Microstructures and liquid phase separation in multicomponent CoCrCuFeNi high entropy alloys

Wu, Peng; Liu, N.; Zhou, Pengjie; Peng, Zhen; Du, Wendong; Wang, Xiao Jing; Pan, Ye

doi:10.1179/1743284715y.0000000127

Cited by 48 publications

(23 citation statements)

References 15 publications

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“…An induction melting study by Wu et al involving CoCrCuFeNi demonstrated the first occurrences of LPS in this alloy [ 116 ]. In Wu’s study, several combinations of the CoCrCuFeNi alloy with varied Fe and Ni were studied to investigate the effects on the microstructure and crystallography of the system.…”

Section: High-entropy Alloys Exhibiting Liquid Phase Separationmentioning

confidence: 99%

“…In Wu’s study, several combinations of the CoCrCuFeNi alloy with varied Fe and Ni were studied to investigate the effects on the microstructure and crystallography of the system. When Fe and Ni were varied to create CoCrCuFe

Ni and CoCrCuFeNi

, spherical Cu-rich separations were observed by post-mortem analysis of the solidified samples [ 116 ]. The authors rationalized that the two alloy compositions with positive mixing enthalpies were too great to be overcome by the entropy of the system, which would thereby lower the overall Gibbs energy of the system in the molten state.…”

Section: High-entropy Alloys Exhibiting Liquid Phase Separationmentioning

confidence: 99%

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Liquid Phase Separation in High-Entropy Alloys—A Review

Derimow

Abbaschian

2018

Entropy

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It has been 14 years since the discovery of the high-entropy alloys (HEAs), an idea of alloying which has reinvigorated materials scientists to explore unconventional alloy compositions and multicomponent alloy systems. Many authors have referred to these alloys as multi-principal element alloys (MPEAs) or complex concentrated alloys (CCAs) in order to place less restrictions on what constitutes an HEA. Regardless of classification, the research is rooted in the exploration of structure-properties and processing relations in these multicomponent alloys with the aim to surpass the physical properties of conventional materials. More recent studies show that some of these alloys undergo liquid phase separation, a phenomenon largely dictated by low entropy of mixing and positive mixing enthalpy. Studies posit that positive mixing enthalpy of the binary and ternary components contribute substantially to the formation of liquid miscibility gaps. The objective of this review is to bring forth and summarize the findings of the experiments which detail liquid phase separation (LPS) in HEAs, MPEAs, and CCAs and to draw parallels between HEAs and the conventional alloy systems which undergo liquid-liquid separation. Positive mixing enthalpy if not compensated by the entropy of mixing will lead to liquid phase separation. It appears that Co, Ni, and Ti promote miscibility in HEAs/CCAs/MPEAs while Cr, V, and Nb will raise the miscibility gap temperature and increase LPS. Moreover, addition of appropriate amounts of Ni to CoCrCu eliminates immiscibility, such as in cases of dendritically solidifying CoCrCuNi, CoCrCuFeNi, and CoCrCuMnNi.

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Section: High-entropy Alloys Exhibiting Liquid Phase Separationmentioning

confidence: 99%

Ni and CoCrCuFeNi

Section: High-entropy Alloys Exhibiting Liquid Phase Separationmentioning

confidence: 99%

Liquid Phase Separation in High-Entropy Alloys—A Review

Derimow

Abbaschian

2018

Entropy

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“…The mechanism for such segregation behavior, however, remains unclear, as there are limited accounts of in-situ research in MPCA solidification. For MPCAs in general, a handful of studies 11,16,17 have employed in-situ XRD to observe solid-state phase transformations under pressure and external stress in MPCAs, but studies that discuss the direct solidification behavior of MPCAs, especially the segregation behavior, are largely limited to postmortem analyses 14,15,[18][19][20][21][22][23][24][25] . Some of these ex-situ investigations 15,22,26 on segregation behavior of Cucontaining MPCAs propose the mechanism of liquid-phase separation to be in play, with the evidence of Cu-rich globular clusters present within the solidified microstructures.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Synchrotron Diffraction and Modeling of Non-Equilibrium Solidification of a MnFeCoNiCu Alloy

Schneiderman

Chuang

Kenesei

et al. 2021

Preprint

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The solidification mechanism and segregation behavior of laser-melted Mn35Fe5Co20Ni20Cu20 was firstly investigated via in-situ synchrotron x-ray diffraction at millisecond temporal resolution. The transient composition evolution of the random solid solution during sequential solidification of dendritic and interdendritic regions complicates the analysis of synchrotron diffraction data via any single conventional tool, such as Rietveld refinement. Therefore, a novel approach combining a hard-sphere approximation model, thermodynamic simulation, thermal expansion measurement and microstructural characterization was developed to assist in a fundamental understanding of the evolution of local composition, lattice parameter, and dendrite volume fraction corresponding to the diffraction data. This methodology yields self-consistent results across different methods. Via this approach, four distinct stages were identified, including: (I) FCC dendrite solidification, (II) solidification of FCC interdendritic region, (III) solid-state interdiffusion and (IV) final cooling with marginal diffusion. It was found out that in Stage I, Cu and Mn were rejected into liquid as Mn35Fe5Co20Ni20Cu20 solidified dendritically. During Stage II, the lattice parameter disparity between dendrite and interdendritic region escalated as Cu and Mn continued segregating into the interdendritic region. After complete solidification, during Stage III, the lattice parameter disparity gradually decreases, demonstrating a degree of composition homogenization. The volume fraction of dendrites slightly grew from 58.3–65.5%, based on the evolving composition profile across a dendrite/interdendritic interface in diffusion calculations. Postmortem metallography further confirmed that dendrites have a volume fraction of 64.7% ± 5.3% in the final microstructure.

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“…Liquid phase separation (LPS) in CoCrCuFeNi has also been observed during supercooling [ 14 , 15 , 16 , 17 ], or by varying concentrations of Fe/Ni [ 18 , 19 , 20 ]. LPS resulting from additions of Mo [ 9 ] and Sn [ 17 ] has also been investigated.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Imaging of Molten High-Entropy Alloys Using Cold Neutrons

et al. 2019

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Real-time neutron imaging was utilized to produce a movie-like series of radiographs for in-situ observation of the remixing of liquid state immiscibility that occurs in equiatomic CoCrCu with the addition of Ni. A previous neutron imaging study demonstrated that liquid state immiscibility can be observed in-situ for the equiatomic CoCrCu alloy. In this follow-up study, equiatomic buttons of CoCrCu were placed alongside small Ni buttons inside an alumina crucible in a high-temperature vacuum furnace. The mass of the Ni buttons was specifically selected such that when melted in the same crucible as the CoCrCu buttons, the overall composition would become equiatomic CoCrCuNi. Neutron imaging was simultaneously carried out to capture 10 radiographs in 20 °C steps from 1000 °C to 1500 °C and back down to 1000 °C. This, in turn, produced a movie-like series of radiographs that allow for the observation of the buttons melting, the transition from immiscible to miscible as Ni is alloyed into the CoCrCu system, and solidification. This novel imaging process showed the phase-separated liquids remixing into a single-phase liquid when Ni dissolves into the melt, which makes this technique crucial for understanding the liquid state behavior of these complex alloy systems. As metals are not transparent to X-ray imaging techniques at this scale, neutron imaging of melting and solidification allows for the observation of liquid state phase changes in real time. Thermodynamic calculations of the isopleth for CoCrCuNix were carried out to compare the observed results to the predictions resulting from the current Thermo-Calc TCHEA3 thermodynamic database. The calculations show a very good agreement with the experimental results, as the calculations indicate that the CoCrCuNix alloy solidifies from a single-phase liquid when x ≥ 0.275, which is close to the nominal concentration of the CoCrCuNi alloy (x = 0.25). The neutron imaging shows that the solidification of CoCrCuNi results from a single-phase liquid. This is evident as no changes in the neutron attenuation were observed during the solidification of the CoCrCuNi alloy.

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Microstructures and liquid phase separation in multicomponent CoCrCuFeNi high entropy alloys

Cited by 48 publications

References 15 publications

Liquid Phase Separation in High-Entropy Alloys—A Review

Liquid Phase Separation in High-Entropy Alloys—A Review

In-Situ Synchrotron Diffraction and Modeling of Non-Equilibrium Solidification of a MnFeCoNiCu Alloy

In-Situ Imaging of Molten High-Entropy Alloys Using Cold Neutrons

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