the correlations between solidification behaviors and liquid states

19
The Correlations The Correlations Between Solidification Between Solidification Behaviors And Liquid Behaviors And Liquid States States 祖祖祖 (Prof FQ ZU) School of Materials Science & En gineering

Upload: cheche

Post on 13-Jan-2016

24 views

Category:

Documents


1 download

DESCRIPTION

The Correlations Between Solidification Behaviors And Liquid States. 祖方遒 (Prof FQ ZU) School of Materials Science & Engineering. Report Contents:. Background Brief Intro to Physical Pictures of LLST Effects of LLST on Solidification Hypothesis to the Effect of LLST Conclusion. - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: The Correlations Between Solidification Behaviors And Liquid States

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

Page 2: The Correlations Between Solidification Behaviors And Liquid States

Report Contents:►Background

►Brief Intro to Physical Pictures of LLST

►Effects of LLST on Solidification

►Hypothesis to the Effect of LLST

►Conclusion

Page 3: The Correlations Between Solidification Behaviors And Liquid States

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

Page 4: The Correlations Between Solidification Behaviors And Liquid States

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

Page 5: The Correlations Between Solidification Behaviors And Liquid States

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

Page 6: The Correlations Between Solidification Behaviors And Liquid States

Physical Pictures of LLST

In-Sn80

Page 7: The Correlations Between Solidification Behaviors And Liquid States

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

Page 8: The Correlations Between Solidification Behaviors And Liquid States

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

Page 9: The Correlations Between Solidification Behaviors And Liquid States

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

Page 10: The Correlations Between Solidification Behaviors And Liquid States

Pb26Sn42Bi32

SnBi40

from the melt before TI-LLST from the melt after TI-LLST

primary β-Sn: 50% to 35%

Page 11: The Correlations Between Solidification Behaviors And Liquid States

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

Page 12: The Correlations Between Solidification Behaviors And Liquid States

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

Page 13: The Correlations Between Solidification Behaviors And Liquid States

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%

Page 14: The Correlations Between Solidification Behaviors And Liquid States

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.

Page 15: The Correlations Between Solidification Behaviors And Liquid States

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.

Page 16: The Correlations Between Solidification Behaviors And Liquid States

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 '

Page 17: The Correlations Between Solidification Behaviors And Liquid States

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 '

Page 18: The Correlations Between Solidification Behaviors And Liquid States

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.

Page 19: The Correlations Between Solidification Behaviors And Liquid States

Thank You !