Concurrent substitutional and displacive phase transformations in Al-Mg-Si nanoclusters

Huis, Marijn A. van; Sluiter, Marcel H. F.; Chen, J. H.; Zandbergen, H.W.

doi:10.1103/physrevb.76.174113

Cited by 14 publications

(11 citation statements)

References 29 publications

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“…7 should likely be interpreted as stressing the complete absence of any drive for incorporating Si onto the β''-Mg5Al2Si4 Al sites. This conclusion, already indicated in earlier studies of bulk β'' [9], is in marked contrast to the conventional hypothesis [11,27] that the more accurate β'' composition is Mg5Si6.…”

Section: Energy Variations Around the β''/Al Structural Interfacecontrasting

confidence: 78%

“…An outstanding question in our studies hence is whether the barrier to the eye atom movement is sufficiently reduced for the process to be thermally activated. We note, however, that earlier calculations on bulk β'' [27] indicate a vanishing barrier for even rather Al-rich (Mg2Al5Si4) phase compositions. Arguably, these results support the possibility of the eye atom movement being triggered in the interface evolution considerations of interest in this work.…”

Section: Energy Variations When Passing the β'' Eye Atomcontrasting

confidence: 71%

“…The pre-β'' → β'' structural transition has been discussed theoretically in earlier work [11,27]. In both cases, gradual composition changes throughout the precipitate were assumed.…”

Section: The β''/Al Interfacesmentioning

confidence: 96%

“…2.2.1, the evolution of β'' appears closely coupled to its precursor phase pre-β''. Despite being typically categorized as a GP zone in the literature, pre-β'' has also been viewed [26,27] as adopting a structure with space group C2/m. In this picture, differences to β'' are confined to the eye atom position, phase composition and level of compositional disorder.…”

Section: The β''/Al Interfacesmentioning

confidence: 99%

“…2b) would likewise appear probable, judged from the close structural connection of pre-β'' and fcc Al. Further, the lower β'' growth temperature may represent an obstacle to eye atom movements near the interface, depending on local composition [27]. This may again promote pre-β'' formation at the interface.…”

Section: The β''/Al Interfacesmentioning

confidence: 99%

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Ab initio interface configuration determination for β″ in Al–Mg–Si: Beyond the constraint of a preserved precipitate stoichiometry

Ehlers¹

2014

Computational Materials Science

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The precipitate-host lattice interface configuration stabilities for the β'' phase in the Al-MgSi alloy system have been examined using density functional theory. Usually, the supercell based calculations underlying such studies assume a preserved precipitate stoichiometry. Relaxing this assumption in the present work, we highlight significant results that may easily be overlooked when the stoichiometry constraint is operative. Our main findings are the following: (i) we reject the often proposed Mg5Si6 composition for β''. (ii) We stress the possibility of significant Mg-Al compositional disorder for the more likely β''-Mg5Al2Si4. Finally, (iii) we propose the existence of more than one locally stable interface configuration for the coherent β''/Al interfaces. It is argued that quantifying the solute atom diffusivity near the interface as well as within β'' is fundamental to addressing the importance of points (ii) and (iii).

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Section: Energy Variations Around the β''/Al Structural Interfacecontrasting

confidence: 78%

Section: Energy Variations When Passing the β'' Eye Atomcontrasting

confidence: 71%

“…The pre-β'' → β'' structural transition has been discussed theoretically in earlier work [11,27]. In both cases, gradual composition changes throughout the precipitate were assumed.…”

Section: The β''/Al Interfacesmentioning

confidence: 96%

Section: The β''/Al Interfacesmentioning

confidence: 99%

Section: The β''/Al Interfacesmentioning

confidence: 99%

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Ab initio interface configuration determination for β″ in Al–Mg–Si: Beyond the constraint of a preserved precipitate stoichiometry

Ehlers¹

2014

Computational Materials Science

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Natural Aging in Al‐Mg‐Si Alloys – A Process of Unexpected Complexity

et al. 2010

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The natural aging behavior of pure ternary Al‐Mg‐Si alloys is investigated by measuring hardness, electrical resistivity and positron lifetime, as well as carrying out thermal analysis and atom probe microscopy. It is found that several distinct temporal stages of natural aging can be distinguished in which one of these quantities shows a characteristic behavior and that these times coincide for many of these measurements. The rate of change in the measured data is correlated with proposed solute dynamics during natural aging for both aging that takes place prior to artificial aging (natural pre‐aging) and after artificial underaging (natural secondary aging) heat treatments. Controlling factors for solute dynamics are discussed.

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Phase stabilization principle and precipitate-host lattice influences for Al–Mg–Si–Cu alloy precipitates

et al. 2014

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In this work, we seek to elucidate a common stabilization principle for the metastable and equilibrium phases of the Al-Mg-Si-Cu alloy system, through combined experimental and theoretical studies. We examine the structurally known well-ordered Al-Mg-Si-Cu alloy metastable precipitates along with experimentally observed disordered phases, using high angle annular dark field scanning transmission electron microscopy. A small set of local geometries is found to fully explain all structures.Density functional theory based calculations have been carried out on a larger set of structures, all fully constructed by the same local geometries. The results reveal that experimentally reported and hypothetical Cu-free phases from the set are practically indistinguishable with regard to formation enthalpy and composition. This strongly supports a connection of the geometries with a bulk phase stabilization principle. We relate our findings to the Si network substructure commonly observed in all Mg-Al-2 Si(-Cu) metastable precipitates, showing how this structure can be regarded as a direct consequence of the local geometries. Further, our proposed phase stabilization principle clearly rests on the importance of metal-Si interactions. Close links to the Al-Mg-Si precipitation sequence are proposed.

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Concurrent substitutional and displacive phase transformations in Al-Mg-Si nanoclusters

Cited by 14 publications

References 29 publications

Ab initio interface configuration determination for β″ in Al–Mg–Si: Beyond the constraint of a preserved precipitate stoichiometry

Ab initio interface configuration determination for β″ in Al–Mg–Si: Beyond the constraint of a preserved precipitate stoichiometry

Natural Aging in Al‐Mg‐Si Alloys – A Process of Unexpected Complexity

Phase stabilization principle and precipitate-host lattice influences for Al–Mg–Si–Cu alloy precipitates

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