1. The Correlations Between Solidification Behaviors And Liquid States 祖方遒 (Prof FQ ZU) School of Materials Science & Engineering

2. Report Contents: ► Background ► Brief Intro to Physical Pictures of LLSTLLST ►Effects of LLST on Solidification ►Hypothesis to the Effect of LLST ► Conclusion

3.  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

4.  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 crucially in liquid-solid correlations. The effects of TI-LLST on solidification behaviors and structures are briefly summarized as follows. Background

5. 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

6. Physical Pictures of LLST In-Sn80

7. 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

8. 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

9. AlloySn-Bi40Bi-Sb10Sn-Sb42Cu-Sn80 TI-LLST Temperature range 762-950°C805-1065°CNo TI-LLST detected 702-776°C Reversibilityno —yes Melt states with Different procedures A650°C700°C B 1000 - 650°C1100 - 700°C850 - 700°C810 - 700°C C——850°C810°C Under-cooling / °C A △ T L =3.8 △ T E =2.8 △ T L =13.1 △ T L =2.9 △ T(β)=2.8 △ T L =19.8 △ T E =3.1 B △ T L =25.3 △ T E =6.6 △ T L =18.9 △ T L =2.8 △ T(β)=3.4 △ T L =19.6 △ T E =2.8 C—— △ T L =2.6 △ T(β)=2.9 △ T L =22.8 △ T E =8.2 Different melt Procedures and the effect on Undercooling

10. Pb26Sn42Bi32 SnBi40 from the melt before TI-LLSTfrom the melt after TI-LLST primary β-Sn : 50% to 35%

11. 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

12. 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

13. 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 from 30.6% to 56.4%

14. 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.

15. Hypothesis 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.

16. Change of Growth Rate: R The net transfer frequency without TI-LLST after TI-LLST the growing rate R=

17. the effective partition coefficient without TI-LLST after TI-LLST

18. Conclusion The 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.

19. Thank You !