On the nature of hexagonality within the solidification structure of single crystal alloys: Mechanisms and applications

Strickland, Joel; Nenchev, Bogdan; Perry, S. J.; Tassenberg, Karl; Gill, S.P.A.; Panwisawas, Chinnapat; Dong, Hongbiao; D’Souza, N.; Irwin, Steve

doi:10.1016/j.actamat.2020.09.019

Cited by 23 publications

(32 citation statements)

References 54 publications

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“…Due to this disorder, a more advanced algorithm than our Delaunay triangulation could have led to a more accurate PDAS estimation [110,[113][114][115]. However, we expect that such methods would have only filtered a handful of nearest neighbor outliers, such that the resulting correction would have been minimal once reported within the nearly two orders of magnitude of PDAS variation discussed here (Figs 7-8).…”

Section: Simulationsmentioning

confidence: 89%

“…2b in Ref. [110]) -in contrast to predominantly regular hexagonal arrays in cellular growth due to the axisymmetry of cells [33,111]. While we chose to leave this aspect out of the scope of the current study, it would be interesting, among future directions, to investigate the influence of the spatial order on the resulting spacing stability range, as well as the possible transition from regular to irregular hexagonal arrays with the appearance of side-branches between cellular and dendritic growth regimes.…”

Section: Simulationsmentioning

confidence: 99%

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Multiscale prediction of microstructure length scales in metallic alloy casting

Bellón

Boukellal

Isensee

et al. 2021

Preprint

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Microstructural length scales, such as dendritic spacings in cast metallic alloys, play an essential role in the properties of structural components. Therefore, quantitative prediction of such length scales through simulations is important to design novel alloys and optimize processing conditions through integrated computational materials engineering (ICME). Thus far, quantitative comparisons between experiments and simulations of primary dendrite arms spacings (PDAS) selection in metallic alloys have been mainly limited to directional solidification of thin samples and quantitative phase-field simulations of dilute alloys. In this article, we combine casting experiments and quantitative simulations to present a novel multiscale modeling approach to predict local primary dendritic spacings in metallic alloys solidified in conditions relevant to industrial casting processes. To this end, primary dendritic spacings were measured in instrumented casting experiments in Al-Cu alloys containing 1 wt% and 4 wt% of Cu, and they were compared to spacing stability ranges and average spacings in dendritic arrays simulated using phase-field (PF) and dendritic needle network (DNN) models. It is first shown that PF and DNN lead to similar results for the Al-1 wt%Cu alloy, using a dendrite tip selection constant calculated with PF in the DNN simulations. PF simulations cannot achieve quantitative predictions for the Al-4 wt%Cu alloy because they are too computationally demanding due to the large separation of scale between tip radius and diffusion length, a characteristic feature of nondilute alloys. Nevertheless, the results of DNN simulations for non-dilute Al-Cu alloys are in overall good agreement with our experimental results as well as with those of an extensive literature review. Simulations consistently suggest a widening of the PDAS stability range with a decrease of the temperature gradient as the microstructure goes from cellular-dendrites to well-developed hierarchical dendrites.

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Section: Simulationsmentioning

confidence: 89%

Section: Simulationsmentioning

confidence: 99%

Multiscale prediction of microstructure length scales in metallic alloy casting

Bellón

Boukellal

Isensee

et al. 2021

Preprint

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“…The great advances in computational power in recent years have facilitated the development of a variety of bulk microstructural feature extraction and characterisation digital tools [ 37 , 38 ]. Their main purpose is to bridge the link between materials characterisation and computation to improve the understanding of process-property relationships and to facilitate the development of sophisticated defect modelling approaches, and eventually, Artificial Intelligence.…”

Section: Introductionmentioning

confidence: 99%

GAKTpore: Stereological Characterisation Methods for Porous Foams in Biomedical Applications

et al. 2021

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In tissue engineering, scaffolds are a key component that possess a highly elaborate pore structure. Careful characterisation of such porous structures enables the prediction of a variety of large-scale biological responses. In this work, a rapid, efficient, and accurate methodology for 2D bulk porous structure analysis is proposed. The algorithm, “GAKTpore”, creates a morphology map allowing quantification and visualisation of spatial feature variation. The software achieves 99.6% and 99.1% mean accuracy for pore diameter and shape factor identification, respectively. There are two main algorithm novelties within this work: (1) feature-dependant homogeneity map; (2) a new waviness function providing insights into the convexity/concavity of pores, important for understanding the influence on cell adhesion and proliferation. The algorithm is applied to foam structures, providing a full characterisation of a 10 mm diameter SEM micrograph (14,784 × 14,915 px) with 190,249 pores in ~9 min and has elucidated new insights into collagen scaffold formation by relating microstructural formation to the bulk formation environment. This novel porosity characterisation algorithm demonstrates its versatility, where accuracy, repeatability, and time are paramount. Thus, GAKTpore offers enormous potential to optimise and enhance scaffolds within tissue engineering.

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“…Consequently, any isotherm curvature must result in (001) plane misorientation and a reduction in single crystal mechanical properties. In directional solidification, the axial component of thermal gradient is the strongest at the bottom of a cast 11 , resulting in the flattest isotherm (Fig. 1 a).…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, bulk mosaicity is expected to increase with height from the chill plate. Furthermore, the variation in (001) misorientation perpendicular to the withdrawal direction should be intrinsically related to the shape of the solid/liquid isotherm 11 . Unfortunately, standard microstructural investigation tools, such as optical and electron microscopy, are limited to 2D sample surface analysis 13 , 14 .…”

Section: Introductionmentioning

confidence: 99%

2D single crystal Bragg-dip mapping by time-of-flight energy-resolved neutron imaging on IMAT@ISIS

Strickland

Tassenberg

Sheppard

et al. 2020

Sci Rep

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The cold neutron imaging and diffraction instrument IMAT, at the second target station of the pulsed neutron and muon source ISIS, is used to investigate bulk mosaicity within as-cast single crystal CMSX-4 and CMSX-10 Ni-base superalloys. Within this study, neutron transmission spectrum is recorded by each pixel within the microchannel plate image detector. The movement of the lowest transmission wavelength within a specified Bragg-dip for each pixel is tracked. The resultant Bragg-dip shifting has enabled crystallographic orientation mapping of bulk single crystal specimens with good spatial resolution. The total acquisition time required to collect sufficient statistics for each test is ~ 3 h. In this work, the influence of a change in bulk solidification conditions on the variation in single crystal mosaicity was investigated. Misorientation of the (001) crystallographic plane has been visualised and a new spiral twisting solidification phenomena observed. This proof of concept work establishes time-of-flight energy-resolved neutron imaging as a fundamental characterisation tool for understanding and visualising mosaicity within metallic single crystals and provides the foundation for post-mortem deduction of the shape of the solid/liquid isotherm.

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On the nature of hexagonality within the solidification structure of single crystal alloys: Mechanisms and applications

Cited by 23 publications

References 54 publications

Multiscale prediction of microstructure length scales in metallic alloy casting

Multiscale prediction of microstructure length scales in metallic alloy casting

GAKTpore: Stereological Characterisation Methods for Porous Foams in Biomedical Applications

2D single crystal Bragg-dip mapping by time-of-flight energy-resolved neutron imaging on IMAT@ISIS

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