An understanding of high entropy alloys from phase diagram calculations

Zhang, Fan; Zhang, Chuan; Chen, Shuanglin; Zhu, Jun; Cao, Wei; Kattner, Ursula R.

doi:10.1016/j.calphad.2013.10.006

Cited by 328 publications

(150 citation statements)

References 20 publications

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“…It also appears that some precipitates were extracted from the matrix during etching. It was noted earlier that the CoCrFeNiMn alloy has a single-phase fcc structure above 873 K but with a mixture of fcc and bcc phases below 873 K or, under some conditions, with a σ phase which is an intermetallic compound having a tetragonal crystal structure [27]. An earlier study suggested that Cr-rich precipitates (bcc and σ phases) are stable at 973 K [20].…”

Section: Resultsmentioning

confidence: 99%

Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Shahmir

Liu

et al. 2017

Materials Science and Engineering: A

106

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A CoCrFeNiMn high-entropy alloy was processed by high-pressure torsion to produce a grain size of ~10 nm and then tested in tension at elevated temperatures from 773 to 1073 K using strain rates in the range from 1.0 × 10 -3 to 1.0 × 10 -1 s -1 . The alloy exhibited excellent ductility at these elevated temperatures including superplastic elongations with a maximum elongation of >600% at a testing temperature of 973 K. It is concluded that the formation of precipitates and the sluggish diffusion in the HEA inhibit grain growth and contribute to a reasonable stability of the fine-grained structure at elevated temperatures. The results show the activation energy for flow matches the anticipated value for grain boundary diffusion in nickel but the strain rate sensitivity is low due to the occurrence of some grain growth at these high testing temperatures.

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Section: Resultsmentioning

confidence: 99%

Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Shahmir

Liu

et al. 2017

Materials Science and Engineering: A

106

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“…For example, while configurational entropy of any solid solution would certainly increase as more elements are added to a composition, there is also an increased likelihood that the introduction of an additional alloying element will cause the formation of a stable new intermetallic phase. This concept is hypothesised by Zhang et al [14] and later confirmed by Senkov et al [15]. Nevertheless, the number of possible combinations is exceedingly large and it is considered feasible that many useful SPHEAs exist.…”

Section: Introductionmentioning

confidence: 91%

“…This prediction arises as Cr-Fe forms a strong σ phase intermetallic in their binary phase diagram [14] but complete segregation of these species will lead to a less favourable Gibbs free energy of the solid solution phase. The balance of this interplay results in a Co and Ni rich alloy.…”

Section: Exploring the Co-cr-fe-ni Systemmentioning

confidence: 99%

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

King

Middleburgh

McGregor³

et al. 2016

Acta Materialia

344

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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“…Their selection and investigation have been done more or less by trial and error [10] since phase diagrams for such multi-component systems are not known. So far, partial vertical cross-sections of phase diagrams have been experimentally studied for the systems Cr-Fe-Co-Ni-Al-Cu [11], Cr-Fe-Co-Ni-Al-Mo [12], Cr-Fe-Co-Ni-Al-Nb [13], and Cr-Fe-Co-Ni-Cu-Ti [14] (note that many authors refer to a mixture of several fcc or bcc and cP2-CsCl type phases as fcc or bcc solid solutions) and simulated by the CALPHAD method for Cr-Fe-Co-Ni-Al [10], Cr-Fe-Co-Ni-Mn [15], and Cr-Nb-Ti-V-Zr [15], which are in agreement with experimental observations of [7,16], and [17], respectively. Some new single-phase HEAs such as fcc (CoFeMnNi, CuNiPdPt, CuNiPdPtRh) and hcp (CoOsReRu) have been calculated [18].…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…According to this approach single-phase solid solutions are assumed in systems, which are characterized by complete solubility or at least have a large solid solution range between their binary pairs [93]. Thermodynamic calculations in [7] and [15] support the conclusion that trends observed in the binary systems are also seen in multicomponent alloys. Another approach, based on the Bozzolo-FerranteSmith method for alloys, was discussed in [94].…”

Section: Systems Of Transition Metals Onlymentioning

confidence: 99%

Single-phase high-entropy alloys – an overview

Kozak

Sologubenko

Steurer

2014

Zeitschrift Für Kristallographie - Crystalline Materials

136

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Abstract:The term "high-entropy alloys (HEAs)" first appeared about 10 years ago defining alloys composed of n = 5-13 principal elements with concentrations of approximately 100/n at.% each. Since then many equiatomic (or near equiatomic) single-and multi-phase multicomponent alloys were developed, which are reported for a combination of tunable properties: high hardness, strength and ductility, oxidation and wear resistance, magnetism, etc. In our paper, we focus on probably single-phase HEAs (solid solutions) out of all HEAs studied so far, discuss ways of their prediction, mechanical properties. In contrast to classical multielement/multiphase alloys, only single-phase multielement alloys (solid solutions) represent the basic concept underlying HEAs as mixing-entropy stabilized homogenous materials. The literature overview is complemented by own studies demonstrating that the alloys CrFeCoNi, CrFeCoNiAl 0.3 and PdFeCoNi homogenized at 1300 and 1100°C, respectively, for 1 week are not singlephase HEAs, but a coherent mixture of two solid solutions.

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An understanding of high entropy alloys from phase diagram calculations

Cited by 328 publications

References 20 publications

Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

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

Single-phase high-entropy alloys – an overview

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