Evidence of recrystallization mechanism of grain refinement in hypercooled Co80Pd20 alloys

Xu, Xiaolong; Chen, Y.Z.; Liu, F.

doi:10.1016/j.matlet.2012.04.042

Cited by 36 publications

(18 citation statements)

References 19 publications

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“…Besides, at the undercooling value ∆T*(V D ), the remelted fraction reaches zero and no chemical superheating induced dendrite remelting will happen. Thus, as previous study [10][11][12][13][14][15][16][17][18] showing, the grain refinement above the second critical undercooling ∆T* is induced by the mechanisms of stress-induced breakup and recrystallization of the rapidly solidified dendrites, rather than dendrite remelting induced by chemical superheating, which can hardly affect the dendrite breakup in the high undercooling range as shown in Figure 7. Obviously, the significance of the present extended chemical superheating model is that it can predict good results in consistency with the experiment observation and the relaxation effect on non-equilibrium solidification of undercooled melt is clearly illustrated.…”

Section: Grain Refinement Mechanism Of First Refinementsupporting

confidence: 64%

“…We also have revealed this phenomenon in hypercooled Co-20at.%Pd alloys and found strong and direct evidences, see Ref. [13].…”

Section: Stress Induced Recrystallization Mechanism (δT > δT*)mentioning

confidence: 61%

“…Firstly, we need to use the BCT model by Boettinger, Coriell and Trividi [13] to calculate the solidification parameters. According to the models, the initial undercooling ΔT at the dendrite tip consists of four parts,…”

Section: Dendrite Growth Analysismentioning

confidence: 99%

“…It is well known that [13][14][15], in a single phase alloy, the condition of diffusional equilibrium is gradually becoming less important with the increase of solidification velocity and undercooling in front of the dendrite tip. Therefore, solute rejection is reduced and solutal undercooling decreases as the interface concentration approaches the melt composition.…”

Section: Dendrite Growth Analysismentioning

confidence: 99%

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Rapid Solidification of Undercooled Melts

Xu¹,

Hou²,

Liu³

2018

Solidification

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Rapid solidification and microstructure evolution of deeply undercooled bulk concentrated Ni-20%at.Cu and Co-20%at.Pd alloys are strictly and systematically evaluated. First, thermodynamics of the undercooled melt is discussed. Consideration is provided for not only the systematic microstructure evolution within a broad undercooling range, but also the dendrite growth mechanism and the rapid solidification characteristics. The dendrite growth in the bulk undercooled melts was captured by a high speed camera. The first kind of grain refinement occurring in the low undercooling regimes was explained by a current grain refinement model. Besides for the dendrite melting mechanism, the stress originating from the solidification contraction and thermal strain in the first mushy zone during rapid solidification could be a main mechanism causing the second kind of grain refinement above the critical undercooling. This internal-stress led to the distortion and breakup of the primary dendrites and was semi-quantitatively described by a corrected stress accumulation model. It was found that the stress induced recrystallization could make the primary microstructures refine substantially after recalescence.

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Section: Grain Refinement Mechanism Of First Refinementsupporting

confidence: 64%

“…We also have revealed this phenomenon in hypercooled Co-20at.%Pd alloys and found strong and direct evidences, see Ref. [13].…”

Section: Stress Induced Recrystallization Mechanism (δT > δT*)mentioning

confidence: 61%

Section: Dendrite Growth Analysismentioning

confidence: 99%

Section: Dendrite Growth Analysismentioning

confidence: 99%

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Rapid Solidification of Undercooled Melts

Xu¹,

Hou²,

Liu³

2018

Solidification

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“…One expected consequence of this would be that grains arising from neighbouring seaweed branches would have similar, but not identical crystallographic orientations, which in the as-solidified sample would lead to a high density of low-angle grain boundaries (LAGB). Recent analysis of undercooled Co-Pd [55] and Ni-Pd [54,56] alloys by Xu et al found just such evidence for a high density of LAGB's, although they took this as being evidence for a recrystallisation mechanism for grain refinement, rather than remelting, on the assumption that the underlying structure preceding remelting was dendritic. However, their result would be consistent with a remelting model if the original solidification structure prior to remelting were seaweed, rather than conventional dendrites.…”

Section: Discussionmentioning

confidence: 99%

The Origins of Spontaneous Grain Refinement in Deeply Undercooled Metallic Melts

Mullis

2014

Metals

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Phase-field modeling of rapid alloy solidification, in which the rejection of latent heat from the growing solid cannot be ignored, has lagged significantly behind the modeling of conventional casting practices which can be approximated as isothermal. This is in large part due to the fact that if realistic materials properties are adopted, the ratio of the thermal to solute diffusivity (the Lewis number) is typically 10 3 -10 4 , leading to severe multi-scale problems. However, use of state-of-the-art numerical techniques, such as local mesh adaptivity, implicit time-stepping and a non-linear multi-grid solver, allow these difficulties to be overcome. Here we describe how the application of such a model, formulated in the thin-interface limit, can help to explain the long-standing phenomenon of spontaneous grain refinement in deeply undercooled melts. We find that at intermediate undercoolings the operating point parameter, σ*, may collapse to zero, resulting in the growth of non-dendritic morphologies such as doublons and 'dendritic seaweed'. Further increases in undercooling then lead to the re-establishment of stable dendritic growth. We postulate that remelting of such seaweed structures gives rise to the low undercooling instance of grain refinement observed in alloys.

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Recalescence Velocity and Microstructure Evolution of Deeplyundercooled Cu65Ni35 Alloy

Liang

Tang

et al. 2022

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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Evidence of recrystallization mechanism of grain refinement in hypercooled Co80Pd20 alloys

Cited by 36 publications

References 19 publications

Rapid Solidification of Undercooled Melts

Rapid Solidification of Undercooled Melts

The Origins of Spontaneous Grain Refinement in Deeply Undercooled Metallic Melts

Recalescence Velocity and Microstructure Evolution of Deeplyundercooled Cu65Ni35 Alloy

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