In situ investigation of the Columnar-to-Equiaxed Transition during directional solidification of Al–20 wt.%Cu alloys on Earth and in microgravity

Ngomesse, F.; Reinhart, Gunther; Soltani, H.; Zimmermann, G.; Browne, David J.; Sillekens, W.H.; Nguyen-Thi, Henri

doi:10.1016/j.actamat.2021.117401

Cited by 24 publications

(15 citation statements)

References 52 publications

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“…During solidification, crystals often undergo morphological transitions associated with thermal or solutal perturbation. In situ studies of these transitions have mainly focused on the instability of a planar solid/liquid interface [33,34,37,38], the cellular-to-dendritic transition [35,[37][38][39] and the columnar-to-equiaxed transition (CET) [40,[120][121][122][123][124].…”

Section: Morphological Transitionmentioning

confidence: 99%

“…Using the same approach, a CET was also observed in situ in Al-Cu alloys [40,[121][122][123]. Ngomesse et al investigated the CET in an Al-20wt%Cu alloy on Earth and in micro-gravity on board the MASER-14 sounding rocket using X-ray radiography [40].…”

Section: Morphological Transitionmentioning

confidence: 99%

“…Ngomesse et al investigated the CET in an Al-20wt%Cu alloy on Earth and in micro-gravity on board the MASER-14 sounding rocket using X-ray radiography [40]. Unlike the earlier work that reported solutal impingement as the predominant mechanism for CET, this research showed that physical (mechanical) impingement also played a role in inducing CET in both gravity and micro-gravity conditions: shrinkage-induced flow "dragged" the newly formed, free floating equiaxed grains towards the columnar region (i.e., the cooler part of the sample) and blocked the growth of the original columnar front [40]. This observation suggested a significant influence of solidification shrinkage flow, even in the relatively thin ∼200 µm radiography sample.…”

Section: Morphological Transitionmentioning

confidence: 99%

“…Unlike the aforementioned works that largely focused on X-ray imaging techniques, the current work instead presents a comprehensive review of knowledge provided by in situ X-ray imaging, for better understanding of solidification theories. Thanks to the high spatial (sub-micron) and temporal (microseconds) resolution offered by third-generation synchrotron sources, significant progress has been made in the understanding, validation and development of theories and models for near-equilibrium solidification, including solute suppressed nucleation (SSN) of both primary solid-solution α-Al [9][10][11][12][13][14] and secondary ordered intermetallics [15,16], dendritic growth of α-Al [17][18][19][20][21][22] and faceted, twin plane re-entrant (TPRE) growth of Fe-rich intermetallics [23][24][25][26], crystal fragmentation [27][28][29][30][31][32], morphological transition [33][34][35][36][37][38][39][40] and defect formation [41][42][43][44][45][46][47]. The focus of solidification research on Al alloys derives from the relatively easy-to-achieve melting temperatures of around 660 °C, and excellent absorption contrast between Al and typical alloying elements such as Cu and Zn.…”

Section: Introductionmentioning

confidence: 99%

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X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects

2022

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Synchrotron and laboratory-based X-ray imaging techniques have been increasingly used for in situ investigations of alloy solidification and other metal processes. Several reviews have been published in recent years that have focused on the development of in situ X-ray imaging techniques for metal solidification studies. Instead, this work provides a comprehensive review of knowledge provided by in situ X-ray imaging for improved understanding of solidification theories and emerging metal processing technologies. We first review insights related to crystal nucleation and growth mechanisms gained by in situ X-ray imaging, including solute suppressed nucleation theory of α-Al and intermetallic compound crystals, dendritic growth of α-Al and the twin plane re-entrant growth mechanism of faceted Fe-rich intermetallics. Second, we discuss the contribution of in situ X-ray studies in understanding microstructural instability, including dendrite fragmentation induced by solute-driven, dendrite root re-melting, instability of a planar solid/liquid interface, the cellular-to-dendritic transition and the columnar-to-equiaxed transition. Third, we review investigations of defect formation mechanisms during near-equilibrium solidification, including porosity and hot tear formation, and the associated liquid metal flow. Then, we discuss how X-ray imaging is being applied to the understanding and development of emerging metal processes that operate further from equilibrium, such as additive manufacturing. Finally, the outlook for future research opportunities and challenges is presented.

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Section: Morphological Transitionmentioning

confidence: 99%

Section: Morphological Transitionmentioning

confidence: 99%

Section: Morphological Transitionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects

2022

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“…Solidification experiments under microgravity conditions provide unique benchmark data in diffusive conditions [13][14][15]. Indeed, microgravity conditions suppress gravitydriven phenomena, such as sedimentation and convective flow, due to density differences in the liquid [16].…”

Section: Introductionmentioning

confidence: 99%

Influence of Solidification Parameters on the Amount of Eutectic and Secondary Arm Spacing of Al–7wt% Si Alloy Solidified under Microgravity

Roósz

Rónaföldi

et al. 2022

Crystals

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During the solidification of hypoeutectic Al–7% Si alloy, density differences develop in the melt due to variations in concentration and temperature. On Earth, melt flow can occur due to gravity, which then affects the solidification process. The microgravity environment strongly eliminates convection in the melt and allows investigation of the solidification process in purely diffusive circumstances. In this study, four solidification experiments were performed on grain-refined and non-grain-refined Al–7 wt% Si alloy on-board the International Space Station (ISS) in the Materials Science Lab (MSL) to study the effect of solidification parameters (solid/liquid front velocity (v) and temperature gradient (G)) on the grain structure and dendritic microstructure. The grain structure has been analyzed in detail in some earlier studies. The aim of this work was to carry out detailed analysis of the macrosegregation caused by the diffusion of Si from the initial mushy zone during the homogenization step and the subsequent solidification phase of the experiments as well as the correlated distribution of eutectic along the solidification direction. The secondary dendrite arm spacing (SDAS) for different process conditions was also studied. For these two issues, microgravity experimental results were compared to simulation results. The macrosegregation was calculated by the finite difference method. Because the steady-state solidification conditions were never reached, the solidification process was characterized by the average front velocity and temperature gradient. Considering the actual liquidus temperature (TL) caused by macrosegregation, the SDAS was calculated as a function of the average processing parameters and the actual liquidus temperature with the classical Kirkwood’s equation. As a result, good agreement was obtained between the calculated and measured SDAS.

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Benchmark Al-Cu Solidification Experiments in Microgravity and on Earth

Williams

Beckermann

2022

Metall Mater Trans A

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Predicting macrosegregation and grain structure, including the columnar to equiaxed transition (CET), in alloy solidification is an ongoing challenge. Gravity-driven melt convection and transport of unattached solid grains complicate such efforts. Cylindrical samples of aluminum alloys containing 4, 10, and 18 wt pct copper are solidified from the bottom upwards on Earth and in microgravity conditions aboard the International Space Station. The chosen alloys possess primary solid densities that are greater than, equal to, and less than their melt densities promoting different gravity-driven solid transport phenomena. Significant differences in grain structure are observed between microgravity and terrestrial samples. All microgravity samples are entirely equiaxed, while the terrestrial samples exhibit a CET. The columnar grains near the cooled surface in the terrestrial samples can only be attributed to melt convection. The Al-4 wt pct Cu terrestrial sample shows evidence of grain sedimentation, while the Al-18 wt pct Cu terrestrial sample exhibits the effects of grain floatation. Measurements of eutectic fraction and solute concentration in the samples show inverse segregation due to shrinkage-driven flow in all samples. Terrestrially solidified samples have areas of high solute concentration that are not uniformly distributed over the diameter, indicating the presence of melt convection. The eutectic and macrosegregation measurements generally have good correspondence. Temperature, grain structure, eutectic fraction, and macrosegregation data are presented as benchmark data to validate future modeling efforts. Heat flux boundary conditions on the sample are determined using thermal modeling. Thermal process parameters are calculated for all samples.

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In situ investigation of the Columnar-to-Equiaxed Transition during directional solidification of Al–20 wt.%Cu alloys on Earth and in microgravity

Cited by 24 publications

References 52 publications

X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects

X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects

Influence of Solidification Parameters on the Amount of Eutectic and Secondary Arm Spacing of Al–7wt% Si Alloy Solidified under Microgravity

Benchmark Al-Cu Solidification Experiments in Microgravity and on Earth

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