1. Kinetics of Phase Transformations
in Steel and Aluminium studied by 3DXRD
Niels van Dijk (FAME/TNW/TU Delft) :
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
November 10, 2018
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
November 10, 2018
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.
November 10, 2018
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
November 10, 2018
Workshop Modern Tools for Materials Science

5. Steel: Austenite to Ferrite Transformation
November 10, 2018
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
November 10, 2018
Workshop Modern Tools for Materials Science

7. 3D X-Ray Diffraction Microscope
2D detector
Furnace
Sample w
slits
Bent crystal
Synchrotron
Beam line European Synchrotron Radiation Facility
November 10, 2018
Workshop Modern Tools for Materials Science

8. Diffraction pattern austenite phase
• T = 900 oC
• Before transformation
• Beam size: 94  97 m2
• Energy = 80 keV
November 10, 2018
Workshop Modern Tools for Materials Science

9. Austenite & ferrite phase
• Continuous cooling
• T = 763 oC (-5 oC/min)
• Half way transformation
• Ferrite (red)
• Austenite
November 10, 2018
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
November 10, 2018
Workshop Modern Tools for Materials Science

11. T ( C) N 600 700 800 900 25 50 75 100 Number of ferrite nuclei q g a25 50 75
100
T ( o C) N
total
November 10, 2018
Workshop Modern Tools for Materials Science

12. Ferrite nucleation rate
Activation energy for
nucleation is orders
of magnitude smaller
than predicted by
theory!
November 10, 2018
Workshop Modern Tools for Materials Science

13. Ferrite grain growth Growth types: Zener Continued into Pearlite
C) Retarded
D) Oscillatory A B C D
November 10, 2018
Workshop Modern Tools for Materials Science

14. Austenite decomposition
• Carbon exchange
between austenite
grains
• One ferrite grain
per austenite
• No oscillatory
decomposition
November 10, 2018
Workshop Modern Tools for Materials Science

15. Grain growth and decomposition modeleq d c
Ferrite
Austenite
Fit-parameter:
Local density of potential nuclei
November 10, 2018
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
November 10, 2018
Workshop Modern Tools for Materials Science

17. Aluminium: Liquid to Solid Transformation
November 10, 2018
Workshop Modern Tools for Materials Science

18. Grain refinement of Al-Ti-B alloys
pure Al
pure Al
wt.% TiB2
pure Al
wt.% TiB2
wt.% solute Ti
November 10, 2018
Workshop Modern Tools for Materials Science
M. Easton & D. StJohn, Metall. Mater. Trans. A 30 (1999) 1629.

19. Al + grain refiners Liquid Solid
Substrate(TiB2)
Solid
Liquid
November 10, 2018
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
November 10, 2018
Workshop Modern Tools for Materials Science

21. Liquid to Solid Phase Transformationb c L1 L2
liquid
liquid + solid
solid
November 10, 2018
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)
November 10, 2018
Workshop Modern Tools for Materials Science

23. Nucleation during solidification
Al + TiB2
Al + Ti
Al + Ti + TiB2
November 10, 2018
Workshop Modern Tools for Materials Science

24. Growth of individual aluminum grains R(t) = S(Dt)
Diffusion controlled growth:
cooling rate: 1 K/min
Zener
theory
Zener
theory
November 10, 2018
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
November 10, 2018
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.
November 10, 2018
Workshop Modern Tools for Materials Science