A fracture-resistant high-entropy alloy for cryogenic applications

Gludovatz, Bernd; Hohenwarter, Anton; Catoor, Dhiraj; Chang, Edmond Chin‐Ping; George, E.P.; Ritchie, Robert O.

doi:10.1126/science.1254581

Cited by 4,198 publications

(1,567 citation statements)

References 48 publications

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“…Micro-twining mechanism at cryogenic temperatures Micro-twins have been experimentally observed in most HEAs during deformation, [2][3][4]8,15 particularly at 77 K, and are regarded as a probable reason for excellent tensile properties at 77 K. Previous studies claimed that the low stacking fault energy (SFE) of HEAs is one of the probable reasons for the micro-twinning. 27,28 However, it is not fully understood why HEAs have a low SFE.…”

Section: Resultsmentioning

confidence: 99%

“…1 Particularly, the equiatomic CoCrFeMnNi HEAs have been reported to possess a wide-range of promising properties such as good hightemperature structural stability 2,3 and an excellent balance between strength and ductility, particularly at cryogenic temperatures, typically 77 K, the liquid nitrogen temperature. 4 Even though most HEAs have equiatomic or near equiatomic compositions, it is believed that the equiatomic composition would not be the optimum composition for a wide range of material properties. [5][6][7][8][9][10] To improve a specific material property, one may have to change the alloy composition from the equiatomic composition.…”

Section: Introductionmentioning

confidence: 99%

“…Sluggish diffusion, [11][12][13] severe lattice distortion 14 and microtwinning [2][3][4]8,15 have been mentioned as probable reasons for the typical HEA properties. However, exact mechanisms for such structural reasons are not clearly known yet.…”

Section: Introductionmentioning

confidence: 99%

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Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

et al. 2018

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Although high-entropy alloys (HEAs) are attracting interest, the physical metallurgical mechanisms related to their properties have mostly not been clarified, and this limits wider industrial applications, in addition to the high alloy costs. We clarify the physical metallurgical reasons for the materials phenomena (sluggish diffusion and micro-twining at cryogenic temperatures) and investigate the effect of individual elements on solid solution hardening for the equiatomic CoCrFeMnNi HEA based on atomistic simulations (Monte Carlo, molecular dynamics and molecular statics). A significant number of stable vacant lattice sites with high migration energy barriers exists and is thought to cause the sluggish diffusion. We predict that the hexagonal close-packed (hcp) structure is more stable than the face-centered cubic (fcc) structure at 0 K, which we propose as the fundamental reason for the micro-twinning at cryogenic temperatures. The alloying effect on the critical resolved shear stress (CRSS) is well predicted by the atomistic simulation, used for a design of non-equiatomic fcc HEAs with improved strength, and is experimentally verified. This study demonstrates the applicability of the proposed atomistic approach combined with a thermodynamic calculation technique to a computational design of advanced HEAs.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

et al. 2018

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“…The high-entropy-alloys have remarkable mechanical properties, 13 and enhanced resistance to radiation damage. 14 The alloys are also unusual because all elements have roughly equal concentrations and the dilute impurity approximation is invalid.…”

Section: Introductionmentioning

confidence: 99%

Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

et al. 2017

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The behavior of matter near a quantum critical point is one of the most exciting and challenging areas of physics research. Emergent phenomena such as high-temperature superconductivity are linked to the proximity to a quantum critical point. Although significant progress has been made in understanding quantum critical behavior in some low dimensional magnetic insulators, the situation in metallic systems is much less clear. Here, we demonstrate that NiCoCr x single crystal alloys are remarkable model systems for investigating quantum critical point physics in a metallic environment. For NiCoCr x alloys with x ≈ 0.8, the critical exponents associated with a ferromagnetic quantum critical point are experimentally determined from low temperature magnetization and heat capacity measurements. All of the five exponents (γ T ≈ 1/2, β T ≈ 1, δ ≈ 3/2, νz m ≈ 2, α T ≈ 0) are in remarkable agreement with predictions of Belitz-Kirkpatrick-Vojta theory in the asymptotic limit of high disorder. Using these critical exponents, excellent scaling of the magnetization data is demonstrated with no adjustable parameters. We also find a divergence of the magnetic Gruneisen parameter, consistent with a ferromagnetic quantum critical point. This work therefore demonstrates that entropy stabilized concentrated solid solutions represent a unique platform to study quantum critical behavior in a highly tunable class of materials.

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“…Recently, this aspect of material research has expanded past that of the conventional alloy (consisting of 1 or 2 principle components) into a new class of highly alloyed materials, high-entropy alloys (HEAs). This field has gained attention [5][6][7] due to findings of higher strengths [8,9], ductility [10] and other interesting properties [11] pertaining to this class. Efforts to design, characterise and utilise HEAs are currently underway globally.…”

Section: Introductionmentioning

confidence: 99%

Predicting the formation and stability of single phase high-entropy alloys

King

Middleburgh

McGregor³

et al. 2016

Acta Materialia

302

120

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Abstract:A method for rapidly predicting the formation and stability of undiscovered single phase high-entropy alloys (SPHEAs) is provided. Our software implementation of the algorithm uses data for 73 metallic elements and rapidly combines them -4, 5 or 6 elements at a time -using the Miedema semi-empirical methodology to yield estimates of formation enthalpy. Approximately 186,000,000 compositions of 4, 5 and 6 element alloys were screened, and ~1,900 new equimolar SPHEAs predicted. Of the 185 experimentally reported HEA systems currently known, the model correctly predicted the stability of the SPHEA structure in 177. The other sixteen were suggested to actually form a partially ordered solid solution -a finding supported by other recent experimental and theoretical work. The stability of each alloy at a specific temperature can also be predicted, allowing precipitation temperatures (and the likely precipitate) to be forecast. This combinatorial algorithm is described in detail, and its software implementation is freely accessible through a webservice allowing rapid advances in the design, development and discovery of new technologically important alloys. , and re-iterated by others since then [1,12], defines a HEA as any alloy consisting of 5 or more elements between 5 -35 at. %. As such, this type of HEA will usually possess a microstructure consisting of two or more distinct phases, some of which are likely to be brittle intermetallic compounds. Although, multiphase strengthening is sometimes desirable in alloys, a large amount of any brittle phase will generally make an alloy unusable as a structural material and such HEAs are therefore mundane. However, as will be discussed shortly, in a few special cases, the additional entropy of the multi-element composition will stabilise a microstructure consisting of either (i) a single solid solution having one of the simple close-packed crystal structures (FCC, HCP or BCC) or (ii) a duplex microstructure consisting of two such simple solid solutions. Generally, it is these non-trivial examples of HEA that interest investigators.This is because the resulting random solid solution(s) will exhibit a combination of ductility coupled with significant solid solution hardening. We recommend use of the term single 2 phase high-entropy alloy (SPHEA) as a more restrictive term to differentiate the rare and desirable single phase type of HEA from generic examples of multiphase HEAs.Combining Yeh's compositional limits [7] with the requirement for a single phase solid solution, we can define a SPHEA as an alloy with  4 alloying elements, at least 4 of which with a molar ratio between 0.33 -1 to that of the highest contributing element. These alloys must be able to display a single phase of simple, random, close-packed structure below the solidus.We return now to the factors that might stabilise a SPHEA. The prevailing hypotheses were (i) that the simple crystal structure or structures are thermodynamically stabilised, relative to possible intermetallic compounds, by the inc...

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A fracture-resistant high-entropy alloy for cryogenic applications

Cited by 4,198 publications

References 48 publications

Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

Predicting the formation and stability of single phase high-entropy alloys

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