 02454 g016 550
Figure 16. Schematic illustration of ME process using a plunger.
Figure 16. Schematic illustration of ME process using a plunger.
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Figure 17. Optical microscopy showing the relative density of three HEA compositions in low, optimal, and high VED (VED values presented in red), Farquhar et al. [101].
Figure 17. Optical microscopy showing the relative density of three HEA compositions in low, optimal, and high VED (VED values presented in red), Farquhar et al. [101].
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Figure 18. The effect of different AM technologies on tensile strength of CrMnFeCoNi HEA in terms of YS, UTS, and elongation. L-PBF [45,74,75,82,84,87,203], EB-PBF [115], L-DED [160,168,170,171,172,173,174,180], WAAM [202], AMF [87,172,246].
Figure 18. The effect of different AM technologies on tensile strength of CrMnFeCoNi HEA in terms of YS, UTS, and elongation. L-PBF [45,74,75,82,84,87,203], EB-PBF [115], L-DED [160,168,170,171,172,173,174,180], WAAM [202], AMF [87,172,246].
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Materials 16 02454 g019 550
Figure 19. The effect of different AM technologies on tensile strength of Al0.3CrFeCoNi HEA in terms of YS, UTS and elongation. L-PBF [53,105], L-DED [145,146], AMF [247,248].
Figure 19. The effect of different AM technologies on tensile strength of Al0.3CrFeCoNi HEA in terms of YS, UTS and elongation. L-PBF [53,105], L-DED [145,146], AMF [247,248].
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Table
Table 1. HEAs fabricated by L-PBF process and pre-alloyed powders as feedstock material.
Table 1. HEAs fabricated by L-PBF process and pre-alloyed powders as feedstock material.
AlloyCrystal StructureRef.
AlCrFeCoNiBCC/B2[50,51,52]
Al0.3CrFeCoNiFCC[53]
Al0.5CrFeCoNiFCC[54]
AlCrFeCoNi2.1FCC[55]
AlCrFeCoNi2.1FCC + BCC/B2[56,57,58,59]
AlCrFe2Ni2BCC/B2[48]
Al0.55Cr0.5FeNiBCC/B2[60]
AlCrFeNiCuBCC/B2[61]
AlCrFeNi2CuFCC + BCC/B2[62]
AlCrFeNi2.5CuFCC + BCC/B2[62]
AlCrFeNi2.75CuFCC + BCC/B2[62]
AlCrFeNi3CuFCC + BCC/B2[62]
Al0.3CrFeCoNiCuFCC[63]
AlFeCoNiCuFCC + BCC/B2[64]
CrFeCo1.1Ni1.6FCC + BCC[65]
CrFeCoNiFCC[47,66,67,68,69,70,71,72,73]
CrMnFeCoNiFCC[45,46,49,74,75,76,77,78,79,80,81,82,83,84,85,86,87]
TiMoTaWBCC + HCP[88]
Ti2.3Zr2.3NbMoTaBCC[89]
Al2CrFeCo3Ni3Mo0.1W0.1FCC + BCC/B2[90]
AlCrFeCoNiCuFCC + BCC/B2[91]
Al0.2Ti0.3CrFeCo1.5Ni1.5FCC[92]
Al0.3Ti0.23FeCoNiFCC[93]
Al0.25Ti0.25FeCoNiFCC[94]
Al0.5V0.2Cr0.9FeNi2.5FCC[95]
Si0.25Cr0.75MnFe2CoFCC + HCP[96]
Si0.25Cr0.75MnFe2CoCu2FCC + HCP[97]
Si0.25Cr0.75MnFe2CoFCC + HCP[98]
Ti0.5CrFeCo1.5Ni1.5Mo0.1FCC + HCP[99]
CrFeCoNiFCC[100]
CrFeCoNiFCC[101]
CrFeNi2CuFCC[102]
TiCr2.5FeCoNi2W0.5BCC[103]
TiCr4Fe9Ni6WFCC[104]
Table
Table 2. LPBF production of HEAs using a blend of pre-alloyed and pure element powders as feedstock material.
Table 2. LPBF production of HEAs using a blend of pre-alloyed and pure element powders as feedstock material.
AlloyFeedstock MaterialCrystal StructureRef.
AlCrFeCoNiPre-alloyed + AlBCC/B2[72]
Al0.01CrFeCoNiPre-alloyed + AlFCC[73]
Al0.05CrFeCoNiPre-alloyed + AlFCC[73]
Al0.1CrFeCoNiPre-alloyed + AlFCC[72,73]
Al0.3CrFeCoNiPre-alloyed + AlFCC + BCC/B2[105]
Al0.5CrFeCoNiPre-alloyed + AlFCC + BCC/B2[72]
Al0.5CrFeNi2CuPre-alloyed + AlFCC + BCC/B2[102]
Al0.75CrFeNi2CuPre-alloyed + AlFCC + BCC/B2[102]
AlCrFeNi2CuPre-alloyed + AlFCC + BCC/B2[102]
AlCrFeCoNi2.1Pre-alloyed + pre-alloyedFCC + BCC/B2[106]
AlCrFe2.3Ni2.3Pre-alloyed + Fe + NiFCC + BCC/B2[107]
CrMnFeCoNiPre-alloyed + MnFCC[108]
CrMnFeCoNiPre-alloyed + pre-alloyedFCC[109]
CrFeCoNiCuPre-alloyed + CuFCC[101]
Ti0.2CrFeCoNiPre-alloyed + TiFCC[100]
Ti0.4CrFeCoNiPre-alloyed + TiFCC[100]
Ti0.6CrFeCoNiPre-alloyed + TiFCC[100]
TiCrFeCoNiPre-alloyed + TiFCC + HCP + NiTi[101]
Table
Table 3. HEAs fabricated by EB-PBF process using pre-alloyed powders as feedstock material.
Table 3. HEAs fabricated by EB-PBF process using pre-alloyed powders as feedstock material.
AlloyCrystal StructureRef.
AlCrFeCoNiFCC + BCC/B2[110,111,112,114]
AlFeCoNiCuFCC + BCC/B2[113]
CrMnFeCoNiFCC[115,116,117]
CrMnFeCoNiTi0.18FCC + σ + γ + D024[117]
CrMnFeCoNiTi0.5BCC + σ + γ + D024[117]
CrMnFeCoNiTi2BCC + σ + γ + D024[117]
CrFeCoNiMoFCC + SC + Ni3Ti[118]
Table
Table 6. Fabrication of HEAs by DED process using wire as feedstock material.
Table 6. Fabrication of HEAs by DED process using wire as feedstock material.
AlloyAM SystemFeedstock MaterialCrystal StructureRef.
Al0.1CrFeCoNiArc weldingPre-alloyed WireFCC[200]
AlCrFeCoNiArc welding7 WiresFCC + BCC/B2[201,204,205]
Al0.7Cr0.4FeCo0.34Ni2Electron beam3 WiresSC[206,207]
Al2.1Cr0.5FeCo0.3Ni2.1Arc welding3 WiresBCC/B2[208]
CrMnFeCoNiArc welding3 WiresFCC[202]
CrMnFeCoNiElectron beam3 WiresFCC[203]
SiCrMnFeCoNiArc welding 3 WiresFCC[209]
TiNbMoTaWArc welding7 WiresBCC[210]
Table
Table 7. HEAs fabricated by BJ process and pre-alloyed powders.
Table 7. HEAs fabricated by BJ process and pre-alloyed powders.
AlloySintering TemperatureCrystal StructureRef.
AlCrFeCoNi900   ° C FCC + BCC/B2 + σ[212]
AlCrFeCoNi1000   ° C , 1100   ° C FCC + BCC/B2[212]
AlCrFeCoNi1200   ° C , 1300   ° C BCC/B2[212]
CrMnFeCoNi1150   ° C , 1250   ° C FCC[213]
Table
Table 8. HEAs fabricated by ME process.
Table 8. HEAs fabricated by ME process.
AlloyBinderFeedstock MaterialCrystal StructureRef.
CrFeCoNiPLGA + DBPElemental FCC[215]
CrMnFeCoNiTHF + 2-Butoxyethanol + PMMA-PnBA Pre-alloyedFCC[216]
Table
Table 9. Composite materials with HEA matrix.
Table 9. Composite materials with HEA matrix.
AlloyTypeAMRaw MaterialCrystal StructureRef.
CrMnFeCoNiReinforcing particlesL-PBFPre-alloyed + TiNFCC + TiN[221,222]
CrMnFeCoNiReinforcing particlesL-PBFPre-alloyed + nano TiCFCC[218,223]
CrMnFeCoNiReinforcing particlesL-DEDPre-alloyed + TiCFCC + TiC[224,225]
CrMnFeCoNiReinforcing particlesL-DEDPre-alloyed + WCFCC+M23C6[225,226]
CrMnFeCoNiReinforcing particlesL-DEDPre-alloyed + TiB2FCC + TiB2[227]
CrMnFeCoNiReinforcing particlesL-DEDPre-alloyed + WFCC + BCC + Fe7W6[228]
CrFeCoNiReinforcing particlesPA-DEDElemental + SiC FCC+Cr7C3[229]
CrFeCoNiReinforcing particlesL-PBFPre-alloyed + WFCC + W[219]
SiCrMnFeCoReinforcing particlesL-PBFPre-alloyed + B4CFCC+HCP[230]
NbMoTaWReinforcing particlesL-PBFPre-alloyed + W + WCBCC + NbC[231]
CrMnFeCoNi + 304 SSLaminated structureL-DEDPre-alloyed + 304SSFCC[232]
AlCrFeCoNi + CrFeCoNiLaminated structureL-DEDPre-alloyed FCC/BCC[233]
AlTi0.5CrFeCoNi + CrMnFeCoNiLaminated structureL-DEDPre-alloyed FCC/BCC[220]
Table
Table 10. Interstitial doping of HEAs fabricated by L-PBF process and pre-alloyed feedstock material.
Table 10. Interstitial doping of HEAs fabricated by L-PBF process and pre-alloyed feedstock material.
AlloyInterstitial DopingCrystal StructureRef.
CrFeCoNiNFCC[236,237]
CrFeCoNiCFCC[238,239,240]
CrMnFeCoCFCC + HCP[241]
CrMnFeCoNiCFCC[242,243]
CrMnFeCoNiNFCC[244,245]
Table
Table 11. Printing parameter of selected HEA compositions produced by different AM processes.
Table 11. Printing parameter of selected HEA compositions produced by different AM processes.
AlloyAM SystemFeedstock MaterialPowder Size [µm]Printing
Parameters		Ref.
Al0.1CrFeCoNiWAAMPre-alloyed WireXCurrent: 200 A
Voltage: 15.5 V
Travel speed: 3.3, 10 mm/s
Feed rate: 2000 mm/min
Energy density: 82.23, 120 J/mm3		[200]
Al0.3CrFeCoNiL-DEDPre-alloyed74–150
Average: 110		Power: 1000 w
Travel speed: 1000 mm/s
Layer thickness: 30 μm		[145]
Al0.3CrFeCoNiL-PBFPre-alloyed20–42
Average: 29		Power: 150–170 w
Scan speed: 1100–1300 mm/s
Layer thickness: 25–30 μm
Hatch spacing: 45 μm
Energy density: 85–137 J/mm3		[53]
AlCrFeCoNiL-PBFPre-alloyed3.8–53
Average: 28.6		Power: 250–400 w
Scan speed: 1000 mm/s
Layer thickness: 40 μm
Hatch spacing: 90 μm
Energy density: 68.4–111 J/mm3		[52]
AlCrFeCoNiEB-PBFPre-alloyed45–105Beam Current: 4.5–9 mA
Preheating temperature: 950   ° C
Scan speed: 215 mm/s
Layer thickness: 70 μm		[112]
AlCrFeCoNiL-DEDPre-alloyed75–150Power: 950 w
Travel speed: 4 mm/s
Feed rate: 9.5 g/min
Layer thickness: 30 μm		[135]
AlCrFeCoNiL-DEDElemental 50–150Power: 800 w
Travel speed: 13 mm/s
Layer thickness: 25 μm		[141]
AlCrFeCoNiWAAM7 WiresXCurrent: 156 A
Voltage: 16.2 V
Travel speed: 8–12 mm/s
Feed rate: 5.5 m/min		[201]
AlCrFeCoNi2.1L-PBFPre-alloyed + Ni10–75
Average: 32.7		Power: 200–400 w
Scan speed: 600–1000 mm/s
Energy density: 88.9–190 J/mm3		[56]
CrFeCoNiL-PBFElemental 19-73Power: 100–250 w
Scan speed: 700–1100 mm/s
Layer thickness: 20 μm
Hatch spacing: 80 μm
Energy density: 57–223 J/mm3		[120]
CrFeCoNiL-PBFPre-alloyed18–49
Average: 30.1		Power: 94 w
Scan speed: 582 mm/s
Layer thickness: 30 μm
Hatch spacing: 42 μm
Energy density: 128.2 J/mm3		[101]
CrMnFeCoNiL-PBFPre-alloyed5–45
Average: 36		Power: 400 w
Scan speed: 800–4000 mm/s
Layer thickness: 40 μm
Hatch spacing: 90 μm
Energy density: 37–185 J/mm3		[75]
CrMnFeCoNiL-PBFPre-alloyed20–80
Average: 43.4		Power: 150 w
scan speed: 600 mm/s
layer thickness: 60 μm
hatch spacing: 50 μm
Energy density: 83 J/mm3		[79]
CrMnFeCoNiEB-PBFPre-alloyed44.1–88.7
Average: 65		Current: 2–14 mA
Preheating temperature: 900–980   ° C
scan speed: 492–3446 mm/s
layer thickness: 50–70 μm
hatch spacing: 50–70 μm		[115]
CrMnFeCoNiL-DEDPre-alloyedAverage: 120Power: 1000–1400 w
Travel speed: 13 mm/s
feed rate: 7–9 g/min		[172]
CrMnFeCoNiL-DEDPre-alloyed10–90Power: 600–1000 w
Travel speed: 13 mm/s
feed rate: 7–9 g/min		[173]
Table
Table 12. Comparison of production characteristics and microstructure phenomena of different AM processes used to produce HEAs.
Table 12. Comparison of production characteristics and microstructure phenomena of different AM processes used to produce HEAs.
Production Characteristics and Microstructure PhenomenonPBFDEDBJME
Feedstock materialPowders
Pre-alloyed and
elemental		Powders and wires
Pre-alloyed and
elemental		Powder
Pre-alloyed 		Powder paste
Pre-alloyed
Powder sizeFew micronsNo limitationFew micronsNo limitation
Heat sourceLaser beam
Electron beam
Arc melting		Laser beam
Electron beam
Arc melting		No heat sourceNo heat source
Deposition rateLowHighHighHigh
Post-processing
requirements		Stress relief No requirementsSintering Sintering
Printing geometryComplexSimpleComplexSimple
AccuracyHighLowHighLow
Multi-material
Production ability		One materialMulti-material
ability 		One materialMulti-material
ability
Typical microstructure Preferred orientation (columnar /dendrite structure)
For EB-PBF increase in grain size in lower section of the part		Preferred orientation (columnar /dendrite structure)
Increase in grain size in lower section of the part		Relatively large equiaxed grain structureRelatively large equiaxed grain structure
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Ron, T.; Shirizly, A.; Aghion, E. Additive Manufacturing Technologies of High Entropy Alloys (HEA): Review and Prospects. Materials 2023, 16, 2454. https://doi.org/10.3390/ma16062454

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Ron T, Shirizly A, Aghion E. Additive Manufacturing Technologies of High Entropy Alloys (HEA): Review and Prospects. Materials. 2023; 16(6):2454. https://doi.org/10.3390/ma16062454

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Ron, Tomer, Amnon Shirizly, and Eli Aghion. 2023. "Additive Manufacturing Technologies of High Entropy Alloys (HEA): Review and Prospects" Materials 16, no. 6: 2454. https://doi.org/10.3390/ma16062454

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