Mechanical deformation of dendrites by fluid flow during the solidification of undercooled melts

Dragnevski, Kalin I.; Walker, Daniel J.; Mullis, Andrew M.

doi:10.1016/s1359-6454(02)00186-6

Cited by 69 publications

(43 citation statements)

References 16 publications

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“…Again this would seem to indicate a material that is resistant to nucleation. We have previously observed evidence [28,29] of flow induced deformation in materials processed via the flux encasement technique when electromagnetic heating is used to melt the sample, as it is here. However, the highly regular structure observed in the eutectic would suggest that this is not the case here, which may be related to the apparent high viscosity of the melt.…”

Section: Resultssupporting

confidence: 64%

The formation of regular αNi-γ(Ni31Si12) eutectic structures from undercooled Ni–25 at.% Si melts

Ahmad

Mullis

2012

Intermetallics

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Undercooling experiments have been performed on an Ni-25.2 at.% Si alloy using a flux encasement technique, with a maximum undercooling of 160 K having been achieved. Double recalescence was observed at all undercoolings, with crystal growth velocities being measured for the first recalescence event. These velocities were extremely low, with a maximum value of 0.018 m s -1 being recorded. At all undercoolings a eutectic structure was observed, comprising alternating lamellae of single phase γ(Ni 31 Si 12 ) and Ni-rich lamellae containing of a fine (200-400 nm) dispersion of βNi 3 Si and αNi. This is contrary to the equilibrium phase diagram from which direct solidification to βNi 3 Si would be expected for undercoolings in excess of 53 K. We postulate that the direct solidification of βNi 3 Si from the melt is suppressed, with an α-γ eutectic being formed instead. The α appears to be supersaturated in Si and undergoes a eutectoid decomposition to α and βNi 3 Si, giving rise to the observed second recalescence.

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Section: Resultssupporting

confidence: 64%

The formation of regular αNi-γ(Ni31Si12) eutectic structures from undercooled Ni–25 at.% Si melts

Ahmad

Mullis

2012

Intermetallics

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“…Low-angle boundaries have also been reported in other systems such as single-crystal solidification of Mo-Re alloys [10] and Cu alloys [11,12]. In the latter two references it was shown that crystallographic misorientations can arise from mechanical deformation of dendrites through fluid flow in the mushy zone.…”

Section: Introductionmentioning

confidence: 68%

Origin of intragranular crystallographic misorientations in hot-dip Al–Zn–Si coatings

Niederberger¹,

Michler²,

Jacot³

2008

Acta Materialia

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The origin of intragranular variations of the crystallographic orientation in hot-dip Al-Zn-Si coatings is discussed based on new experimental results and modelling. The solidification microstructure in as-received 55Al-43.4Zn-1.6Si (in wt.%) coatings deposited on steel plates in an industrial production line was analyzed by electron backscattered diffraction, glow-discharge optical emission spectroscopy and atomic force microscopy (AFM). The results were compared with those obtained in coatings re-solidified under different cooling and mechanical loading conditions. Continuous variations of the crystallographic orientation as large as 35°were observed within individual grains of Al-Zn-Si, consistent with previous studies. However, the mechanisms previously proposed for the origin of intragranular crystallographic misorientations had to be revisited. The new experimental data acquired during this study indicate that the solidification shrinkage accumulating in the area of the grain envelope is the driving force for the formation of intragranular misorientations. The solidification shrinkage leads to the development of tensile stresses in the oxide film covering the coating while it solidifies. Estimations based on AFM profiles and phase field simulations of the dendritic structure indicate that the stresses applied on the dendrite network are sufficient to deform plastically the dendrite arms during solidification.

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“…Eqs. [6] and [7] present the relationship found for SCN-5 wt pct CTB, where k 1 and k 2 are constants:…”

Section: Interpretation Of the Results Based On The Fragmentation mentioning

confidence: 99%

“…Dragnevski et al [6] presented a numerical flow model for dendritic solidification of strongly undercooled melt (50 K to 100 K), when both conditions for dendrite bending, high flow velocities and very fine dendrites, exist. They use a more realistic geometrical model than the analytical model of Pilling and Hellawell, [7] where the dendrites were modeled as cylinders.…”

Section: Introductionmentioning

confidence: 99%

On the Coupling Mechanism of Equiaxed Crystal Generation with the Liquid Flow Driven by Natural Convection During Solidification

Stefan-Kharicha

Kharicha

et al. 2018

Metall Mater Trans A

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The influence of the melt flow on the solidification structure is bilateral. The flow plays an important role in the solidification pattern, via the heat transfer, grain distribution, and segregations. On the other hand, the crystal structure, columnar or equiaxed, impacts the flow, via the thermosolutal convection, the drag force applied by the crystals on the melt flow, etc. As the aim of this research was to further explore the solidification-flow interaction, experiments were conducted in a cast cell (95 * 95 * 30 mm 3 ), in which an ammonium chloride-water solution (between 27 and 31 wt pct NH 4 Cl) was observed as it solidified. The kinetic energy (KE) of the flow and the average flow velocity were calculated throughout the process. Measurements of the volume extension of the mush in the cell and the velocity of the solid front were also taken during the solidification experiment. During the mainly columnar experiments (8 cm liquid height) the flow KE continuously decreased over time. However, during the later series of experiments at higher liquid height (9.5 cm), the flow KE evolution presented a strong peak shortly after the start of solidification. This increase in the total flow KE correlated with the presence of falling equiaxed crystals. Generally, a clear correlation between the strength of the flow and the occurrence of equiaxed crystals was evident. The analysis of the results strongly suggests a fragmentation origin of equiaxed crystals appearing in the melt. The transition from purely columnar growth to a strongly equiaxed rain (CET) was found to be triggered by (a) the magnitude of the coupling between the flow intensity driven by the equiaxed crystals, and (b) the release and transport of the fragments by the same flow recirculating within the mushy zone. Graphical AbstractMIHAELA STEFAN-KHARICHA, ABDELLAH KHARICHA, MENGHUAI WU, and ANDREAS LUDWIG are with the

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Mechanical deformation of dendrites by fluid flow during the solidification of undercooled melts

Cited by 69 publications

References 16 publications

The formation of regular αNi-γ(Ni31Si12) eutectic structures from undercooled Ni–25 at.% Si melts

The formation of regular αNi-γ(Ni31Si12) eutectic structures from undercooled Ni–25 at.% Si melts

Origin of intragranular crystallographic misorientations in hot-dip Al–Zn–Si coatings

On the Coupling Mechanism of Equiaxed Crystal Generation with the Liquid Flow Driven by Natural Convection During Solidification

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