Microstructural Pattern Formation during Far-from-Equilibrium Alloy Solidification

Ji, Kaihua; Dorari, Elaheh; Clarke, Amy J.; Karma, Alain

doi:10.1103/physrevlett.130.026203

Cited by 21 publications

(25 citation statements)

References 52 publications

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“…whereas the local velocity of the isotherms, i.e. the local solidification velocity, is simply [44]. We adapt the formulation of the anisotropic terms for a hexagonal (hcp) Mg alloy, and apply it in two dimensions (2D), within the basal plane, considering local values of temperature gradient G and growth velocity V estimated via the thermal calculations (section 2.2).…”

Section: Post-processingmentioning

confidence: 99%

“…Meanwhile, when using a physically realistic interface width W = W 0 ∼ 1 nm, PF models may be capable of quantitatively capturing solute trapping [72][73][74][75]. In the model used here [44], the spurious trapping effect due to the use of W/W 0 > 1 is compensated via an increased solute diffusivity through the interface. For a given value of S = W/W 0 , the interpolation function for the diffusivity across the interface can be chosen to ensure that results for S > 1 remain quantitatively close to those at S = 1 in terms of partition coefficient k(V) and liquidus slope m(V) across a broad range of interface velocity V, where k varies from its equilibrium value k e at moderate V up to k → 1 at high V. By enabling upscaled yet quantitative simulations with S > 1, the resulting PF simulations allow studying the morphological details of solid-liquid interface pattern evolution at experimentally relevant length and time scales.…”

Section: Post-processingmentioning

confidence: 99%

“…These studies have highlighted the key role of the latent heat diffusion in the selection of the band spacing-rendering it essentially unaffected by the temperature gradient [31,32], while bands are inversely proportional to the temperature gradient if latent heat is neglected [30]. Recent phase-field (PF) simulations have reproduced quantitatively the banding mechanism observed in situ in Al-Cu TEM samples [44] and shown that the onset of banding instability was closely approximated by (5), in spite of the underlying linear stability analysis not incorporating anisotropies of excess free energy and kinetic coefficient essential to the interface pattern selection [45][46][47].…”

Section: Introductionmentioning

confidence: 99%

“…The underlying objective of the present article is to investigate, using state-of-the-art quantitative modeling tools, whether solidification conditions relevant to LPBF of Mg alloy WE43 are indeed expected to result in the oscillatory banding instability linked to a strong equilibrium departure at the solid-liquid interface. To do so, we apply a recently proposed quantitative PF model of rapid solidification [44], using local solidification conditions estimated by a thermal model of laser melting and solidification of a powder bed. We explore microstructural patterns expected in different regions of the melt pool, as well as their complex formation dynamics.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Emergence of rapid solidification microstructure in additive manufacturing of a Magnesium alloy

Tourret,

Tavakoli,

Boccardo

et al. 2024

Modelling Simul. Mater. Sci. Eng.

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Bioresorbable Mg-based alloys with low density, low elastic modulus, and excellent biocompatibility are outstanding candidates for temporary orthopedic implants. Coincidentally, metal additive manufacturing (AM) is disrupting the biomedical sector by providing fast access to patient-customized implants. Due to the high cooling rates associated with fusion-based AM techniques, they are often described as rapid solidification processes. However, conclusive observations or rapid solidification in metal AM — attested by drastic microstructural changes induced by solute trapping, kinetic undercooling, or morphological transitions of the solid-liquid interface — are scarce. Here we study the formation of banded microstructures during laser powder-bed fusion (LPBF) of a biomedical-grade Magnesium-rare earth alloy, combining advanced characterization and state-of-the-art thermal and phase-field modeling. Our experiments unambiguously identify microstructures as the result of an oscillatory banding instability known from other rapid solidification processes. Our simulations confirm that LPBF-relevant solidification conditions strongly promote the development of banded microstructures in a Mg-Nd alloy. Simulations also allow us to peer into the sub-micrometer nanosecond-scale details of the solid-liquid interface evolution giving rise to the distinctive banded patterns. Since rapidly solidified Mg alloys may exhibit significantly different mechanical and corrosion response compared to their cast counterparts, the ability to predict the emergence of rapid solidification microstructures (and to correlate them with local solidification conditions) may open new pathways for the design of bioresorbable orthopedic implants, not only fitted geometrically to each patient, but also optimized with locally-tuned mechanical and corrosion properties.

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Section: Post-processingmentioning

confidence: 99%

Section: Post-processingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Emergence of rapid solidification microstructure in additive manufacturing of a Magnesium alloy

Tourret,

Tavakoli,

Boccardo

et al. 2024

Modelling Simul. Mater. Sci. Eng.

View full text Add to dashboard Cite

show abstract

“…In this low-velocity regime, the solid-liquid interface remains close to equilibrium, which is not always the case for typical SLM conditions. Ongoing work specifically focus on extending this kind of study to include kinetic undercooling and solute trapping using recent PF formulations [19,20].…”

Section: Summary and Perspectivesmentioning

confidence: 99%

Phase-field study of polycrystalline growth and texture selection during melt pool solidification

Tavakoli

Tourret

2023

IOP Conf. Ser.: Mater. Sci. Eng.

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Grain growth competition during solidification determines microstructural features, such as dendritic arm spacings, segregation pattern, and grain texture, which have a key impact on the final mechanical properties. During metal additive manufacturing (AM), these features are highly sensitive to manufacturing conditions, such as laser power and scanning speed. The melt pool (MP) geometry is also expected to have a strong influence on microstructure selection. Here, taking advantage of a computationally efficient multi-GPU implementation of a quantitative phase-field model, we use two-dimensional cross-section simulations of a shrinking MP during metal AM, at the scale of the full MP, in order to explore the resulting mechanisms of grain growth competition and texture selection. We explore MPs of different aspect ratios, different initial (substrate) grain densities, and repeat each simulation several times with different random grain distributions and orientations along the fusion line in order to obtain a statistically relevant picture of grain texture selection mechanisms. Our results show a transition from a weak to a strong ⟨10⟩ texture when the aspect ratio of the melt pool deviates from unity. This is attributed to the shape and directions of thermal gradients during solidification, and seems more pronounced in the case of wide melt pools than in the case of a deeper one. The texture transition was not found to notably depend upon the initial grain density along the fusion line from which the melt pool solidifies epitaxially.

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Freezing Shrinkage Dynamics and Surface Dendritic Growth of Floating Refractory Alloy Droplets in Outer Space

Wang,

Liao,

et al. 2024

Advanced Materials

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The freezing shrinkage and dendritic growth are of great importance for various alloys solidified from high temperature liquids to solids since they dominate microstructure patterns and follow‐up processing. However, the microgravity freezing shrinkage dynamics is scarcely explored on the ground as it is hard to suppress the strong natural convection inside liquid alloys. Here, we conduct a series of in‐orbit solidification experiments aboard China Space Station with a long‐term stable 10−5 g0 microgravity condition. A highest temperature up to 2265 K together with substantial liquid undercoolings far from thermodynamically stable state are attained for both Nb82.7Si17.3 and Zr64V36 refractory alloys. Furthermore, we simulate the freezing shrinkage of a droplet without gravity to reveal the liquid‐solid interface migration, temperature gradient, and flow field. It is found that microgravity solidification process leads to freezing shrinkage cavities and distinctive surface dendritic microstructure patterns. The combined effects of shrinkage dynamics and liquid surface flow in outer space result in the dendrites growing not only along the tangential direction but also along the normal direction to the droplet surface. These space experimental results contribute to a further understanding of solidification behavior of liquid alloys under a weaker convection condition, which is often masked by gravity on the ground.This article is protected by copyright. All rights reserved

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Microstructural Pattern Formation during Far-from-Equilibrium Alloy Solidification

Cited by 21 publications

References 52 publications

Emergence of rapid solidification microstructure in additive manufacturing of a Magnesium alloy

Emergence of rapid solidification microstructure in additive manufacturing of a Magnesium alloy

Phase-field study of polycrystalline growth and texture selection during melt pool solidification

Freezing Shrinkage Dynamics and Surface Dendritic Growth of Floating Refractory Alloy Droplets in Outer Space

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