the correlations between solidification behaviors and liquid states 祖方遒 (prof fq zu) school of...
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![Page 1: The Correlations Between Solidification Behaviors And Liquid States 祖方遒 (Prof FQ ZU) School of Materials Science & Engineering](https://reader030.vdocuments.us/reader030/viewer/2022013122/56649d4a5503460f94a26bdf/html5/thumbnails/1.jpg)
The Correlations Between The Correlations Between Solidification Behaviors And Solidification Behaviors And
Liquid StatesLiquid States
祖方遒 (Prof FQ ZU)
School of Materials Science & Engineering
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Report Contents:►Background
►Brief Intro to Physical Pictures of LLST
►Effects of LLST on Solidification
►Hypothesis to the Effect of LLST
►Conclusion
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Liquid to solid transitions could be involved in most cases of the production or development of materials.
The liquid-solid correlations were recognized long before and have been intensively investigated in recent decades, chiefly focused on the effects of melt thermal history.
Although man believes liquid-solid correlations are attributed to melt structure states, the underlying nature remains uncertain and how to tune melt structures with thermal methods is still blindfold.
Background
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In recent years, some works suggest temperature induced liquid-liquid structure transitions (TI-LLST) to occur well above the liquidus in some ordinary alloys.
Here we demonstrate that TI-LLST function cruciall
y in liquid-solid correlations. The effects of TI-LLST on solidification behaviors and structures are briefly summarized as follows.
Background
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Physical Pictures of LLST
Pb-Sn61.9 isothermal experiments held at 550℃ for 72 hours
Internal friction behavior of the melt Pb-Sn61.9
Pb-Sn61.9 isothermal experiments held at 615℃
Pb-Sn melts
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Physical Pictures of LLST
In-Sn80
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ρ-T curves of the melt BiSb10 ρ-T curves of the melt SnBi40
ρ-T curves of the melt CuSn80 ρ-T curves of the melt Sn-Sb5
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Effects of LLST on Solidification:Bi-Sb10
Bi-Sb10 solidification curves from different liquid states
Solidification rate obtained by NTA method
from the melt before TI-LLST
from the melt after TI-LLST
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Alloy Sn-Bi40 Bi-Sb10 Sn-Sb42 Cu-Sn80
TI-LLSTTemperature range
762-950°C 805-1065°C No TI-LLSTdetected
702-776°C
Reversibility no no — yes
Melt states withDifferent procedures
A 650°C 700°C 700°C 700°C
B 1000-650°C 1100-700°C 850-700°C 810-700°C
C — — 850°C 810°C
Under-cooling/°C
A△ TL=3.8
△ TE=2.8△ TL=13.1
△TL=2.9
△T(β)=2.8
△TL=19.8
△TE=3.1
B△ TL=25.3
△ TE=6.6△ TL=18.9
△TL=2.8
△T(β)=3.4
△TL=19.6
△TE=2.8
C — —△TL=2.6
△T(β)=2.9
△TL=22.8
△TE=8.2
Different melt Procedures and the effect on Undercooling
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Pb26Sn42Bi32
SnBi40
from the melt before TI-LLST from the melt after TI-LLST
primary β-Sn: 50% to 35%
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Effect of LLST OR Melt Over-heating?
(a) melted at 700°C-60min
(b) melted with 950°C-60min+700°C-30min
Sn-Sb42 without TI-LLST detected
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The cases with reversible TI-LLST :
Solidified structures of Cu-Sn80 with different melt procedures
(a ) melted at 700°C-60min,( b ) melted with810°C-60min+700°C-30min,
(C ) melted at 810°C-60min
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LLST Effect on Phase selection & Growth Manner
[015]
Bi-40Te Structures solidified from the melt
(680 )℃
Bi-40Te Structures solidified from the melt
(780 )℃
the amount of peritectic phase has increased fro
m 30.6% to 56.4%
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Enlarged Undercooling and Higher Nucleation Rate
• On solidification, with the microstructures of clusters analogous to solid phases before TI-LLST, the melts are more prone to either heterogeneous or homogeneous nucleation when temperature is below the liquidus. After alloy melts experienced TI-LLST, however, it is harder to nucleate because the smaller and more homogeneous clusters are distinct from solid phases, so that it should go lower temperature to nucleate with a larger undercooling, and a higher nucleation rateis obtained.
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Hypothesis
bG
CG
mG
bG
thermodynamic model near the liquid-solid interface during
solidification:
the energy barrier to overcome for liquid-to-solid transfer of melt clusters before/without TI-LLST,
for the melt having experienced TI-LLST, an additional energy barrier to overcome for resetting atoms from the distinct arrangement of the clusters to lattice sites of the growing crystal after the initial attachment,
+ the energy barrier to overcome for solid-to-liquid transfer of
melt clusters.
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Change of Growth Rate: R
The net transfer frequency net
)/exp(1)/exp(0 KTGKTG mBnet without TI-LLST
)/exp(1/)(exp' 0 KTGKTGG mCBnet after TI-LLST
the growing rate R= net
RR 'netnet '
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the effective partition coefficient
RKTGGakf
RKTGakfK
mbSS
bLLE
/)(exp
/exp
0
0
'/)(exp
'/)(exp'
0
0
RKTGGakf
RKTGGakfK
mbSS
CbLLE
without TI-LLST
after TI-LLST
EE KK '
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ConclusionThe liquid-solid correlations in respect of liquid thermal history, in essence, rests on whether and how LLST to occur.
If TI-LLST occurs and is not reversible, it brings about different liquid states and results in alterations to solidification behaviors with higher nucleation rates and the altered solute redistribution process, therefore also to solidification structures such as the grain size and crystal configurations, and even to the phase selection
If a liquid system without TI-LLST, the liquid thermal history has no influence on solidification because it results in no different liquid state.
if TI-LLST is reversible, then the liquid-solid correlations are dependent on whether the reverse process could be prevented after TI-LLST in manipulating melt thermal history.
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Thank You !