A second criterion for sigma phase formation in high-entropy alloys

Tsai, Ming–Hung; Chang, Keng-Che; Li, Jianhong; Tsai, Ruei-Chi; Cheng, An-Hung

doi:10.1080/21663831.2015.1121168

Cited by 142 publications

(30 citation statements)

References 28 publications

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“…Many others have since followed this methodology, using the same parameters or others that provide measures of the same key effects. 163,204,252,253,255,258,[263][264][265][266]271 138,272 have used VEC alongside compositional considerations to predict σ formation in HEAs, while others have compared instances of ordered phase formation (including topologically close-packed phases, TCPs) against the average value of the d-orbital energy level 262,273 and Dx. 274 It has been suggested that Dx it is also an indicator of elemental segregation on casting.…”

Section: Phase Prediction and Alloy Selection In Heasmentioning

confidence: 99%

High-entropy alloys: a critical assessment of their founding principles and future prospects

Pickering

Jones

2016

International Materials Reviews

738

299

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High-entropy alloys (HEAs) are a relatively new class of materials that have gained considerable attention from the metallurgical research community over recent years. They are characterised by their unconventional compositions, in that they are not based around a single major component, but rather comprise multiple principal alloying elements. Four core effects have been proposed in HEAs: (1) the entropic stabilisation of solid solutions, (2) the severe distortion of their lattices, (3) sluggish diffusion kinetics and (4) that properties are derived from a cocktail effect. By assessing these claims on the basis of existing experimental evidence in the literature, as well as classical metallurgical understanding, it is concluded that the significance of these effects may not be as great as initially believed. The effect of entropic stabilisation does not appear to be overarching, insufficient evidence exists to establish the strain in the lattices of HEAs, and rapid precipitation observed in some HEAs suggests their diffusion kinetics are not necessarily anomalously slow in comparison to conventional alloys. The meaning and influence of the cocktail effect is also a matter for debate. Nevertheless, it is clear that HEAs represent a stimulating opportunity for the metallurgical research community. The complex nature of their compositions means that the discovery of alloys with unusual and attractive properties is inevitable. It is suggested that future activity regarding these alloys seeks to establish the nature of their physical metallurgy, and develop them for practical applications. Their use as structural materials is one of the most promising and exciting opportunities. To realise this ambition, methods to rapidly predict phase equilibria and select suitable HEA compositions are needed, and this constitutes a significant challenge. However, while this obstacle might be considerable, the rewards associated with its conquest are even more substantial. Similarly, the challenges associated with comprehending the behaviour of alloys with complex compositions are great, but the potential to enhance our fundamental metallurgical understanding is more remarkable. Consequently, HEAs represent one of the most stimulating and promising research fields in materials science at present.

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Section: Phase Prediction and Alloy Selection In Heasmentioning

confidence: 99%

High-entropy alloys: a critical assessment of their founding principles and future prospects

Pickering

Jones

2016

International Materials Reviews

738

299

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“…In CER-HEA2, the reflection lines of the CoCrFeNiV alloy were totally absent; instead, new lines were observed that were assigned to a mixture of two intermetallics: a C14 Laves phase with a hexagonal structure (a = b = 4.7937(4) Å and c = 7.7816(8) Å) and a sigma phase with a tetragonal structure (a = b = 9.3344(9) Å and c = 4.9119(2) Å). It has been shown that HEAs containing Cr and V are prone to sigma phase formation [26,39].…”

Section: Resultsmentioning

confidence: 99%

A new family of cermets: Chemically complex but microstructurally simple

Obra

Avilés

Torres

et al. 2017

International Journal of Refractory Metals and Hard Materials

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Available online xxxxCermets based on Ti(C,N) have interesting properties, such as high wear resistance, high chemical stability and good mechanical strength at high temperature, but to become a viable alternative to cemented carbides, the fracture toughness and damage tolerance must be significantly improved. Complete solid-solution cermets (CSCs) have been proposed to further improve the mechanical properties of these materials. However, to develop this family of cermets with a high level of quality and reliability, using pre-fabricated complex carbonitrides is necessary instead of unalloyed mixtures as the raw ceramic material. A mechanochemical process called mechanically induced self-sustaining reaction (MSR) is suitable to obtain these complex carbonitrides with high stoichiometric control. On the other hand, high entropy alloys (HEAs), which can also be obtained by mechanochemical processes, are a good candidate to replace the current binder phase in cermets because they exhibit high strength and ductility at high temperature and good resistance to both wear and corrosion. In this work, a new family of CSCs based on (Ti,Ta,Nb)C x N 1−x with HEAs belonging to the Fe-Co-Ni-Cr-Mn-V system as the binder phase is developed by mechanochemical processes. With only two constituent phases, these cermets have a simple microstructure but a high compositional complexity because both the ceramic and binder phases are complex solid solutions with at least five components.

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“…[42] during the preparation of CoCrFeMnNi HEA by mechanical alloying. Moreover, the Cr-rich σ-phase has been found very commonly in Cr-containing HEAs in mechanical alloyed condition [43] as well as in heat treated cast alloys [44]. However, the consolidation of such MA CoCrFeMnNi HEA by SPS was reported to promote the formation of a single phase fcc crystal structure [45], suggesting the dissolution of Cr-rich σ-phase during the consolidation process.…”

Section: Analysis Of Powdersmentioning

confidence: 99%

Tungsten Matrix Composite Reinforced with CoCrFeMnNi High-Entropy Alloy: Impact of Processing Routes on Microstructure and Mechanical Properties

Satyanarayana

Sokkalingam

Jena

et al. 2019

Metals

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Tungsten heavy alloy composite was developed by using novel CoCrFeMnNi high-entropy alloy as the binder/reinforcement phase. Elemental tungsten (W) powder and mechanically alloyed CoCrFeMnNi high-entropy alloy were mixed gently in high energy ball mill and consolidated using different sintering process with varying heating rate (in trend of conventional sintering < microwave sintering < spark plasma sintering). Mechanically alloyed CoCrFeMnNi high-entropy alloy have shown a predominant face-centered cubic (fcc) phase with minor Cr-rich σ-phase. Consolidated tungsten heavy high-entropy alloys (WHHEA) composites reveal the presence of Cr–Mn-rich oxide phase in addition to W-grains and high-entropy alloys (HEA) phase. An increase in heating rate restricts the tungsten grain growth with reduces the volume fraction of the Cr–Mn-rich phase. Finally, spark plasma sintering with a higher heating rate and shorter sintering time has revealed higher compressive strength (~2041 MPa) than the other two competitors (microwave sintering: ~1962 MPa and conventional sintering: ~1758 MPa), which may be attributed to finer W-grains and reduced fraction of Cr–Mn rich oxide phase.

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A second criterion for sigma phase formation in high-entropy alloys

Cited by 142 publications

References 28 publications

High-entropy alloys: a critical assessment of their founding principles and future prospects

High-entropy alloys: a critical assessment of their founding principles and future prospects

A new family of cermets: Chemically complex but microstructurally simple

Tungsten Matrix Composite Reinforced with CoCrFeMnNi High-Entropy Alloy: Impact of Processing Routes on Microstructure and Mechanical Properties

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