Change of the kinetics of solidification and microstructure formation induced by convection in the Ni–Al system

Reutzel, S.; Hartmann, H.; Galenko, Peter; Schneider, Stephan; Herlach, D.M.

doi:10.1063/1.2760154

Cited by 59 publications

(43 citation statements)

References 10 publications

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“…However, the critical velocity observed here is consistent with the growth velocity of fully ordered superlattice structures, maximum values for which are given in [26] as being in the range from 0.2 to 0.5 m s -1 . In contrast, the critical velocities observed in the systems CoSi and Fe 3 Ge discussed above are significantly in excess of these values, particularly in the case of CoSi, which is also a congruently melting compound.…”

Section: Resultssupporting

confidence: 71%

“…As such, it is a potentially simple system in which to study the transition from ordered to disordered growth with increasing departures from equilibrium. Growth velocity measurements made on a Ni-24at.% Ge alloy over the undercooling range 57 K ≤ ΔT ≤ 362 K appear to indicate that this material does indeed undergo a transition from slow, diffusion limited, growth to much more rapid, collision limited growth, with the critical undercooling for this transition being ΔT = 168 K. The growth velocity at this critical undercooling is ≈ 0.22 m s -1 , much lower than reported in other ordered intermetallics [8,20,21], but consistent with expected diffusive velocities in fully ordered superlattice structures [26]. The maximum growth velocity recorded in this material was 3.55 m s -1 .…”

Section: Resultsmentioning

confidence: 67%

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Disorder trapping during the solidification of βNi3Ge from its deeply undercooled melt

Ahmad

Mullis

2011

J Mater Sci

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A melt encasement (fluxing) technique has been used to solidify the congruently melting intermetallic βNi 3 Ge from its deeply undercooled parent melt. High speed photography and a photo-diode technique have been used to measure the resulting growth velocity. The maximum undercooling achieved was 362 K, wherein a growth velocity of 3.55 m s -1 was recorded. At an undercooling of 168 K an abrupt increase in the gradient of the velocity-undercooling curve is observed and this is attributed to a transition from growth of the ordered L1 2 compound at low undercooling, to growth of the fully disordered compound at high undercooling. A change in the microstructure, from a distribution of very coarse (700 μm), randomly oriented grains to a fine grained structure (15-20 μm) with a large number of low angle grain boundaries is observed coincident with this transition in the velocity-undercooling curve, a grain refinement pattern that is different to that observed either in deeply undercooled solid solutions or other intermetallics. This transition is ascribed to a recovery and recrystallisation process in the disordered phase due to the low post-recalescence cooling rate.

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Section: Resultssupporting

confidence: 71%

Section: Resultsmentioning

confidence: 67%

Disorder trapping during the solidification of βNi3Ge from its deeply undercooled melt

Ahmad

Mullis

2011

J Mater Sci

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“…Al 50 Ni 50 was chosen for the investigations on growth kinetics under the conditions of forced convection on Earth and reduced convection in reduced gravity [43]. This alloy melts congruently and forms an intermetallic B2 β-phase under equilibrium conditions.…”

Section: Influence Of Forced Convection On Dendrite Growth Kineticsmentioning

confidence: 99%

Non-Equilibrium Solidification of Undercooled Metallic Melts

Herlach

2014

Metals

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Abstract:If a liquid is undercooled below its equilibrium melting temperature an excess Gibbs free energy is created. This gives access to solidification of metastable solids under non-equilibrium conditions. In the present work, techniques of containerless processing are applied. Electromagnetic and electrostatic levitation enable to freely suspend a liquid drop of a few millimeters in diameter. Heterogeneous nucleation on container walls is completely avoided leading to large undercoolings. The freely suspended drop is accessible for direct observation of rapid solidification under conditions far away from equilibrium by applying proper diagnostic means. Nucleation of metastable crystalline phases is monitored by X-ray diffraction using synchrotron radiation during non-equilibrium solidification. While nucleation preselects the crystallographic phase, subsequent crystal growth controls the microstructure evolution. Metastable microstructures are obtained from deeply undercooled melts as supersaturated solid solutions, disordered superlattice structures of intermetallics. Nucleation and crystal growth take place by heat and mass transport. Comparative experiments in reduced gravity allow for investigations on how forced convection can be used to alter the transport processes and design materials by using undercooling and convection as process parameters.

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“…[8] in relation to the B2 AlNi phase, and [9] in relation to CoSi) that growth of the ordered phase is significantly slower than that of the disordered phase, with a jump in the growth velocity being evident at the (1 st order) disorder-order transition. In a previous paper Ahmed et al [10] studied disorder trapping in the congruently melting compound -Ni3Ge using a flux undercooling technique.…”

Section: Introductionmentioning

confidence: 99%

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

Haque

Mullis

2016

Intermetallics

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Single-phase -Ni3Ge has been rapidly solidified via drop-tube processing. At low cooling rates (850 -300 m diameter particles, 700 -2800 K s -1 ) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates (300 -75 m diameter particles, 2800 -25000 K s -1 ) the dominant solidification morphology is that of dendrites, again imbedded within a featureless matrix. As the cooling rate increases towards the higher end of this range the dendrites display non-orthogonal side-branching and tip splitting. At the highest cooling rates studied (< 75 m diameter particles, > 25000 K s -1 ), dense-branched fractal structures are observed. Selected area diffraction analysis in the TEM reveals the spherulites and dendrites are a disordered variant of -Ni3Ge, whilst the featureless matrix is the ordered variant of the same compound. We postulate that the spherulites and dendrites are the rapid solidification morphology and that the ordered, featureless matrix grew more slowly post-recalescence. Spherulites are most likely the result of kinetically limited growth, switching to thermal dendrites as the growth velocity increases. It is extremely uncommon to observe such a wide range of morphologies as a function of cooling rate in a single material.

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Change of the kinetics of solidification and microstructure formation induced by convection in the Ni–Al system

Cited by 59 publications

References 10 publications

Disorder trapping during the solidification of βNi3Ge from its deeply undercooled melt

Disorder trapping during the solidification of βNi3Ge from its deeply undercooled melt

Non-Equilibrium Solidification of Undercooled Metallic Melts

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

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