Athermal heterogeneous nucleation of solidification

Quested, T. E.; Greer, A.L.

doi:10.1016/j.actamat.2005.02.028

Cited by 115 publications

(66 citation statements)

References 35 publications

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“…We also find that the free energy of a lensshaped nucleus becomes negative when the line tension is negative and large, which will leads to the barrier-less athermal nucleation 8,37 with no thermal activation process.…”

Section: Line Tensionmentioning

confidence: 75%

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Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

Iwamatsu

2015

The Journal of Chemical Physics

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Line-tension-induced scenario of heterogeneous nucleation is studied for a lens-shaped nucleus with a finite contact angle nucleated on a spherical substrate and on the bottom of the wall of a spherical cavity. The effect of line tension on the free energy of a critical nucleus can be separated from the usual volume term. By comparing the free energy of a lens-shaped critical nucleus of a finite contact angle with that of a spherical nucleus, we find that a spherical nucleus may have a lower free energy than a lens-shaped nucleus when the line tension is positive and large, which is similar to the drying transition predicted by Widom [B. Widom, J. Phys. Chem. 99 2803(1995]. Then, the homogeneous nucleation rather than the heterogeneous nucleation will be favorable. Similarly, the free energy of a lens-shaped nucleus becomes negative when the line tension is negative and large. Then, the barrier-less nucleation with no thermal activation called athermal nucleation will be realized.

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Section: Line Tensionmentioning

confidence: 75%

“…5(b), the scaled energy barrier becomes negative. Then, the nucleation becomes deterministic called athermal nucleation because the nucleation does not involve thermal activation to cross the energy barrier 37 .…”

Section: Resultsmentioning

confidence: 99%

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

Iwamatsu

2015

The Journal of Chemical Physics

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“…

Refinement of Al alloys by TiB 2 has been extensively studied in both industry and academia for several decades [1][2][3][4][5][6][7][8][9][10]. The presence of solutes (e.g.

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mentioning

confidence: 99%

The Heterogeneous Nucleation Sequence at the Interface of TiB₂ in Al Alloys

Hage

Ramasse

et al. 2017

Microsc Microanal

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Refinement of Al alloys by TiB 2 has been extensively studied in both industry and academia for several decades [1][2][3][4][5][6][7][8][9][10]. The presence of solutes (e.g. Ti) enhances the TiB 2 grain refinement potency by tailoring the heterogeneous nucleation interface of TiB 2 [10]. To date, there is still a lack of atomic scale experimental investigations of the heterogeneous nucleation interface of TiB 2 under industrial solidification conditions (e.g. conventional die casting). In order to address these open issues, a combination of atomic scale high angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS) in the dedicated aberration corrected scanning transmission electron microscope (STEM) is used for the characterization of the heterogeneous nucleation interface of TiB 2 in Al alloys, with a special focus on the partitioning of non-interacting solute elements (e.g. Ti and Cu) to TiB 2 . Experiments were carried out on two distinct material systems in order to more accurately elucidate the multiple roles of Ti in Al alloys and to determine the dominant mechanism for grain refinement in Al alloys. Firstly, as a reference, the heterogeneous nucleation interface of TiB 2 in a commercial Al-Ti-B grain refiner (i.e. Al-5Ti-1B) was studied. Secondly, the grain refinement of Al-Cu based alloys with varying Ti content (but with identical growth restrictions to the reference case) was investigated. The heterogeneous nucleation interface of TiB 2 in Al-Cu based alloys was also studied. The effect of the solidification path (i.e. a peritectic reaction and a subsequent peritectic transformation) on the observed nucleation phenomena is also discussed. Figure 1 shows a significant partitioning of Ti to the surface of TiB 2 in the commercial grain refiner (Al5Ti-1B). During solidification, the presence of a Ti-rich monolayer is strongly dependent on the solidification path. This is because the Ti-rich monolayer can potentially be consumed by a peritectic reaction. Figure 2 shows that Ti partitioning is present together with a significant Cu-rich monolayer (most likely Al 2 Cu) on the surface of the TiB 2 particle, in an Al-Cu based alloy. The above discussed Ti and Cu rich monolayers were observed over the whole surface of the respective TiB 2 particles. A nucleation sequence on the basal plane of TiB 2 is proposed. Firstly, Al nucleation occurs on an Al 3 Ti monolayer. Secondly, the Al 3 Ti monolayer is preserved from the subsequent peritectic transformation by a surrounding eutectic reaction layer that forms Al 2 Cu on Al. Based on this nucleation sequence, the absence or presence of an Al 3 Ti monolayer on the basal plane of TiB 2 can be interpreted. The present work provides a clearer picture of the heterogeneous nucleation interface between TiB 2 and Al and demonstrates that an Al 3 Ti monolayer must be present if the grain refinement is growth-limited. Only then can growth restriction and concentration undercooling play their full part.

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“…Taking into account the finding that driving force is doubled when new £ nucleation takes place on an existing £ nucleus, energy barrier for the following £ nucleation on ¤/£ interface is reduced to only a quarter of that for initial £ nucleation, which is one eighth of homogeneous £ nucleation. In both cases, i.e., athermal nucleation 44) and conventional nucleation as a thermal activation process with 1/8 of energy barrier, further £ nucleation on an existing £ nuclei is supposed to be significantly promoted following the initial £ nucleation. In other words, concurrent £ phase nucleation could occur like chain-reaction, after initial £ nucleation is successfully realized.…”

mentioning

confidence: 99%

“…The initial nucleation allows further nucleation on the surface of the initial nucleus with much lower energy barrier, one eighth of the homogeneous nucleation. For the following nuclei, even athermal nucleation 44) may be possible at triple junction between two earlier nuclei and matrix. These secondary nuclei do not need the ¤/¤ GB and thus difference in morphology after the two initial cases eventually vanishes, suggesting that it is experimentally difficult to determine whether the GB triggered the initial nucleation takes place in reality or not.…”

mentioning

confidence: 99%

Concurrent γ-Phase Nucleation as a Possible Mechanism of δ-γ Massive-like Phase Transformation in Carbon Steel: Numerical Analysis Based on Effective Interface Energy

et al. 2015

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Effective interface energies of various homo-and hetero-interfaces of iron were calculated with an aid of phase-field modeling, taking into account geometric constraints by competition among grains or interfaces. Calculated effective interface energies for ¤/£, ¤/¤, and £/£ interfaces are 0.56, 0.44 and 0.37 J/m 2 , respectively. Using two simple geometric models for nucleation on or off an interface in the matrix, the optimal shape of a nucleus at a given radius and undercooling, a critical radius and an energy barrier for nucleation for each possible circumstance were numerically calculated. It is found that, although the energy barrier for £-phase nucleation in homogeneous ¤-phase matrix is more than three orders of magnitude greater than that for homogeneous solidification of ¤-phase, the £ nucleation on a ¤/¤ grain boundary in the solidifying matrix suppresses the energy barrier, increasing a nucleation rate. Furthermore, it is found that the £-phase nucleation on an existing £ nucleus halves undercooling needed with smaller critical radius. This suggests that, once £ nucleation is initiated, then following £ nucleation is promoted by doubled driving force, enabling multiple £ nucleation as in chain reaction. These findings are sufficient to explain experimentally observed phenomena during the ¤-£ massive-like phase transformation even if other factors such as solute re-distribution or transformation is neglected.

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Athermal heterogeneous nucleation of solidification

Cited by 115 publications

References 35 publications

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

The Heterogeneous Nucleation Sequence at the Interface of TiB₂ in Al Alloys

Concurrent γ-Phase Nucleation as a Possible Mechanism of δ-γ Massive-like Phase Transformation in Carbon Steel: Numerical Analysis Based on Effective Interface Energy

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Athermal heterogeneous nucleation of solidification

Cited by 115 publications

References 35 publications

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity

The Heterogeneous Nucleation Sequence at the Interface of TiB2 in Al Alloys

Concurrent &gamma;-Phase Nucleation as a Possible Mechanism of &delta;-&gamma; Massive-like Phase Transformation in Carbon Steel: Numerical Analysis Based on Effective Interface Energy

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The Heterogeneous Nucleation Sequence at the Interface of TiB₂ in Al Alloys

Concurrent γ-Phase Nucleation as a Possible Mechanism of δ-γ Massive-like Phase Transformation in Carbon Steel: Numerical Analysis Based on Effective Interface Energy