In-Situ Imaging of Liquid Phase Separation in Molten Alloys Using Cold Neutrons

Derimow, Nicholas; Santodonato, Louis J.; Mills, Rebecca; Abbaschian, R.

doi:10.3390/jimaging4010005

Cited by 8 publications

(14 citation statements)

References 37 publications

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“…Thus, we may expect that Cu will tend to segregate away from the others. This trend has been observed experimentally, and is supported by simulations 10 , 17 , 30 , 31 .…”

Section: Resultssupporting

confidence: 82%

Predictive multiphase evolution in Al-containing high-entropy alloys

et al. 2018

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The ability to predict and understand phases in high-entropy alloys (HEAs) is still being debated, and primarily true predictive capabilities derive from the known thermodynamics of materials. The present work demonstrates that prior work using high-throughput first-principles calculations may be further utilized to provide direct insight into the temperature- and composition-dependent phase evolution in HEAs, particularly Al-containing HEAs with a strengthening multiphase microstructure. Using a simple model with parameters derived from first-principles calculations, we reproduce the major features associated with Al-containing phases, demonstrating a generalizable approach for exploring potential phase evolution where little experimental data exists. Neutron scattering, in situ microscopy, and calorimetry measurements suggest that our high-throughput Monte Carlo technique captures both qualitative and quantitative features for both intermetallic phase formation and microstructure evolution at lower temperatures. This study provides a simple approach to guide HEA development, including ordered multi-phase HEAs, which may prove valuable for structural applications.

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“…Thus, we may expect that Cu will tend to segregate away from the others. This trend has been observed experimentally, and is supported by simulations 10 , 17 , 30 , 31 .…”

Section: Resultssupporting

confidence: 82%

Predictive multiphase evolution in Al-containing high-entropy alloys

et al. 2018

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“…% Ni (0.25 mole fraction) which is indicated by a dotted line in Figure 9. The calculation of the isopleth for this system shows agreement with previous calculations [21] and experiment [23] for the left hand side of the isopleth (CoCrCu), as there is indeed a significant liquid state miscibility gap for the CoCrCu alloy. The calculations also show that there exists a single-phase liquid region above the miscibility gap until approximately 27.5 at.…”

Section: Discussionsupporting

confidence: 87%

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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“…Traditionally, observing LPS in metallic systems was done via post-mortem analysis via metallography and microscopy, as metals are not transparent to light and have a very small transparency for X-rays. Recently, through the use of neutron transmission imaging techniques, the direct observation of liquid phase separation in metals was made possible via neutron radiographs taken during heating and cooling of immiscible CoCrCu alloys [ 72 ]. These experiments show for the first time an in situ observation of macroscopic LPS in metals and can be applied to any metallic system such that the neutron transmission through the each phase can provide enough contrast between them.…”

Section: Solidification Microstructuresmentioning

confidence: 99%

“…The stable liquid phases then agglomerated and separated at the macro-scale. A full sequence of images in the form of a movie can be found in [ 72 ].…”

Section: Solidification Microstructuresmentioning

confidence: 99%

“…Many of the HEAs studied by Munitz et al contained equiatomic CoCrCu, which was experimentally determined to have a large liquid miscibility gap [ 67 ]. It is peculiar that systems such as CoCrCuFeNi will solidify dendritically [ 18 ], while similar alloys of CoCrCu [ 67 , 71 , 72 ] and CoCuFe [ 7 , 8 , 9 , 10 , 11 , 12 , 14 , 15 , 16 , 17 , 73 ] have been shown to have large liquid miscibility gaps. A recent study by Derimow et al investigated the solidification microstructures of equiatomic CoCrCu with added Fe, Mn, Ni, V, FeMn, FeNi, FeV, MnNi, MnV, and NiV to the composition.…”

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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In-Situ Imaging of Liquid Phase Separation in Molten Alloys Using Cold Neutrons

Cited by 8 publications

References 37 publications

Predictive multiphase evolution in Al-containing high-entropy alloys

Predictive multiphase evolution in Al-containing high-entropy alloys

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

Liquid Phase Separation in High-Entropy Alloys—A Review

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