Crystal nucleation in metallic alloys using x-ray radiography and machine learning

Liotti, Enzo; Arteta, Carlos; Zisserman, Andrew; Lui, Andrew; Lempitsky, Victor; Grant, Patrick S.

doi:10.1126/sciadv.aar4004

Cited by 85 publications

(54 citation statements)

References 70 publications

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“…[8,9] It has been suggested and widely embraced that, because particulate nucleant surfaces have finite size, the condition for growth of any incipient solid on the nucleant surface is not determined by classical heterogeneous nucleation considerations, [10][11][12][13][14] but rather must overcome an energy barrier arising from the Gibbs-Thomson curvature effect, beyond which ''freegrowth'' of this solid will take place. [15,16] For a small undercooling DT, in the region of 0.2 K, [12] the critical radius of the nucleating particle r Ã is given by [15][16][17][18] :…”

Section: A Inoculation Of Aluminum Alloysmentioning

confidence: 99%

“…[19] Activation of the smaller TiB 2 clusters is subsequently suppressed by the local recalescence from primary a-Al solidification, along with any solute suppression effects near the grain due to rejection of solute into a diffusion zone around the grain. [18,46] These inactive clusters remain suspended in the liquid (Figure 8(a)) and eventually, as solidification proceeds, become impinged by the liquid/a-Al interface of a primary a-Al grain, as it advances after the onset of free growth and latent heat is progressively removed. There could then be three possible outcomes.…”

Section: Impingement Of Tib 2 Particles By the Advancing Liquid/a-al mentioning

confidence: 99%

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The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

Lui

Grant

Stone

et al. 2019

Metall Mater Trans A

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Primary grain refinement using inoculant additions and intermetallic compound (IMC) phase selection are critical aspects in the solidification of commercial aluminum alloys, controlling the final mechanical properties in service. Although there have been studies which suggest there are explicit interactions between the two phenomena, they have yet to be fully elucidated. Here, through study of intermetallic phase particles extracted from an inoculated casting, key features relating to the nucleation of different intermetallic phases via eutectic reactions are recognized and explained. In particular, rake-like IMCs are identified as initiation points for the deleterious b-AlFeSi IMC phase in a model 6xxx series Al alloy. A mechanism is proposed for how TiB 2 inoculant particles, which are commonly used for primary phase refinement, play a role in enhancing the nucleation of intermetallic phases during eutectic reactions at the liquid/a-Al interface in the final stages of solidification. The implication of this mechanism is that, after the event of primary grain refinement, any unused TiB 2 inoculant particles could be contributing to IMC formation thereby affecting the overall type, size, and distribution of intermetallic phases in the solidified alloy.

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Section: A Inoculation Of Aluminum Alloysmentioning

confidence: 99%

Section: Impingement Of Tib 2 Particles By the Advancing Liquid/a-al mentioning

confidence: 99%

The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

Lui

Grant

Stone

et al. 2019

Metall Mater Trans A

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“…The significant role played by the PNLs in influencing heterogeneous nucleation of the crystalline phase has been well explained for systems with potent nucleant substrates, such as liquid Al with Al-Ti-B inoculation [11][12][13][14] . At the atomic scale, the nuclei formed on potent nucleant substrates (contact angle θ < 20°) are predicted to be only several atoms thick 15 , which can be approximated as two-dimensional (2D) layered structures.…”

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confidence: 99%

Atomistics of pre-nucleation layering of liquid metals at the interface with poor nucleants

et al. 2019

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Liquid layering at heterogeneous solid/liquid interfaces is a general phenomenon, which provides structural templates for nucleation of crystalline phases on potent nucleants. However, its efficacy near poor nucleants is incompletely understood. Here we use a combination of X-ray crystal truncation rod analysis and ab initio molecular dynamics to probe the pre-nucleation liquid layering at the sapphire-aluminium solid/liquid interface. At the sapphire side, a~1.6 aluminium-terminated structure develops, and at the liquid side, two prenucleation layers emerge at 950 K. No more pre-nucleation layer forms with decreasing temperature indicating that nucleation of crystalline aluminium through layer-by-layer atomic adsorption of liquid atoms is not favoured. Instead, the appearance of stochastically-formed nuclei near the substrate is supported by our experiments. Nucleation on poor nucleants is dominated by the stochastic nucleation events which are substantially influenced by the prenucleation layers that determine the surface structure in contact with the nuclei.

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“…The emerging synchrotron X-ray imaging methods, which enable spatially and temporally resolved investigation of structural materials under relevant growth conditions, have displayed the capability to offer unprecedented insights into the growth forms of this and other classes of materials under relevant conditions. [88][89][90] Key opportunities reside in integrating this and other relevant real-time imaging tools with advanced ex situ analytical methods (e.g., EELS; see Sec. IV.A) to draw direct comparisons against the unmodified alloys to elucidate conclusively the role of modifier species.…”

Section: Discussionmentioning

confidence: 99%

Chemical modification of degenerate eutectics: A review of recent advances and current issues

Moniri

Shahani

2018

J. Mater. Res.

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Crystal nucleation in metallic alloys using x-ray radiography and machine learning

Abstract: Synchrotron x-ray radiography and machine learning computer vision help explain alloy effects on metallic crystal formation.

Cited by 85 publications

References 70 publications

The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

Atomistics of pre-nucleation layering of liquid metals at the interface with poor nucleants

Chemical modification of degenerate eutectics: A review of recent advances and current issues

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