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 November 10, 2018 Workshop Modern Tools for Materials Science

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

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

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

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

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

3D X-Ray Diffraction Microscope 2D detector Furnace Sample w slits Bent crystal Synchrotron Beam line ID11 @ European Synchrotron Radiation Facility November 10, 2018 Workshop Modern Tools for Materials Science

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

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.

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

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

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

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

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

Grain growth and decomposition model eq 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.

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

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

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 November 10, 2018 Workshop Modern Tools for Materials Science M. Easton & D. StJohn, Metall. Mater. Trans. A 30 (1999) 1629.

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

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

Liquid to Solid Phase Transformation b c L1 L2 liquid liquid + solid solid November 10, 2018 Workshop Modern Tools for Materials Science Iqbal et al., Acta Materialia 53 (2005) 2875.

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

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

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

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

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