Additive Manufacturing of High Entropy Alloys
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Alloying has been very common practice in materials engineering to fabricate metals of desirable properties for specific applications. Traditionally, a small amount of the desired material is added to the principal metal. However, a new alloying technique emerged in 2004 with the concept of adding several principal elements in or near equi-atomic concentrations. These are popularly known as high entropy alloys (HEAs) which can have a wide composition range.

  • high entropy alloys (HEAs)
  • additive manufacturing (AM)
  • wear
  • nuclear applications
  • irradiation

1. Introduction

1.1. The Definitions of High Entropy Alloys

The first ever definition of HEA was given by Yeh et al. [3] as a class of alloys composed of five or more principal elements having concentration between 5% to 35% for each element. The second definition was also proposed by the same group [13]. In the second definition, the three categories of alloys were introduced on the basis of the configurational entropy: low entropy alloys (configurational entropy alloys (ΔSconf) ≤ 0.69R), medium entropy alloys (0.69R ≤ ΔSconf ≤ 1.61R) and high entropy alloys (ΔSconf ≥ 1.61R) [30], where R is the universal gas constant. Here, the low entropy alloys are mostly conventional alloys with one or two major elements and the medium entropy alloys have two to four major elements. The high entropy alloys contain five or more major elements. The second definition does not require equi-atomic composition. For example, Ti2ZrHfV0.5Mo0.2 [80], FeCoNiCrTi0.2 [81] and Al0.1CoCrFeNi [82,83] are categorized as HEAs according to the second definition.
Moreover, these definitions are not strict, and it is not clarified which one should be used to categorize an alloy. For example, an alloy having composition of 5% A, 5% B, 20% C, 35% D and 35% E has the configuration entropy of 1.36R according to Equation (1) derived from Boltzmann’s entropy formula [30].
where cn is the atomic fraction of the nth element. In case of equi-atomic composition, Equation (1) reduces to [30]:
For example, an alloy having 25 components with equi-atomic concentration has ΔSconf = Rln(n = 25) = 3.22R. This material has the concentration of each element out of the range suggested by the first definition (between 5% to 35%), but it has sufficiently high entropy according to the second definition [15].

2. Manufacturing of HEAs

2.1. Background and Conventional Methods

Brian Cantor estimated the total number of possible metallic alloys with different compositions to be up to around 1078 [12]. This means many new alloys are yet to be discovered. For the manufacturing of HEAs, the initial synthesis strategy was to choose equi-atomic concentration of principle elements to maximize the entropy of the system. However, later, HEAs in non-equi-molar ratios were also developed for various applications. Arc melting was mostly preferred to produce HEAs thanks to its convenience, availability and simplicity. Furthermore, developing a HEA became more complex as more non-equi-atomic compositions were considered and several other manufacturing techniques were used. Alshataif et al. [84] covered almost all kinds of processing techniques used so far for HEAs synthesis. They detailed solid state processing (i.e., powder atomization methods, ball milling, cold/hot pressing, sintering, spark plasma sintering), liquid state processing (i.e., arc melting, vacuum induction melting, directional solidification, infiltration, electromagnetic stirring), thin film deposition (i.e., magnetron sputtering, pulsed laser deposition, plasma spray deposition) and additive manufacturing. Most of these manufacturing techniques are commercially available. That means most HEAs would not require a special manufacturing process and mass-producing HEAs would be possible with the existing alloying technologies and facilities.
The influence of process parameters, such as temperature and pressure, on the properties of HEAs were also studied. The effects of temperature on the properties of HEAs were studied through processes such as: annealing and heat treatments [85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104] and thermomechanical processing [105,106,107,108]. A number of research groups reported how temperature affected the microstructures and mechanical properties of HEAs in various manufacturing processes [96,109,110,111,112]. Moreover, the physical or chemical responses of various HEAs under a variety of thermal histories during manufacturing were studied: thermal aging behavior [86,113,114,115], TaNbHfZrTi synthesis by hydrogenation–dehydrogenation reaction and thermal plasma treatment [116], martensite formation [117,118,119,120], AlxCoCrFeNi formation with high gravity combustion from oxides [121], laser surface melting [122], precipitation behavior [123,124,125,126] and WTaMoNbV synthesis using inductively coupled thermal plasma [127].
Researchers have also attempted to alter the microstructures and properties of HEAs by high pressure treatments. Regulating pressure during fabrication of HEAs can considerably alter the interaction between the atoms by changing the interatomic distance, bonding nature and packing densities. These changes often convert the microstructures and affect the mechanical and structural properties. Dong et al. [56] reviewed the applications of high pressure technology for HEAs. They reviewed the use of dynamic high pressure, diamond anvil cells, high pressure torsion and hexahedron anvil press. Zhang et al. [128] reviewed high pressure induced phase transitions in HEAs. Application of high pressure torsion [37,129,130,131,132,133,134,135,136,137,138,139,140,141,142] is more frequent than other pressure techniques [136,143,144,145,146,147,148,149,150].
Furthermore, various researchers successfully welded/brazed HEAs [52,53,54,55,151]. Guo et al. [52] reviewed arc welding, laser welding, electron beam welding, friction stir welding to join HEAs and conducted the microstructural analysis on the welded structures. Filho et al. [54] gave a general review on the properties of welded HEAs parts and Tillmann et al. [151] reviewed HEAs brazing. Lopez et al. [53] reviewed fusion based welding (i.e., for CoCrFeNiMn and other related HEA systems) and solid state welding. Scutelnicu et al. [55] reviewed friction stir, electron and laser beam, tungsten inert gas welding techniques for CoCrFeMnNi, AlCoCrCuFeNi, AlCrFeCoNi and CoCrFeNi alloys.

2.2. Additive Manufacturing of HEAs

3-D printing in manufacturing industries, when properly applied, not only makes a design phase more efficient and economic but also brings thoughtful impacts on product design. Recent advances in additive manufacturing (AM) made it more influential throughout the supply chain which generates revenue as well [152]. The additive manufactured HEAs showed improvement in their mechanical properties in comparison to as-cast HEAs [153,154,155,156,157,158,159,160]. Higher cooling rates in AM processes help suppress diffusional phase transformation and increase the chemical homogeneity of HEAs [161]. Under certain circumstances, AM gives a better control over the material processing and helps tailor application-specific microstructures which become more important for the parts for applications under extreme environments. For example, it was demonstrated that fine and tailorable microstructures in HEAs were obtained using AM techniques [162,163,164,165,166,167,168,169], which implies AM can improve the mechanical performance of at least some HEAs. However, this may not be a trivial task as a good understanding of the AM technique and material behavior during the AM process is required [170].
AM of HEAs has been discussed briefly in a few review papers [51,161,171,172] and books [2,173]. Xiaopeng Li [161] discussed the requirements and challenges of AM of HEAs and bulk metallic glasses. Chen et al. [51] examined the microstructural evolution and mechanical properties of AM-processed CoCrFeNi, AlxCoCrFeNi, CoCrFeMnNi and Ti25Zr50Nb50Ta25. Fabricating HEAs by spark plasma sintering (SPS) and their property analyses were discussed in the book chapter “Spark Plasma Sintering of High Entropy Alloys” of [174]. SPS followed by mechanical alloying has largely been used to develop HEAs, which was reviewed in detail by Vaidya et al. [175]. Therefore, SPS studies are not included here.
In this review, studies on the AM of HEAs are tabulated and the mechanical properties of these HEAs are discussed. Table 1, Table 2 and Table 3 detail the HEAs synthesized by selective laser melting (SLM), electron beam melting (EBM) and direct energy deposition (DED), respectively. The performances of these HEAs are discussed in terms of their composition, their microstructure and their mechanical properties, such as ultimate tensile strength (UTS), % elongation at fracture (ε), yield strength (YS), hardness (H), compressive strength (CS), compressive yield strength (CYS), bending strength (BS), bending elongation (δb) and % compression at fracture (C).
Table 1. The compositions, microstructures and mechanical properties of SLM manufactured HEAs.

Source

Alloy Composition

Microstructure (Grain Size)

Result

UTS (MPa), YS (MPa), BS (MPa), δb (mm), ε (%), H, CS (MPa), C (%)

Chen et al. [176]

CoCrFeMnNi

FCC (53.1 µm)

UTS = 281 ± 18, YS = 12.5 ± 0.5, H = 261 ± 7 HV

Niu et al. [169]

CoCrFeMnNi

FCC (<5 µm)

CS = 2447.7

Li et al. [177]

CoCrFeMnNi + TiNp nanoparticles

FCC

UTS = 601–1036, ε = 12–30

Li et al. [178]

CoCrFeMnNi + Fe based metallic glass

FCC

UTS = 916–1517

Li et al. [179]

CoCrFeMnNi + TiN nanoparticles

FCC

-

Kim et al. [180]

(CoCrFeMnNi)C

FCC (180–330 nm)

YS = 800–900, ε = 25–30

Li et al. [181]

CoCrFeMnNi + 12 wt% nano-TiNp

FCC (<2 µm)

UTS = 1100

Piglione et al. [182]

CoCrFeMnNi

FCC (0.52–0.64 µm)

H = 212 HV

Zhu et al. [153]

CoCrFeMnNi

FCC

-

Xu et al. [183]

CoCrFeMnNi

FCC (1–2 µm)

H = 2.84 ± 0.13 GPa

Park et al. [154]

CoCrFeMnNi +1 at%C

FCC (20–35 µm)

UTS = 829–989, YS = 741, ε = 24.3

Ren et al. [184]

CoCrFeMnNi

-

-

Dovgyy et al. [185]

CoCrFeMnNi

FCC & cubic (0.2–0.8 µm)

-

Zhou et al. [155]

CoCrFeNi + 0.5 at%C

FCC (40–50 µm)

UTS = 776–797, YS = 630–656, ε = 7.7–13.5

Wu et al. [186]

CoCrFeNi + 0.5 at%C

FCC (40–50 µm)

UTS = 795, YS = 638

Lin et al. [98]

CoCrFeNi

FCC

 

Sun et al. [187]

CoCrFeNi

-, ~3 mm in length and ~200 μm in width

UTS = 676.7–691, YS = 556.7–572, ε = 12.4–17.9

Song et al. [188]

CoCrFeNi + N (1.8%)

FCC

UTS = 600–853, YS = 520–650, ε = 27

Zhou et al. [189]

(CoCrFeNi)1−x (WC)x

FCC

H = 603–768 HV

Brif et al. [156]

CoCrFeNi

FCC

UTS = 480–745, YS = 402–600, ε = 8–32, H = 205–238

Niu et al. [190]

AlCoCrFeNi

Disordered (A2) + Ordered (B2) BCC

H = 632.8 HV

Karlsson et al. [170]

AlCoCrFeNi

FCC & BCC (<20 µm)

-

Peyrouzet et al. [157]

Al0.3CoCrFeNi

FCC (width~13 and length~70–120 µm)

UTS = 896, YS = 730, ε = 29

Sun et al. [158]

Al0.5CoCrFeNi

FCC & BCC (1 µm)

UTS = 878, YS = 609, H = 270HV

Zhou et al. [160]

Al0.5CoCrFeNi

FCC

UTS = 721, YS = 579, ε = 22

Luo et al. [191]

AlCrCuFeNi

BCC (avg. width~4 µm)

CS = 1655.2–2052.8, C = 6.5–6.8

Luo et al. [192]

AlCrCuFeNix (2 ≤ x ≤ 3)

FCC (thickness~490 nm) & BCC (~140 nm)

Avg. thickness of both ~ 650 nm

UTS = 957, ε = 14.3

Li et al. [112]

AlCoCuFeNi

BCC

YS = 744, ε = 13.1, CS = 1600

Yao et al. [193]

AlCrFeNiV

FCC (width~15 µm, length~75–200 µm)

UTS = 1057.47, ε = 30.3

Wang et al. [194]

AlCoCrCuFeNi

FCC & BCC

H = 710.4 HV

Wang et al. [195]

AlMgScZrMn

Al3 (Sc, Zr) (1–10 nm + 7 µm)

UTS = 394, ε = 10.5

Sarawat et al. [196]

AlCoFeNiV0.9Sm0.1

AlCoFeNiSm0.1TiV0.9

AlCoFeNiSm0.05TiV0.95Zr,

AlCoFeNiTiVZr

FCC

H~42.8–86.7 HV

Agrawal et al. [197]

Fe40Mn20Co20Cr15Si5

HCP

UTS = 1100, YS = 530, ε = 30

Zhang et al. [198,199]

NbMoTaW

BCC (13.4 μm)

H = 826 HV

Yang et al. [200,201]

Ni6Cr4WFe9Ti

FCC (300–1000 nm) + unknown phase

UTS = 972, YS = 742, ε = 12.2

Chen et al. [202]

CoCrFeNiMn

FCC + Mn2O3 particles

YS = 620, UTS = 730, ε~12

Litwa et al. [203]

CoCrFeNiMn

FCC

H~320 HV

Zhang et al. [204]

CoCrFeNiMn

FCC

YS~729.6

Kim et al. [205]

CoCrFeNiMn

FCC

YS = 752.6

Choi et al. [206]

CoCrFeNiMn

FCC

 

Su et al. [207]

CrCuFeNi2

Al0.5CrCuFeNi2

Al0.75CrCuFeNi2

AlCrCuFeNi2

FCC

FCC

FCC + BCC/B2

FCC + BCC/B2

 

Peng et al. [208]

CoCrFeNi + Ti coated diamond

CoCrFeNi + diamond

FCC + diamond particles

FCC + Cr7C3 + diamond particles

H = 622 HV, BS = 530, δb = 0.64

H = 615 HV, BS = 925, δb = 0.48

Wang et al. [209]

CoCrFeNiMn

FCC

H = 164–370 HV

Sun et al. [210]

Al0.1CrCuFeNi

Al0.5CrCuFeNi

AlCrCuFeNi

FCC

FCC

FCC + BCC/B2 (NiAl)

 

Ishimoto et al. [211]

Ti1.4Nb0.6Ta0.6Zr1.4Mo0.6

BCC

YS = 1690,

Park et al. [212]

(CoCrFeMnNi)99C1

FCC

YS~741, UTS~874

Lin et al. [213]

CoCrFeNi

FCC

YS = 701 ± 14, UTS = 907 ± 25

Kim et al. [214]

CoCrFeNiMn

FCC

-

Jin et al. [215]

CoCrFeNiMn

FCC

YS = 520 ± 10, UTS = 770 ± 10, ε~25

Lin et al. [216]

Al0.2Co1.5CrFeNi1.5Ti0.3

FCC + σ + L12

YS = 1235, UTS = 1550

Peng et al. [217]

CoCrFeNiMn

FCC

-

Vogiatzief et al. [218]

AlCrFe2Ni2

Heat treatment (750–950 °C, 3 h & 6 h)

FCC + BCC

H = 276–483 HV

Liao et al. [219]

Al0.5FeCrNi2.5V0.2

FCC

H = 220–240 HV

Guo et al. [220]

CoCrFeNiMn

FCC

YS = 622, UTS = 763, ε~16

Kim et al. [221]

(CoCrFeNiMn)100−xCx

FCC (15–22 µm)

YS = 653–753, UTS = 766–911

Zhao et al. [222]

CoCrFeNi

FCC

H = 238–525 HV

Gu et al. [223]

CoCr2.5FeNi2TiW0.5

FCC

YS = 449–581, CS = 823–893, ε = 4.4–9.9, H = 436.7–499.2 HV

Table 2. The compositions, microstructures and mechanical properties of EBM manufactured HEAs.

Source

Alloy Composition

Microstructure (Grain Size)

Result

UTS (MPa), YS (MPa), ε (%), H, CS (MPa), C (%)

Peng et al. [224]

CoCrFeNiMn

FCC

YS = 196

Wang et al. [225]

CoCrFeMnNi

FCC (65)

UTS = 497, 205, H = 157.1HV

Kuwabara et al. [226]

AlCoCrFeNi

BCC & FCC

UTS = 1073, YS = 769, ε = 0–1.2

YS = 944–1015, CS = 1447–1668, C = 14.5–26.4

Wang et al. [227]

AlCoCrFeNi

BCC

-

Fujieda et al. [228]

CoCrFeNiTi

FCC + Cubic

UTS = 1178, YS = 773, ε = 25.8

Popov et al. [229]

Al0.5CrMoNbTa0.5

BCC

 
Table 3. The compositions, microstructures and mechanical properties of DED manufactured HEAs.

Scheme

Alloy Composition

Microstructure (Grain Size)

Result

UTS (MPa), YS (MPa), ε (%), H, CS (MPa), C (%)

Guan et al. [230]

CoCrFeMnNi

FCC (13 μm)

YS = 517, ε = 26

Melia et al. [231]

CoCrFeMnNi

FCC (~4 μm)

UTS = 647–651, YS = 232–424

Li et al. [232]

CoCrFeMnNi

FCC

 

Gao et al. [233]

CoCrFeMnNi

FCC (30–150 μm) + BCC

UTS = 620, YS = 448

Xiang et al. [234,235]

CoCrFeNiMn

FCC

UTS = 400–600

Chew et al. [236]

CoCrFeNiMn

FCC (3.68 ± 0.85 μm)

UTS = 660, YS = 518

Qiu et al. [237]

CoCrFeMnNi

FCC

UTS = 891, YS = 564

Li et al. [238]

CoCrFeMnNi + WC (0–10 wt%)

FCC

UTS = 550–845, YS = 300–675, ε = 9

Amar et al. [239]

CoCrFeMnNi + TiC (0–5 wt%)

FCC

UTS = 550–723, YS = 300–385, ε = 32

Guan et al. [240]

CoCrFeMnNi

AlCoCrFeNiTi0.5

FCC (24 µm)

BCC (7 µm) + FCC

YS = 888–1100, H = 197–657 HV

Wang et al. [241]

CoCrFeNiMo0.2

FCC

UTS = 532–928, ε = 37

Zhou et al. [242]

CoCrFeNiNbx (x = 0–0.2)

FCC

UTS = 400–820, YS = 220–750

Gwalani et al. [243]

AlxCoCrFeNi (x = 0.3–0.7)

FCC

 

Nartu et al. [244]

Al0.3CoCrFeNi

FCC

YS = 410–630, ε = 18–28

Mohanty et al. [245]

AlxCoCrFeNi (x = 0.3–0.7)

FCC + BCC

H = 170–380 HV

Vikram et al. [246]

AlCoCrFeNi2.1

FCC & BCC

YS = 309–711, H = 278 ± 11–316 ± 14 HV

Gwalani et al. [247]

AlCrFeMoVx (x = 0–1)

BCC (68–165 μm)

H = 485–581 HV

Guan et al. [248]

AlCoCrFeNiTi0.5

BCC (12 μm)

-

Malatji et al. [249]

AlCrCuFeNi

BCC & FCC

H = 350 HV,

Dada et al. [250,251]

AlCoCrFeNiCu

AlTiCrFeCoNi

 

H = 600 HV, H = 850 HV

Moorehead et al. [252]

NbMoTaW

BCC

-

Kunce et al. [253]

TiZrNbMoV

BCC

-

Dobbelstein et al. [254]

TiZrNbHfTa

BCC

H = 509 HV0.2

Pegues et al. [255]

CoCrFeNiMn

FCC

-

Li et al. [256]

CoCrFeNiMn

FCC

-

Tong et al. [257]

CoCrFeNiMn

Vacuum arc melting

1 impact Laser shock peening

3 impact Laser shock peening

5 impact Laser shock peening

FCC

 

YS = 320.7, UTS = 531.7

YS = 427.4, UTS = 570.7

YS~435, UTS~600

YS = 489.9, UTS = 639.9

Shen et al. [258]

CoCrFeNi (SiC)x

FCC + Cr7C3 (1 µm)

UTS = 2155–2499, YS = 142–713, H = 139–310

Cai et al. [259]

CoCrFeNi

AlCoCrFeNi

BCC (102.27 µm)

BCC (18.75 µm)

YS = 318, UTS = 440, ε = 8.56

YS = 383, UTS = 533, ε = 10.6

Zhang et al. [260]

NbMoTa

NbMoTaTi

NbMoTaNi

NbMoTaTi0.5Ni0.5

BCC

BCC + α-Ti

BCC

BCC + Ni3Ta + β-Ti

YS = 1252, CS = 1282, ε = 15

YS = 1200, CS = 1350, ε = 23

YS = 1350, CS = 1380, ε = 11

YS = 1750, CS = 2277.79, ε = 15

CS of NbMoTaTi0.5Ni0.5 at 600, 800 and 1000 °C is 1699.75 MPa, 1033.63 MPa and 651.36 MPa

Peng et al. [261]

Al0.3CoCrFeNi

FCC + B2

YS = 373–476, CS = 473–508, ε = 0.6–2.96, H = 208–221 HV

Kuzminova et al. [262]

CoCrFeNi

FCC

YS = 456–551, UTS = 637–658, H = 209–259 HV

Malatji et al. [263]

AlCuCrFeNi

Heat treated (800–1100 °C)

FCC + BCC

H = 310–381 HV

Dong et al. [264]

AlCoCrFeNi2.1

FCC + BCC

YS = 388, UTS = 719, ε~27, H = 221–228

Zhou et al. [265]

CoCrFeNb0.2Ni2.1

Solution treatment (2 h,1250 °C)

96 h aged (650 °C)

FCC + HCP (Laves C14) + Nb rich carbide

YS~340, UTS~735

YS~239, UTS~607

YS~896, UTS~1127, ε~17

Zheng et al. [266]

CoCrFeNiMn

FCC

YS = 330, UTS = 630

Cantor alloy (i.e., CoCrFeMnNi) and its variants have been largely investigated. Apart from SPS, SLM is the most widely studied AM technique for HEAs [196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231]. HEAs that were successfully fabricated by SLM include CoCrFeNiMn [153,154,169,176,177,178,179,180,181,182,183,184,185,188,202,203,204,205,206,209,212,214,215,217,220,221], AlCrFeNiV [193], AlCoCrFeNi [170,190], AlCoCrCuFeNi [194], CoCrFeNi [98,155,186,187,189,208,213,222], CoCr2.5FeNi2TiW0.5 [223], Fe40Mn20Co20Cr15Si5 [197], AlxCoCrFeNi [157,158,160] AlCoCuFeNi [112,192], AlxCrCuFeNi [207,210], AlCrCuFeNix [267], AlCrFe2Ni2 [218], Al0.2Co1.5CrFeNi1.5Ti0.3 [216], Ni6Cr4WFe9Ti [200], Ti1.4Nb0.6Ta0.6Zr1.4Mo0.6 [211], Al0.5FeCrNi2.5V0.2 [219] and NbMoTaW [198,199].
Meanwhile, EBM was used to manufacture CoCrFeNiMn [225], AlCoCrFeNi [226,227], CoCrFeNiTi [228] and Al0.5CrMoNbTa0.5 [229]. DED techniques were used to fabricate CoCrFeNiMn [230,231,232,233,234,235,236,237,238,239,240,255,256,257,258,266], CoCrFeNi [258,259,262], Al0.3CoCrFeNi [261], CoCrFeNiMo0.2 [241], CoCrFeNiNbx [242], AlxCoCrFeNi [243,244,245,259,264], AlCoCrFeNi2.1 [246,264], AlCrFeMoVx [247], AlCoCrFeNiTi0.5 [248], AlCrCuFeNi [249,263], AlCoCrFeNiCu/AlTiCrFeCoNi [250,251], NbMoTaW [252], TiZrNbMoV [253], NbMoTaTixNix [260], CoCrFeNb0.2Ni2.1 [265] and TiZrNbHfTa [254].
The microstructures and mechanical behaviors of the HEAs produced by different AM processes are still under investigation by several research groups. The HEAs listed in Table 1, Table 2 and Table 3 mainly have either FCC or BCC microstructures except Co20Cr15Fe40Mn20Si5 which has HCP. Improvement in mechanical properties was reported when HEAs were fabricated with AM [158,169,177,180,188,193,268]. These improvements are mostly attributed to grain refinement. Grain refinement in HEAs is claimed to be due to the high cooling rates as it happens in various other materials [158,200,230]. Moreover, the wear behavior [189,249], thermo-mechanical analysis [199,246], effect of annealing [98], creep behavior [183], residual stresses [232], corrosion behavior [176,198,226,228,231,241,249], strengthening mechanisms [153] and deformation mechanism [237] of additive manufactured HEAs have also been reported.
Particle reinforcement in a HEA matrix with AM has been an area of interest for many researchers lately who expect microstructure refinement and mechanical properties enhancement [123,177,208,212,220,221,269,270,271,272,273,274,275,276,277,278,279,280]. Li et al. [177] introduced nano TiN ceramic particles in a CoCrFeMnNi matrix, which led to equiaxed grains of 5 µm. The same group [179] also fabricated the same composition with SLM followed by laser remelting and obtained ultrafine grains (80% grains less than 2 µm and 90% grains less than 3.5 µm). Song et al. [188] showed that the YS and ductility of CoCrFeNi increased by 25% and 34%, respectively, when doped with 1.8 at% nitrogen. Fu et al. [279] noticed that adding Ti-C-O particles into NbTaTiV increased the UTS, YS and fracture strain up to 2270 MPa, 1760 MPa and 11%, respectively. Amar et al. [239] added TiC into CoCrFeNiMn and found the YS and UTS increased from 300 MPa to 385 MPa and from 550 MPa to 723 MPa, respectively. Similarly, Li et al. [238] embedded WC particles into CoCrFeNiMn alloy and observed improvement in YS from 300 to 675 MPa and UTS from 550 to 845 MPa due to the formation of Cr23C6 precipitates. Li et al. [181] noticed that TiC reinforcement CoCrFeNiMn gave the UTS of around 1100 MPa. Rogal et al. [271] increased the UTS of CoCrFeNiMn up to 1600 MPa by introducing nano-Al2O3 particles. Carbon doping was attempted [154,155,180,186] to enhance the mechanical properties of HEAs. Peng et al. [208] added diamond particles into CoCrFeNi and found out the bending strength was 925MPa. Park et al. [212] added carbon into CoCrFeNiMn ((CoCrFeNiMn)99C1) and noticed that the YS and UTS were ~741 MPa and ~874 MPa, respectively. Similarly, Kim et al. [221] also added carbon into CoCrFeNiMn in a ratio (CoCrFeNiMn)100−xCx (x = 0.5–1.5). The YS for x = 0.5, 1, 1.5 was measured to be 653, 752 and 753 MPa respectively. The UTS for x = 0.5, 1, 1.5 was found to be 766 ± 318.5, 895 ± 22.3 and 911 ± 125.1 MPa, respectively. Shen et al. [258] discussed the effect of SiC particles added to CoCrFeNi. They noticed that adding SiC particles changed the microstructure from the FCC phase to the FCC/Cr2C7 dual phase. The hardness and YS improved significantly from ~139 HV to ~310 HV and ~142 MPa to ~713 MPa, respectively.
Various HEAs have exhibited significant improvement in their mechanical properties after AM synthesis as compared to the as-cast structures of the same compositions [153,154]. Zhou et al. [155] reported that arc-melted CoCrFeNi had the YS of 225 MPa whereas SLM-manufactured CoCrFeNi had the YS of 656 MPa. Brif et al. [156] observed that SLM-manufactured CoCrFeNi showed noticeable improvement in YS from 188 MPa (as-cast) to 600 MPa and in UTS from 457 MPa (as-cast) to 745 MPa. Peyrouzet et al. [157] showed that the YS of Al0.3CoCrFeNi increased from 275 MPa (as-cast) to 730 MPa and the UTS from 502 MPa (as-cast) to 896 MPa when manufactured with SLM. The UTS of as-cast Al0.3CoCrFeNi was 522 MPa and it was increased to 878 MPa with SLM processing [158]. Arc-melted Al0.5CoCrFeNi had the YS of 334 MPa and the UTS of 709 MPa [159]. SLM increased the YS up to 579 MPa and the UTS up to 721 MPa [160].
Moreover, the CS of AlCrCuFeNi was 2052 MPa when fabricated with SLM and 1750 ± 15 MPa [281] with arc-melting. The hardness of AlCoCrCuFeNi improved from 500 to 710 Hv [194] by using SLM. The YS of AlMgScZrMn manufactured with arc melting, SPS, and SLM is 188 ± 2.3 MPa, 231 ± 3 Mpa and 394 Mpa respectively [195]. Agrawal et al. [197] reported that the YS of as-cast and SLM-printed Fe40Mn20Co20Cr15Si5 was 420 ± 20 Mpa and 530 ± 40 Mpa, respectively. The YS of CoCrFeNiMn was 2.5 times higher (around 518 Mpa) [236] with DED in comparison to that of cast parts (209 Mpa) [282] at room temperature (RT). Furthermore, the as-cast AlCoCrFeNi had the UTS of 956 MPa, and the EBM specimen had the UTS of 1073 MPa [226]. Similarly, Fujieda et al. [228] reported that EBM-synthesized CoCrFeNiTi showed the improved tensile strength of around 1178 MPa, which is much stronger than various commercial high corrosion resistant materials such as duplex stainless steel: 655 MPa, super duplex stainless steel: 750–800 MPa and Ni-based super alloys (i.e., Alloy C276: 690 MPa, Alloy 718: 1275 MPa).
Refractory HEA NbMoTaW has shown a drastic reduction in grain size when made with AM. The average grain size of BCC phase was 200 μm in as-cast sample [283] and 13.4 μm in SLM-processed sample. Additionally, this alloy did not follow the rule of mixtures. Instead, it showed the cocktail effect for the hardness of the final structure. The hardness of Nb, Mo, Ta and W was in the range of 85–410 HV but the final hardness of SLM processed NbMoTaW was measured to be 826 HV [198]. Senkov et al. [284] commented that NbMoTaW did not have any abrupt hardness changes at high temperatures, consistently exhibiting better hardness properties than superalloys. Moreover, SLM-processed Ni6Cr4WFe9Ti (UTS = 972 MPa, YS = 742 MPa, ε = 12.2%) had ~93% increase in YS, ~50% increase in UTS, and ~77% increase in tensile ductility as compared to the vacuum arc melted samples (UTS = 649 MPa, YS = 385 MPa, ε = 6.9%) [200,201].
In summary, various studies have successfully manufactured SLM, EBM and DED techniques. They have also shown that the properties of HEAs could be altered by changing the input parameters for AM process. For example, CoCrFeNiMn was manufactured with SLM by multiple researchers [153,154,169,176,177,178,179,180,181,182,183,184,185,188,202,203,204,205,206,209,212,214,215,217,220,221] and many of them acquired different mechanical properties for CoCrFeNiMn by changing input parameters in AM processes (refer Table 1, Table 2 and Table 3).

3. Applications under Extreme Environments

3.1. Nuclear Applications

Nuclear energy is contributing to around 13% of electricity demand worldwide [285] with negligible carbon emission. The safety, reliability and economy of these nuclear power plants depends heavily on the performances of advanced structural materials under high-energy irradiation and elevated temperatures [286,287]. Radioactive waste handling units also require radiation-tolerant materials. Not to mention nuclear applications, radiation-resistant materials are in great demand in medical and aerospace fields as well.
The typical range of operating temperatures of nuclear reactors spans from 350 to 900 °C as listed in Table 4 [288]. At high temperatures, several effects come into play such as thermal expansion, vacancy concentration, diffusion rate, phase transformation, precipitation, recovery, recrystallization, dislocation climb, creep, grain weakening/migration/growth, oxidation and intergranular oxygen dispersion. With conventional alloys, design strategies for nuclear reactor materials were mostly concerned with tuning the microstructures by various heat treatments, precipitation, cold working and solute atoms to get desired properties. HEAs, though, introduce the concept of modifying compositional complexity of the structural materials to make them suitable for nuclear applications.
Table 4. Core outlet temperature of different gen-IV nuclear reactor coolant [288].

Reactor System

Core Outlet Temperature (°C)

Coolant

Super critical water-cooled reactor

350–620

Water

Sodium-cooled fast reactor

~550

Na liquid metal

Lead-cooled reactor

550–800

Pb, Pb-Bi liquid Metals

Molten salt reactor

700–800

Fluoride salts

Gas-cooled fast reactor

~850

Helium gas

Very high temperature reactor

>900

Helium gas

Currently, reduced activation ferritic/martensitic steels (RAFM) (e.g., F82H, EUROFER 97), are the most popular option for irradiation-resistant structural materials. Oxide dispersion strengthened (ODS) RAFM steels (i.e., EUROFER 97 reinforced with 0.3 wt.% Y2O3 particles), C/C, SiC/C, SiC/SiC, refractory metals/alloys (W, Cr), V and Ti-based alloys are also being used [289,290]. HEAs are considered to be potential candidates for nuclear applications [2,291,292,293]. Yeh et al. [294] mentioned that HEAs are potential candidates for structural materials of the 4th generation nuclear reactor. Previously, the irradiation responses and defect behaviors [65,66], intrinsic transport properties [66], irradiation induced structural changes [295] of HEAs were reviewed. Building upon these reviews, this section mainly focuses on ion irradiation resistance of HEAs.
The majority of the previous ion irradiation studies on HEAs are listed in Table 5 where phases, irradiation conditions and important findings are summarized. These HEAs were studied under Ni, Au, Ag, Ar, He, Kr, or Xe ions irradiation. The most popular strategy to design single-phase HEAs of high irradiation resistance used elements having low activation or thermal neutron absorption cross section [296,297,298,299,300].
Table 5. Summary of irradiation studies on HEAs.

Source

Material (Fabrication)

Phase

Irradiation Conditions (Energy, Ion, Fluence, Temperature)

Jawaharram et al. [301]

CoCrFeNiMn

FCC

2.6 MeV, Ag3+, 1.5 × 10−3 & 1.9 × 10−3 dpa−1 s−1, 23–500 °C

Lu et al. [302]

NiCoFeCr, CoCrFeNiMn

FCC

3 MeV, Ni2+, 5 × 1016 ions·cm−2, 500 °C

Barr et al. [303]

CoCrFeNiMn

FCC

3 MeV, Ni2+, 3 × 1015 ions·cm−2, 500 °C

Lu et al. [304]

CoCrFeNi, CoCrFeNiMn

FCC

1.5 MeV, Ni+, 4 × 1014 & 3 × 1015 ions·cm−2 (peak dose~4 dpa), 500 °C

3 MeV, Ni+, 5 × 1016 ions·cm−2 (peak dose~60 dpa), 500 °C

Tong et al. [305]

CoCrFeNiMn

CoCrFeNi

CoCrFeNiPd

FCC

16 MeV, Ni5+, 8 MeV Ni3+, 4 MeV Ni1+&

2 MeV Ni1+, 0.1–1 dpa, 420 °C

Jin et al. [306]

CoCrFeNi, CoCrFeNiMn

FCC

3 MeV, Ni2+, 5 × 1016 ions·cm−2 (peak dose~53 dpa), 500 °C

Chen et al. [307]

CoCrFeMnNi

Al0.3CoCrFeNi

FCC

FCC

1 MeV, Kr ions, 6.3 × 1015 ions·cm−2, 300 °C

Wang et al. [308]

CoCrFeNiCu

FCC

100 keV, He+, 2.5 × 1017, 5 × 1017 & 1 × 1018 ions·cm−2, RT

He et al. [309]

CoCrFeNi,

CoCrFeNiMn,

CoCrFeNiPd

FCC

electrons, 5 × 1018 e·cm−2·s−1, 400 °C

Yang et al. [310]

CoCrFeNiMn,

CoCrFeNiPd

FCC

3MeV, Ni2+, 5 × 1016 ions·cm−2, 420, 500 & 580 °C

Yang et al. [311]

CoCrFeNiMn

FCC

-, He ion, -, RT & 450 °C

Hashimoto et al. [312]

CoCrFeNiMn,

CoCrFeNiAl0.3

FCC

1250 keV, 1.5 dpa, 300–400 °C

Zhang et al. [313]

CoCrFeNiCu

FCC

3 MeV Ni2+, 1014 ions·cm−2, RT

Yang et al. [314]

CoNi, FeNi, CoCrFeNi

-

FCC

3 MeV, Ni2+, 1.5 × 1016 (peak dose~17 dpa) &

5.0 × 1016 (peak dose~53 dpa) ions·cm−2, 500 °C

Abhaya et al. [315]

CrCoFeNi

FCC

1.5 MeV, Ni2+, 1 × 1015 (peak dose~2 dpa) &

5 × 1016 (peak dose~96 dpa) ions·cm−2, RT

Sellami et al. [316]

CoCrFeNi

 

1.5 MeV, Ni2+, 1 × 1013–1 × 1014 ions·cm−2

21 MeV, Ni2+, 2 × 1013 & 1 × 1014 ions·cm−2, RT

Chen et al. [317]

CoCrFeNi

FCC

275 keV, He+, 5.14 × 1020 ions·m−2, 250, 300, 400 °C

Kombaiah et al. [318]

CoCrFeNi,

Al0.12CoCrFeNi

FCC

3 MeV, Ni2+, 1 × 1017 ions·cm−2 (peak dose~100 dpa), 500 °C

Lu et al. [319]

CoCrFeNiPd

FCC

3 MeV, Ni2+, 5 × 1016 ions·cm−2, 580 °C

Tunes et al. [320]

CrFeNiMn

FCC

30 keV, Xe+, 2.6 × 1016 ions·cm−2, 500 °C

Edmondson et al. [321]

CrFeNiMn

BCC

30 keV, Xe+, 9.3×1016 ions·cm−2

6 keV He+, 6.4 × 1016 ions·cm−2, RT

Fan et al. [322]

CoCrFeNi

FCC

3 MeV, Ni ions, 5 × 1016–8 × 1016 ions/cm2, 580 °C

Chen et al. [81]

CoCrFeNiTi0.2

FCC

275 keV, He2+, 5.14 × 1020 ions·m−2, 400 °C

Lyu et al. [323]

CoCrFeNiMo0.2

FCC

27 keV, electrons, -, RT

Xu et al. [324]

(CoCrFeNi)95Ti1Nb1Al3

FCC

2.5 MeV, Fe ions, 1.5 × 1019 ions·m−2, RT-500 °C

Cao et al. [325]

(CoCrFeNi)94Ti2Al4

FCC

4 MeV, Au ions, 10–49 dpa, RT

Tolstolutskaya et al. [326]

Cr0.18Fe0.4Mn0.28Ni0.14

Cr0.18Fe0.28Mn0.27Ni0.28

Cr0.2Fe0.4Mn0.2Ni0.2

FCC

1.4 MeV, Ar ions, 0, 0.3, 1 & 5 dpa, RT

Kumar et al. [327]

Fe0.27Ni0.28Mn0.27Cr0.18

FCC

3 MeV, Ni2+, 4.2 × 1013, 4.2 × 1014 & 4.2 × 1015 ions·cm−2, RT & 500 °C

3 MeV, Ni2+, 2.43 × 1015 & 2.43 × 1016 ions·cm−2, 400–700 °C

Li et al. [328]

Cr0.18Fe0.27Ni0.28Mn0.27

FCC

Neutron, 8.9 × 1014 n·cm−2.s, 60 °C

Voyevodin et al. [329]

Cr0.2Fe0.4Mn0.2Ni0.2+ Y2O3 + ZrO2

FCC

1.4 MeV, Ar ions, 2.2 × 1015 ions·cm−2, RT

Dias et al. [330]

CuxCrFeTiV

(x = 0.21–1.7)

BCC + FCC

300 keV, Ar+, 3 × 1020 at·m−2, RT

Yang et al. [298]

Al0.3CoCrFeNi

FCC

3 MeV, Au ions, 6 × 1015 ion·cm−2 (peak dose ~31 dpa), 250–650 °C

Gromov et al. [331]

AlCoCrFeNi

-

18 keV, electrons, -, RT

Zhang et al. [299]

AlCrMoNbZr,

(AlCrMoNbZr)N

FCC

400 keV, He+, 8 × 1015 & 8 × 1016 ion·cm−2, RT

Yang et al. [82]

Al0.1CoCrFeNi,

Al0.75CoCrFeNi,

Al1.5CoCrFeNi,

FCC

FCC + B2

A2 + B2

3 MeV, Au ions, 1 × 1014–1 × 1016 ions·cm−2, RT

Xia et al. [83]

Al0.1CoCrFeNi,

Al0.75CoCrFeNi,

Al1.5CoCrFeNi

FCC

FCC + B2

B2 + A2

3 MeV, Au ions, 1 × 1014–1 × 1016 ions·cm−2, RT

Yang et al. [332]

Al0.1CoCrFeNi

FCC

3 MeV, Au ions, 6 × 1015 ions·cm−2, 250–650 °C

Zhou et al. [333]

AlxCoCrFeNi (x = 0–2)

FCC + BCC

1 MeV, Kr2+, -, RT

Zhou et al. [334]

AlxCoCrFeNi,

HfNbTaTiZrV

FCC

Amorphous

MeV Kr & 200 KeV, electrons, 2 dpa, RT & 150 °C

Zhou et al. [335]

HfNbTaTiZrV

BCC

1 MeV Kr2+, -, RT-150 °C

Moschetti et al. [336]

HfNbTaTiZr

BCC

5 MeV, He2+, 1.6 × 1012–4.4 × 1017 ions·cm−2s, 50 °C

Sadeghilaridjani et al. [337]

HfTaTiZrV

BCC

4.4 MeV, Ni2+, 1.08 × 1017 ion·cm−2, RT

Li et al. [338]

HfNbTiZr

BCC

1.5 MeV, He ions, 5 × 1015–1 × 1017 ions·m−2, 700 °C

Kareer et al. [339]

TaTiVZr,

TaTiVCr,

TaTiVNb

BCC

BCC

BCC

2 MeV, V+, 2.26 × 1015 ions·cm−2, 500 °C

Wang et al. [340]

ZrTiHfCuBe,

ZrTiHfCuBeNi,

ZrTiHfCuNi

Amorphous

100 keV, He ions, 5.0 × 1017, 1.0 × 1018 & 2.0 × 1018 ions·cm−2, RT

Lu et al. [80]

Ti2ZrHfV0.5Mo0.2

BCC

3 MeV, He+, 5 × 1015, 1 × 1016 & 3 × 1016 ions·cm−2, 600 °C

Atwani et al. [341]

W0.38Ta0.36Cr0.15V0.11

BCC

1 MeV, Kr+2, 0.0006–8 dpa·s−1, 800 °C

Komarov et al. [342]

(TiHfZrVNb)N

-

500 KeV He2+, 5 × 1016–3 × 1017 ions·cm−2, 500 °C

Gandy et al. [343]

SiFeVCrMo

SiFeVCr

sigma

BCC+ sigma

5 MeV, Au2+, 5 × 1015 ions·cm−2, RT

Patel et al. [344]

V2.5Cr1.2WMoCo0.04

BCC

5 MeV, Au+, 5 × 1015 ion·cm−2 (peak dose~42 dpa), RT

Zhang et al. [345]

Mo0.5NbTiVCr0.25, Mo0.5NbTiV0.5Zr0.25

BCC

400 He2+, 1 × 1017–5 × 1017 ions·m−2, 350 °C

Zhang et al. [346]

Mo0.5NbTiVCr0.25, Mo0.5NbTiV0.5Zr0.25

BCC

400 keV, He2+, peak dose~10.5 dpa, 350 °C

Atwani et al. [347]

WtaCrV

BCC

2 keV, He+, 1.65 × 1017 ions·cm−2, 950 °C

3.2. Wear Behavior

The wear properties of HEAs were studied mostly with pin/ball on a disc set up with antagonist materials such as Al2O3, steels (i.e., SKH51, GCr15, 100Cr6), Si3N4, SiC, ZrO2, 1Cr18Ni9Ti, BN, inconel-718 and WC. For lubrication, mostly dry conditions were used but some studies also used H2O2, deionized water and acid rain (pH = 2). Previously, Tsai and Yeh et al. [351], Kasar et al. [352], Senkov et al. [67], Sharma et al. [16], Zhang et al. [37], Li et al. [42], Menghani et al. [353] and Ayyagari et al. [354] discussed the wear behaviors of HEAs. In this review, we will analyze the tribological studies of HEAs in terms of HEAs content variation, particle reinforcement, media and nitriding/carburizing/sulfurizing, temperature effects and oxide formation. Table 6 provides the details of the compositions, microstructures, methods and results (i.e., wear rate or wear resistance, hardness, friction coefficient) of the wear studies performed so far on HEAs.
Table 6. Wear studies of HEAs.

Source

Composition

Microstructure

Method, Medium, Antagonist Material, Temperature, Wear Rate

Joseph et al. [355]

CoCrFeNiMn

FCC

Pin-on-disc, dry, Al2O3, 600–800 °C, RT, 0.5 × 10−4–3.8 × 10−4 mm3·N−1·m−1

Wang et al. [356]

CoCrFeNiMn

FCC

Ball-on-disc, MoS2-oil lubrication, GCr15, RT-140 °C

Xiao et al. [357]

CoCrFeNiMn

FCC

Ball-on-flat, dry, WC-Co, RT, 0.5 × 10−4–5.4 × 10−4 mm3·N−1·m−1

Jones et al. [358]

CoCrFeNiMn

FCC

Rotary tribometer, -, -, ~0.5 × 10−6 mm3·N−1·m−1

Zhu et al. [359]

CoCrFeNiMn

CoCrFeNiMnV

CoCrFeNiMnNb

CoCrFeNiMnNbV

FCC + HCP (Laves) + σ

Ball-on-disc, dry, Si3N4, RT, 1.85 × 10−5–6.39 × 10−5 mm3·N−1·m−1

Deng et al. [360]

CoCrFeNiMox (x = 0–0.3)

FCC

Ball-on-disc, dry, GCr15, RT, 0.33 × 10−3–0.53 × 10−3 mm3·N−1·m−1

Lindner et al. [361]

CoCrFeNiMn

CoCrFeNi

FCC

FCC

Ball-on-disc, dry, Al2O3, RT

Sha et al. [362]

(CoCrFeNiMn)N

FCC + BCC

Ball-on-disc, dry, ruby, RT, 1 × 10−7–1.4 × 10−6 mm3·N−1·m−1

Xiao et al. [363]

CoCrFeNiMnCx (x = 0–1.2)

FCC

Ball-on-disk, dry, Si3N4, RT, 0.47 × 10−5–6.5 × 10−5 mm3·N−1·m−1

Zhu et al. [277]

CoCrFeNiMn + TiN-Al2O3

FCC + TiN

Ball-on-disc, dry, 440C steel, RT

Cheng et al. [364]

CoCrFeNiMn

Al0.5CoCrFeNiMn

AlCoCrFeNiMn

FCC

FCC + BCC

FCC + BCC

Ball-on-disc, dry, Si3N4, RT-800 °C, 0.5 × 10−4–3.8 × 10−4 mm3·N−1·m−1

Joseph et al. [365]

CoCrFeNiMn

Al0.3CoCrFeNi

Al0.6CoCrFeNi

AlCoCrFeNi

FCC

FCC

FCC + BCC

BCC

Pin-on-disc, dry, Al2O3, 25 & 900 °C

Liu et al. [366]

CoCrFeNiMn + Y2O3

FCC + Y2O3 (particles)

Ball-on-disc, dry, GCr15, RT

Wang et al. [367]

(CoCrFeMnNi)85Ti15

FCC + BCC

Ball-on-disc, dry, Si3N4, RT-800 °C, 4 × 10−6–2.23 × 10−5 mm3·N−1·m−1

Zhang et al. [368]

CoCrFeNi + (Ag or BaF2/CaF2)

FCC

Ball-on-disk, dry, Inconel-718, RT, ~4 × 10−5–40 × 10−5 mm3·N−1·m−1

Geng et al. [369]

CoCrFeNi

FCC

Pin-on-disc, vacuum (4 Pa) & air, Inconel 718, RT, 0.6 × 10−4–8 × 10−4 mm3·N−1·m−1

Zhang et al. [370]

CoCrFeNi + (graphite or MoS2)

FCC

Ball-on-disk, dry, Si3N4, RT-800 °C, ~1 × 10−5–23 × 10−5 mm3·N−1·m−1

Zhou et al. [371]

CoCrFeNiMo0.85

Al0.5CoCrFeNi

FCC

FCC

Slurry jet test-rig, HCl+NaCl, -, 40 °C, -

Zhang et al. [372]

CoCrFeNiMo

FCC

Ball-on-disc, dry, -, RT

Huang et al. [373]

FeCoCrNiSix

FCC + BCC

Ball-on-disk, dry, GCr15, RT

Cui et al. [374]

CoCrFeNiMo

Sulfurized at 260 °C for 2 h

FCC + FeS/MoS2 film

Pin-on-disk, dry, GCr15, RT

Li et al. [375]

CoCrFeNiMo0.2

FCC

Ball on disc, dry, GCr15, RT, 3.9 × 10−4–5.4 × 10−4 mm3·N−1·m−1

Ji et al. [376]

CoCrFeNiCu + 2% MoS2

CoCrFeNiCu + 5% MoS2

CoCrFeNiCu + 20% WC

CoCrFeNiCu + 50% WC

CoCrFeNiCu + 80% WC

FCC + MoS2 (particles)

FCC + MoS2 (particles)

FCC + WC (particles)

FCC + WC (particles)

FCC + WC (particles)

Ball-on-disk, dry, Si3N4, RT

Verma et al. [377]

CoCrFeNiCux (x = 0–1)

FCC

Pin-on-disk, dry, -, RT & 600 °C, ~1.3 × 10−5–2.5 × 10−5 mm3·N−1·m−1

Liu et al. [378]

CoCrFeNiBx (x = 0.5–1.5)

FCC + Borides

Roller friction wear tester, dry, W18Cr5V, RT

Jiang et al. [379]

CoCrFeNiNbx (x = 0–1.2)

FCC + HCP (Laves) HCP (Co2Nb)

Ball-on-disc, dry, BN, RT

Yu et al. [380]

CoCrFeNiNbx (x = 0.5–0.8)

FCC + HCP (Laves)

Pin-on-disk, dry, Si3N4, RT-800 °C, ~1.8 × 10−4–9 × 10−4 mm3·N−1·m−1

Liu et al. [381]

Co10Cr10Fe50Mn30 + graphene nanoplatelets (0.2–0.8 wt%)

FCC

Ball-on-plate, dry, GCr15, RT

Wang et al. [382]

Co10Cr10Fe40Mn40 + WC (10 wt%)

FCC+ WC + M23C6

Ball-on-disc, dry, Si3N4, RT

Derimow et al. [383]

(CoCrCuTi)100−xMnx (x = 5–10)

(CoCrCuTi)100−xMnx (x = 10–20)

FCC + BCC

FCC + HCP (Laves)

Ball-on-disc, dry, GCr15, RT

Guo et al. [384]

CoCrFeNiCuSi0.2 (Ti or C)x (x = 0–1.5)

FCC + TiC

Brooks sliding friction & wear tester, dry, RT

Zhang et al. [385]

(CoCrFeNiTi0.5)Cx (x = 3–12 wt%)

BCC + Cr23C6 + TiC

ML-100 friction and wear tester, -, -, RT

Erdoğan et al. [386]

CoCrFeNiTi0.5

CoCrFeNiTi0.5Al0.5

CoCrFeNiTi0.5Al

FCC

BCC

BCC

Ball-on-disc, dry, WC, RT

Liu et al. [387]

CoCrFeNiMo

CoCrFeNiMox (x ≥ 0.3)

CoCrFeNiMox (x ≥ 1)

FCC

FCC + σ

FCC + σ + µ

Pin-on-disk, dry, YG6, RT, 1 × 10−5–8.5 × 10−5 mm3·N−1·m−1

Moazzen et al. [388]

CoCrFexNi (x = 1–1.6)

FCC + BCC

Pin-on-disk, dry, AISI52100 steel, 20–30 °C, -

Yang et al. [389]

CoCrFeNiMoSix (x = 0.5–1.5)

FCC

Pin-on-disk, dry, Si3N4, RT, 0.292 × 10−4–0.892 × 10−4 mm3·N−1·m−1

Li et al. [390]

CoCrFeNi2V0.5Tix (x = 0.5–1.25)

BCC + (Co,Ni)Ti2

Ball-on-disc, dry, Si3N4, RT, 4.4 × 10−5- 37.5 × 10−5 mm3·N−1·m−1

Islak et al. [391]

CrFeNiMoTi

FCC

Ball-on-flat, dry, 100Cr6, RT, 2.7 × 10−3–9.4 × 10−3 mm3·N−1·m−1

Wen et al. [392]

CrCoNiTiV

FCC + BCC + TiO

HT-1000 tribometer, -, WC, RT & 600 °C

Wang et al. [393]

CuNiSiTiZr

BCC

CJS111A wear tester, dry, -, RT

Cheng et al. [394]

(Fe25Co25Ni25 (B0.7Si0.3)25)100−xNbx

(x = 0–4 wt%)

BCC + HCP (Laves) +

FCC

Ball-on-disc, dry, GCr15, RT, ~1.5 × 10−6–3.6 × 10−6 mm3·N−1·m−1

Yadav et al. [395]

(CuCrFeTiZn)1−xPbx

(x = 0.05–0.2)

FCC + BCC + Pb (particles)

Ball-on-disk, dry, -, SAE 52100, RT, 1.17 × 10−5–50 × 10−5 mm3·N−1·m−1

Gou et al. [396]

CoCrFeNi + WC + Mo2C + NbC

FCC

Ball-on-disc, dry, GCr15, 700 °C

Yadav et al. [397]

(CuCrFeTiZn)100−xPbx (x = 0–10)

(CuCrFeTiZn)100−xBix (x = 0–10)

FCC + BCC

BCC

Ball-on-disk, dry, steel, RT

Cui et al. [398]

AlxCoCrFeNiMn (x = 0–0.75)

FCC + BCC

MDW- 02 abrasive wear tester, RT

Gwalani et al. [399]

Al0.5CoCrFeNi

FCC + B2

Pin-on-disc, dry, Si3N4, RT, 1.8 × 10−5–11 × 10−5 mm3·N−1·m−1

Chen et al. [400]

Al0.6CoCrFeNi

FCC + BCC

Ball-on-plate, dry, Si3N4, RT-600 °C, ~0.5 × 10−4–5 × 10−4 mm3·N−1·m−1

Du et al. [401]

Al0.25CoCrFeNi

FCC

Universal wear testing machine, dry, Si3N4

20–600 °C, ~1.5 × 10−4–3.5 × 10−4 mm3·N−1·m−1

Chen et al. [402]

Al0.6CoCrFeNi

FCC + BCC

Ball-on-block, deionized water & acid rain (pH = 2), seawater, GCr15, RT, 1.58 × 10−4–6.52 × 10−4 mm3·N−1·m−1

Ji et al. [403]

Al3CoCrFeNi

 

Jet erosion testing machine, water and 15 wt% SiO2 particles (350–600 mm), RT

Haghdadi et al. [404]

Al0.3CoCrFeNi

AlCoCrFeNi

FCC

BCC

Scratch testing, dry, -, RT

Fang et al. [405]

Al0.3CoCrFeNi

FCC

Pin-on-disc, dry, -, 900 °C

Wu et al. [406]

Al0.1CoCrFeNi

FCC

Ball-on-block, dry and deionized water, Si3N4, RT, ~0.2 × 10−4–1.86 × 10−4 mm3·N−1·m−1

Nair et al. [407]

Al0.1CoCrFeNi

AlCoCrFeNi

Al3CoCrFeNi

FCC

FCC + BCC (B2)

BCC (B2) + A2 + σ

Ball-on-disc, dry, WC, RT

Kumar et al. [408]

Al0.4CoxCrFeNi (x = 0–1)

-

Pin-on-disc, demineralized water & (demineralized water + 3.5 wt% NaCl), EN-31, RT, 0.81 × 10−4–1.86 × 10−4 mm3·N−1·m−1

Mu et al. [409]

AlCoCrFeNi

BCC + FCC

Ball-on disc, dry, Si3N4, RT

Wu et al. [410]

AlCoCrFeNi

AlCoCrFeNiTi0.5

BCC

Pin-on-disc, dry, Si3N4, RT

Zhao et al. [411]

Al0.8CoCrFeNi

FCC + BCC

Ball-on-disk, dry, deionized water + 0.5 wt% NaCl, RT, ~2 × 10−5–7.5 × 10−5 mm3·N−1·m−1

Kumar et al. [412]

Al0.4CoxCrFeNi (x = 0–0.5)

Al0.4CoxCrFeNi (x = 1)

FCC + BCC

FCC

Pin-on-disk, engine oil (SAE Grade:20W-40), EN-31 steel, RT, 2.1 × 10−5–11 × 10−5 mm3·N−1·m−1

Li et al. [413]

Al0.8CoCrFeNiCu0.5Six

(x = 0–0.5)

FCC + BCC1 + BCC2

-, -, CGr15, RT, 0.9 × 10−6–1.19 × 10−6 mm3·N−1·m−1

Li et al. [272]

(AlCoCrFeNi)100-x (NbC)x

(x = 0–30 wt%)

FCC + BCC

Reciprocating tester, dry, N4Si3, RT

Kafexhiu et al. [414]

AlCoCrFeNi2.1

BCC + FCC

Ball-on-plate, dry, 100Cr6 steel, RT, 7 × 10−5–11 × 10−5 mm3·N−1·m−1

Miao et al. [415]

AlCoCrFeNi2.1

FCC (L12) + BCC (B2)

Ball-on-disk, dry, Al2O3/Si3N4/SiC/GCr15, RT-900 °C, ~1 × 10−4–4.2 × 10−4 mm3·N−1·m−1

Ye et al. [416]

AlCoCrFeNi2.1 + TiC (0–15 wt%)

FCC + B2 + TiC

MM-200 wear testing machine, dry, -, RT

Wang et al. [417]

(AlCoCrFeNi)N

BCC + nitrides (AlN,CrN,Fe4N)

Ball-on block, dry, deionized water & acid rain (pH = 2), Si3N4, RT, 2.8 × 10−5–7 × 10−5 mm3·N−1·m−1

Liu et al. [418]

AlCrCuFeNi2

 

Ball-on-block, dry, simulated rainwater & deionized water, Si3N4, RT, 2.163 × 10−3–0.23 × 10−3 mm3·N−1·m−1

Kong et al. [419]

Al1.8CrCuFeNi2

BCC

MMS-2A roller friction wear tester, dry, -, RT

Malatji et al. [263]

AlCrCuFeNi

FCC + BCC

Ball-on-disk, dry, SiC, RT

Wang et al. [420]

Al1.3CoCuFeNi2

FCC + BCC

Ball-on block, dry, deionized water & acid rain (pH = 2), Si3N4, RT, 1 × 10−4–12 × 10−4 mm3·N−1·m−1

Xiao et al. [421]

AlxCoCrFeNiSi (x = 0.5–1.5)

FCC + BCC

Ball-on-flat, distilled water, WC-12Co, RT, 6.7 × 10−6–5.5 × 10−5 mm3·N−1·m−1

Liu et al. [422]

AlCoCrFeNiSix (0–0.5)

BCC

Pin-on-disk, dry, ZrO2, RT, 1.3 × 10−4–5.1 × 10−4 mm3·N−1·m−1

Hsu et al. [423]

Al0.5CoCrFeNiCuBx (x = 0–1)

FCC + boride precipitates

Pin-on-disk, dry, Al2O3, RT

Chen et al. [424]

Al0.5CoCrFeNiCuTix (x = 0–0.2)

Al0.5CoCrFeNiCuTix (x = 0.4–1) Al0.5CoCrFeNiCuTix (x = 1.2–2)

FCC

FCC + BCC

FCC + BCC + Ti2N

Pin-on-disk, dry, Al2O3, RT

Lobel et al. [425]

AlCoCrFeNiTi

BCC

Ball-on-disc, dry, Al2O3, RT

Lobel et al. [426]

AlCoCrFeNiTi

BCC

Ball-on-plate, dry, 100Cr6 Steel, RT

Wu et al. [427]

AlCoCrFeNiTix (x = 0.5–1)

AlCoCrFeNiTix (x = 1.5)

AlCoCrFeNiTix (x = 2)

FCC + BCC

FCC + BCC + Ti2Ni

FCC + BCC + Ti2Ni + ordered BCC

Cavitation erosion tests, Distilled water+ 3.5 wt% NaCl, RT

Erdogan et al. [428]

AlxCoCrFeNiTiy

(x = 0–0.5, y = 0–0.5)

FCC + BCC

Ball-on-disc, dry, WC, RT, 0.25 × 10−4–1.78 × 10−4 mm3·N−1·m−1, 0.25 × 10−4–1.78 × 10−4 mm3·N−1·m−1

Xin et al. [429]

Al0.2Co1.5CrFeNi1.5Ti0.5 + TiC

FCC

Ball-on-disc, dry, Si3N4, RT, 0.3 × 10−5–12.6 × 10−5 mm3·N−1·m−1

Gouvea et al. [430]

Al0.2Co1.5CrFeNi1.5Ti

FCC

Ball-on-plate, dry, AISI 52,100 steel, RT, 1.6 × 10−8–7.5 × 10−5 mm2·N−1

Chuang et al. [431]

AlxCo1.5CrFeNi1.5Tiy

(x = 0–0.2, y = 0.5–1)

FCC

Pin-on-disk, dry, SKH51 steel, RT, ~4 × 10−4–1.8 × 10−4 mm3·N−1·m−1

Liu et al. [432]

AlCoCrFeNiTi0.8

BCC + B2

Ball-on-disc, dry, Si3N4, RT, 1.36 × 10−6–6.96 × 10−6 mm3·N−1·m−1, 0.7 × 10−4–6 × 10−4 mm3·N−1·m−1

Yu et al. [433]

AlCoCrFeNiTi0.5

BCC1 + BCC2

Pin-on-disk, H2O2, SiC & ZrO2, RT

Lobel et al. [434]

AlCoCrFeNiTi0.5

BCC (A2 + B2)

SRV-Tribometer, dry, Al2O3, 22–900 °C

Chen et al. [435]

Al0.6CoCrFeNiTi

BCC

Pin-on-disc, Dry, Al2O3

RT-500 °C

Yu et al. [436]

AlCoCrFeNiTi0.5

AlCoCrFeNiCu

 

Pin-on-disc, dry, Si3N4

Yu et al. [437]

AlCoCrFeNiCu

AlCoCrFeNiTi0.5

FCC + BCC1

BCC1 + BCC2

Pin-on-disk, H2O2, 1Cr18Ni9Ti steel & ZrO2/SiC ceramic, RT

Jin et al. [438]

AlCoFeNiCu

FCC + BCC

Ball-on-disk, dry, WC, 200–800 °C

Zhu et al. [439]

AlCoFeNiCu + TiC (10–30 wt%)

FCC + BCC

Ball-on-disk, dry, Si3N420–600 °C, ~0.1 × 10−5–6.5 × 10−5 mm3·N−1·m−1

Wu et al. [440]

Al0.5CoCrFeNiCu

Al1.0CoCrFeNiCu

Al2.0CoCrFeNiCu

FCC

FCC + BCC

BCC

Pin-on-disk, dry, SKH-51 steel, RT

Yan et al. [441]

AlCoCrFeNiSi + Ti (C, N)

BCC + FCC

Ball-on-disc, dry, GCr15, RT, -

Li et al. [442]

AlCoCrFeNi + Ti (C,N) + TiB2

FCC

Ball-on-disc, dry, WC-6Co, 200–800 °C, 2.69 × 10−5–8.66 × 0−5 mm3·N−1·m−1

Kumar et al. [443]

AlCoCrCuFeNiSi0.3

AlCoCrCuFeNiSi0.6

FCC + BCC

FCC + BCC + σ

Pin-on-disk, dry, -, RT, -

Xin et al. [444]

Al0.2Co1.5CrFeNi1.5Ti0.5

FCC

Pin-on-disk, dry, Si3N4, 25–800 °C, 1.21 × 10−5–6.7 × 10−5 mm3·N−1·m−1

Karakaş et al. [445]

Al0.07Co1.26Cr1.80Fe1.42Mn1.35Ni1.1

FCC

Ball-on-disc, 3.5%NaCl & 5%H2SO4, -, RT, 16.26 × 10−9–77.84 × 10−8 mm3·N−1·m−1

Xin et al. [446]

Al0.2Co1.5CrFeNi1.5Ti (0.5+x) + Cx (x = 0)

FCC

Pin-on-disk, dry, Si3N4, 25–800 °C, 3.12 × 10−6–12.59 × 10−5 mm3·N−1·m−1

Zhao et al. [447]

AlCrCoFeNiCTax (x = 0–1)

BCC

Pin-on-disk, 3.5%NaCl & air, Si3N4, RT, 1.67 × 10−6–2.22 × 10−5 mm3·N−1·m−1

Ghanbariha et al. [448]

AlCoCrFeNi + ZrO2

FCC + BCC

Pin-on-disk, dry, WC, RT, 1.11 × 10−3–2.52 × 10−3 mm3·N−1·m−1

Li et al. [449]

AlxCrFeCoNiCu (x = 0–0.5)

AlxCrFeCoNiCu (x = 0.5–2)

FCC

FCC + BCC

-, dry, GCr15, RT, 6.64 × 10−7–2.26 × 10−4 mm3·N−1·m−1

Cai et al. [450]

AlCrTiV, AlCrTiVSi

BCC

Nanoindenter G200, dry, CGr15 &Al2O3, RT, -

Chandrakar et al. [451]

AlCoCrCuFeNiSix (x = 0–0.9)

BCC

Pin-on-disk, dry, -, RT, -

Erdogan et al. [452]

AlCrFeNiSi

AlCrFeNix (x = Cu,Co)

BCC

BCC + FCC

Ball-on-disc, dry, WC, RT, -

Duan et al. [453]

AlCoCrFeNiCu

-

Pin-on-disc, H2O2, Si3N4, RT

Chen et al. [454]

Al0.5CoCrFeNiCuVx (x = 0–0.2)

Al0.5CoCrFeNiCuVx (x = 0.4–0.8)

Al0.5CoCrFeNiCuVx (x = 1–2)

FCC

FCC + BCC

BCC

Pin-on-disk, dry, Al2O3, RT, 1 × 10−4–2.7 × 10−4 mm3·N−1·m−1

Gu et al. [455]

AlxMo0.5NbFeTiMn2 (x = 1–2)

BCC

Pin-on-disk, dry, Al2O3, RT

Hsu et al. [456]

AlCoCrFexNiMo0.5 (x = 0.6–2)

BCC + σ

Pin-on-disk, dry, SKH51 steel, RT

Liang et al. [457]

AlCrFe2Ni2W0.2Mo0.75

BCC

Ball-on-disc, deionized water, Al2O3, RT, ~5 × 10−6–22 × 10−6 mm3·N−1·m−1

Qui et al. [458]

Al2CoCrFeCuTiNix (x = 0–2)

FCC + BCC

Tribometer, -, -, RT

Kanyane et al. [459]

AlTiSiMoW

BCC + TiSi2 (ordered FCC)

Ball-on-disc, dry, stainless steel, RT

Huang et al. [460]

AlTiSiVCr

BCC+ (Ti,V)5Si3 precipitates

Ball-on-disc, dry, GCr15 steel, RT,

2 × 10−5–2.5 × 10−5 mm3·N−1·m−1

Zhang et al. [461]

AlTiSiVNi

B2 (NiAl) + (Ti,V)5Si3 + TiN

Ball-on-disc, dry, Si3N4, RT & 800 °C

Lin et al. [462]

AlCoCrNiW

AlCoCrNiSi

W + AlNi + Cr15.58Fe7.42C6

BCC

Pin-on-disc, dry, AISI 52100, RT

Yadav et al. [463]

AlCrFeMnV

(AlCrFeMnV)90Bi10

(AlCrFeMnV)90Bi10 + 10 wt% TiB2

(AlCrFeMnV)90Bi10 + 15 wt% TiB2

BCC

BCC + AlV3 + Bi

BCC + AlV3 + Bi + TiB2

BCC + AlV3 + Bi + TiB2

Ball-on-disk, dry, SAE 52,100 steel, RT, 1.02 × 10−5–7.02 × 10−5 mm3·N−1·m−1

Bhardwaj et al. [464]

AlTiZrNbHf

BCC

Pin-on-disk, dry, CGr15, RT, -

Zhao et al. [465]

AlNbTaZrx (x = 0.2–1)

BCC + HCP

Ball-on-disc, dry, Si3N4, RT, 1.85 × 10−4–2.41 × 10−4 mm3·N−1·m−1

Tuten et al. [466]

TiZrHfNbTa

Amorphous

Ball-on-disc, dry, Al2O3, RT

Pole et al. [467]

TiZrHfTaV,

TiZrTaVW

BCC

Ball-on-disk, dry, Si3N4, RT-500 °C, ~1 × 10−4–8 × 10−4 mm3·N−1·m−1

Ye et al. [468]

TiZrHfNb

BCC

Nano-scratch, dry, diamond indenter, RT

Pogrebnjak et al. [469]

(TiZrHfNbV)N

FCC

Ball-on-disc, dry, Al2O3, 20 °C

Gong et al. [470]

TiZrHfBeCu

TiZrHfBeNi

Ti20Zr20Hf20Be20Cu10Ni10

Ti13.8Zr41.2Ni10Be22.5Cu12.5

Amorphous

Nano-scratch, dry, diamond indenter, RT

Zhao et al. [471]

TiZrNiBeCu

Amorphous

Nano-scratch, dry, diamond indenter, RT

Jhong et al. [472]

(TiZrNbCrSi)Cx (x = 36.7–87.8 at.%)

FCC

Ball-on-disc, dry, 100Cr6 steel, RT, 0.2 × 103.3 × 10−6 mm3·N−1·m−1

Mathiou et al. [473]

TiZrNbMoTa

BCC + HCP

Ball-on disc, dry, 100Cr6 steel, Al2O3, RT, 0.154 × 10−1–0.199 × 10−1 mm3·N−1·m−1

Petroglou et al. [474]

MoTaxNbVTi (x = 0.25–1)

BCC

Ball-on-disk, dry, 100Cr6 steel, RT, 0.19 × 10−6–0.38 × 10−6 g·N−1·m−1

Poulia et al. [475]

MoTaNbVW

BCC

Ball-on-disc, dry, 100Cr6 steel & Al2O3, RT

Poulia et al. [476]

MoTaNbVW

BCC

Ball-on-disc, dry, 100Cr6 steel & Al2O3, RT, 1.05 × 10−4–4.89 × 10−4 mm3·N−1·m−1

Poulia et al. [477]

MoTaNbVTi

BCC + hexagonal C14 Laves + cubic C15 laves

Ball-on disc, dry, 100Cr6 steel, Al2O3, RT

Alvi et al. [478]

MoTaWVCu

BCC

Ball-on-disc, dry, E52100 steel & Si3N4, RT-600 °C, 2.3 × 10−2–5 × 10−2 mm3·N−1·m−1

Hua et al. [479]

TixZrNbTaMo (x = 0.5–2)

BCC

HSR-2M tester, dry, Si3N4, RT, 2.22 × 10−7–2.42 × 10−7 mm3·N−1·m−1

Gu et al. [480]

Ni1.5CrFeTi2.0.5Mox (x = 0–0.25)

Ni1.5CrFeTi2.0.5Mox (x = 0.5–0.25)

BCC

BCC + FCC

Ball-on-disc, dry, Al2O3, RT, 7.99 × 107–2.7 × 107 µm3

This entry is adapted from 10.3390/met11121980

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