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Kinetics of Phase Transformations in Steel and Aluminium studied by 3DXRD

This workshop focuses on the use of synchrotron radiation for research on structural materials, particularly in studying the kinetics of phase transformations in steel and aluminium. Topics include in-situ experiments, high spatial resolution, and time-dependent probing of individual grains.

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Kinetics of Phase Transformations in Steel and Aluminium studied by 3DXRD

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  1. Kinetics of Phase Transformations in Steel and Aluminium studied by 3DXRD Niels van Dijk (FAME/TNW/TU Delft) : N.H.vanDijk@TNW.TUDelft.NL In collaboration with: S.E. Offerman, J. Sietsma, S. van der Zwaag, N. Iqbal, L. Katgerman, G.J. Kearley TU Delft L. Margulies, S. Grigull, M.P. Moret ESRF H.F. Poulsen, E.M. Lauridsen RISØ Workshop Modern Tools for Materials Science

  2. Why use synchrotron radiation for research on structural materials ? 1. High energy large penetrating power: in-situ experiments 10% transmission thickness: @80 keV: 40 mm for Al, 5 mm for Fe @50 keV: 20 mm for Al, 2 mm for Fe @ 8 keV: 2 mm for Al, 10 m for Fe (Cu-K) 2. Small beam size high spatial resolution: individual grains beam sizes: 5 – 500 m (single crystal analysis of polycrystalline samples) 3. High intensity high sampling rate: kinetic studies exposure times: ~ 1 s sampling rate: ~ 5 s Workshop Modern Tools for Materials Science

  3. X-ray techniques Tomography 3DXRD Microscopy Imaging Recrystallisation of Al S. Schmidt et al. Science 305 (2004) 229. Solidification of Sn-Pb R.H. Mathiessen et al. Phys. Rev. Lett. 83 (1999) 5062. Granular materials: compactation S.F. Nielsen et al. Acta Materialia 51 (2003) 2407. Workshop Modern Tools for Materials Science

  4. Evolution of microstructure during phase transformations in structural materials Grain nucleation: formation of new phase grains - nm size clusters - occurs on short time scales - positioned within bulk materials - strongly dependent on interface properties Grain growth: increase in size of nucleated grain - often controlled by diffusion of alloying elements and/or heat - interaction between neighboring growing grains • dependent on microstructure of the parent phase Nucleus hard-sphere colloid S. Auer & D. Frenkel Nature 409 (2001) 1020. Need for time-dependent in-situ probe of individual grains Workshop Modern Tools for Materials Science

  5. Steel: Austenite to Ferrite Transformation Workshop Modern Tools for Materials Science

  6. Phase Transformations in Steel -Fe  -Fe + Fe3C Austenite (fcc) Ferrite (bcc) Cementite (orthorombic) • Ferrite (light) • Pearlite (dark) Pearlite = -Fe + Fe3C Workshop Modern Tools for Materials Science

  7. 3D X-Ray Diffraction Microscope 2D detector Furnace Sample w slits Bent crystal Synchrotron Beam line ID11 @ European Synchrotron Radiation Facility Workshop Modern Tools for Materials Science

  8. Diffraction pattern austenite phase • T = 900 oC • Before transformation • Beam size: 94  97 m2 • Energy = 80 keV Workshop Modern Tools for Materials Science

  9. Austenite & ferrite phase • Continuous cooling •T = 763 oC (-5 oC/min) • Half way transformation • Ferrite (red) • Austenite Workshop Modern Tools for Materials Science S.E. Offerman et al., Science 298 (2002) 1003.

  10. Phase fractions of austenite & ferrite Cooling rate: 5 oC/min Austenite ferrite Transformations: Austenite – Ferrite: A3 = 822 oC Austenite – Pearlite: A1 = 709 oC Workshop Modern Tools for Materials Science

  11. q a 100 g 75 50 total g a N 25 0 600 700 800 900 o T ( C) Number of ferrite nuclei Workshop Modern Tools for Materials Science

  12. Ferrite nucleation rate Activation energy for nucleation is orders of magnitude smaller than predicted by theory! Workshop Modern Tools for Materials Science

  13. Ferrite grain growth Growth types: Zener Continued into Pearlite C) Retarded D) Oscillatory A B C D Workshop Modern Tools for Materials Science

  14. Austenite decomposition • Carbon exchange between austenite grains • One ferrite grain per austenite • No oscillatory decomposition Workshop Modern Tools for Materials Science

  15. d d p p C C Austenite eq eq R R R n n n p p C C C C ¥ ¥ C C 0 0 Ferrite Ferrite n n C C eq eq r r R R d d c c r r n n Grain growth and decomposition model Fit-parameter: Local density of potential nuclei Workshop Modern Tools for Materials Science S.E. Offerman et al., Acta Materialia 52 (2004) 4757.

  16. Conclusions • 3DXRD gives in-situ kinetic information during transformation on: phase fraction, grain density & grain volume of individual grains • All nucleation sites are equal (in theory), but some are more equal than others (in practice) • 4 types of ferrite grain growth • 3 types of austenite grain decomposition • Ferrite growth: Transition from non-overlapping to overlapping diffusion fields Workshop Modern Tools for Materials Science

  17. Aluminium: Liquid to Solid Transformation Workshop Modern Tools for Materials Science

  18. Grain refinement of Al-Ti-B alloys pure Al pure Al + 0.03 wt.% TiB2 pure Al + 0.03 wt.% TiB2 + 0.01 wt.% solute Ti Workshop Modern Tools for Materials Science M. Easton & D. StJohn,Metall. Mater. Trans. A 30 (1999) 1629.

  19. Substrate(TiB2) Al + grain refiners Solid Liquid Workshop Modern Tools for Materials Science

  20. 3D X-Ray Diffraction Microscope E = 70 keV 2D detector Furnace Sample w slits Synchrotron Sample size : 5 mm diameter, 10 mm height Rotation angle: 1 degree Beam size: 200x200 mm Exposure time: 1 s Workshop Modern Tools for Materials Science

  21. a b c L1 L2 Liquid to Solid Phase Transformation liquid liquid + solid solid Workshop Modern Tools for Materials Science Iqbal et al., Acta Materialia 53 (2005) 2875.

  22. Transformation kinetics during solidification Sample: high purity Al + 0.1 wt.% Ti + 0.1 wt.% TiB2 Cooling rate: 1 K/min (from 973 K) Workshop Modern Tools for Materials Science

  23. Nucleation during solidification Al + TiB2 Al + Ti Al + Ti + TiB2 Workshop Modern Tools for Materials Science

  24. R(t) = S(Dt) Growth of individual aluminum grains Diffusion controlled growth: cooling rate: 1 K/min Zener theory Zener theory Workshop Modern Tools for Materials Science

  25. Al Al TiAl3 TiAl3 TiB2 TiB2 Metastable TiAl3 grains are formed before the solidification of Al starts • TiAl3 nucleates on TiB2 • Al nucleates on TiAl3 • When the Al is formed • then TiAl3 dissolves Workshop Modern Tools for Materials Science

  26. Conclusions •3DXRD gives in-situ kinetic information during transformation on: phase fraction, grain density & grain volume of individual grains • The increased nucleation during solidification of aluminum alloys is due to the metastable TiAl3 phase formed on the surface of TiB2 particles. • Grain growth in Al-Ti-B system is controlled by titanium diffusion in the beginning, by latent heat in the middle and the free growth at the end of solidification. Workshop Modern Tools for Materials Science

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