Morphology and Growth Kinetic Advantage of Quenched Twinned Dendrites in Al-Zn Alloys

Salgado-Ordorica, M.A.; Phillion, A.B.; Rappaz, M.

doi:10.1007/s11661-012-1539-0

Cited by 19 publications

(20 citation statements)

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“…Nevertheless, these findings strongly support the doublon conjecture first made by Henry [8] for the morphology of a twinned dendrite tip. Experimental evidence supporting the doublon conjecture is presented in the following companion paper [10].…”

Section: Resultsmentioning

confidence: 91%

“…The small arrow in (c) indicates the solute pile-up that would create the narrow liquid channel in the center of the twinned dendrite trunk. The lateral twin propagation mechanism is encircled at the right tertiary arm of the doublon morphology in (c) [10].…”

Section: The Phase Field Modelmentioning

confidence: 99%

“…Observations of DS specimens with [9] and without quenching [10] indicate that the complex branched morphology of the h1 1 0i and h1 0 0i arms, their better orientation with respect to the liquidus isotherm and the solutal interactions between them and the side arms of regular dendrites are some of the factors that influence their favorable growth kinetics. Moreover, evidence from previous works [6,8,10] suggests that the tip undercooling of such dendrites might be smaller than that of regular dendrites of the same alloy, due to their shape and the solute rejection associated with it. Beyond these experimental facts, there is another important factor that influences the growth of this particular structures.…”

Section: Introductionmentioning

confidence: 99%

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Study of the twinned dendrite tip shape I: Phase-field modeling

2011

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The growth kinetics advantage of twinned aluminum dendrites over regular ones is still an unsolved problem of solidification. Although it is linked to the tip geometry, the influence of a coherent (1 1 1) twin plane on a h1 1 0i twinned dendrite tip is unclear, despite several past experimental observations. In the present contribution, a three-dimensional phase field model implemented on a cluster of parallel computers has been used to simulate the growth of a twinned dendrite under various directional solidification conditions. Only half a dendrite was modeled by replacing the coherent twin plane by a boundary with an appropriate condition on the phase parameter that is equivalent to the Young-Laplace equilibrium condition along the triple line between twinned solid, untwinned solid and liquid. It is found that the small liquid cusp present at the tip rapidly evolves into a doublon-type morphology, i.e. a h1 1 0i dendrite split in its center by a deep and thin liquid pool with the triple line at the root. At high growth rates, the two sides of the doublon tend to coalescence and form small isolated liquid droplets. The positive concentration gradient near the doublon root appears to be rapidly smeared out by back-diffusion in the solid, thus making difficult its quantification through experimental methods. These simulation results are correlated with new experimental evidence presented in a companion paper.

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Section: Resultsmentioning

confidence: 91%

Section: The Phase Field Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of the twinned dendrite tip shape I: Phase-field modeling

2011

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“…the undercooling of the twinned dendrite tip is smaller than that of regular columnar dendrites [22]. Formation of such a long twinned dendrite ( Fig.…”

Section: A Large Twin Dendrite In An Al-zn-cr Specimen Solidified Undmentioning

confidence: 92%

Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al–Zn–Cr alloys: Can icosahedral solid clusters play a role?

2013

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The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or neartwin, relationship with their nearest neighbors when minute amounts of Cr (1000 ppm) are added to the melt. Several occurrences of neighboring grains sharing a nearly common h1 1 0i direction with a fivefold symmetry multi-twinning relationship have been found. These findings are a very strong indication that the primary face-centered cubic Al phase forms on either icosahedron quasicrystals or nuclei of the parent stable Al 45 Cr 7 phase, which exhibits several fivefold symmetry building blocks in its large monoclinic unit cell. They are further supported by thermodynamic calculations and by grains sometimes exhibiting orientations compatible with the socalled interlocked icosahedron. These results are important, not only because they provide an explanation of the nucleation of twinned dendrites in Al alloys, a topic that has remained unclear over the past 60 years despite several recent investigations, but also because they identify a so far neglected nucleation mechanism in aluminum alloys, which could also apply to other metallic systems.

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“…However, the detailed mechanism of the preponderant twinned growth is not entirely clear. While the easy extension of twinned dendrites along their twin planes can be attributed to regular dendrite branching [15,16], there is still some uncertainty about their lateral propagation mechanism, perpendicular to the twin planes.…”

Section: Introductionmentioning

confidence: 99%