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Dierk Raabe T W I P Steel 2009 M S T
1. Interface-related micromechanics in TWIP steels
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe
28. October 2009, MS&T, Pittsburgh
Acknowledgements:
SFB 761 “Steel ab initio”;
discussions with Marty Crimp and Tom Bieler
(Michigan State University)
see also: talk at 2 pm Thursday room 328, EBSD session
6. 5
Scaling issue in microscopy
?
TEM EBSD
EBSD orientation contrast
is not lattice defect contrast
Large scale mapping of lattice
defects
TEM information in SEM
Electron Channeling Contrast Imaging
Example: Fe-22Mn-0.6C (wt%), TWIP
7. 6
EBSD
High spatial and
angular resolution
ECCI
1 nm
10 nm
100 nm
1000 nm
0.001º 0.01º 0.1º 1º
Spatial
resolution
Angular
resolution
Limited spatial and
angular resolution
Good spatial and
angular resolution
TEM
Overview characterization
8. Electron channeling contrast mechanism
Dislocation imaging
[A.J. Wilkinson, P.B. Hirsch, Micron 28 (1997) 279]
Requirement: Crystal at Bragg condition
Imaging under controlled diffraction conditions
9. 8
Fe-22Mn-0.6C (wt%) TWIP steel
High resolution EBSD ECCI
twins
Dislocation cells
Comparison EBSD-ECCI
Electron Channeling Contrast Imaging
12. 11
ECCI / SEM
(-220)
Dislocation cells are clearly seen by ECCI
TEM-Bright Field
Fe-22Mn-0.6C (wt%) TWIP steel
Electron Channeling Contrast Imaging
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740
13. 12
0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stress
Hardening (MPa)
Hardening/Stress(MPa)
True strain
YS: 210 MPa
UTS: 1200 MPa
Ductility: 51%
strain rate: 2.5x10-4 s-1
tensile test, room temperature
10%
20%
40%
TA
twins
TA
step size: 50 nm
twins do not provide much
strain but the 2nd
hardening plateau
EBSD: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740
15. 2nd hardening stage:
2%<e< 10%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
17. 3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
19. 5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
20. Type I
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
21. Type II
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
22. Type III
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
23. 0
20
40
60
80
100
0.05 0.1 0.2 0.4
DDW+Cells
DDW+Cells+Twins
Type I
Type II
Type III
%
True strain
Type of grain
Interface statistics
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
24. Most of the grains follow
the Schmid’s Law (3/4)
True strain: 40%
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
25. True strain: 40%
Some of the grains follow
the Schmid’s Law
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
26. True strain: 40%
1-2activated twinning
systems nucleated at
grain boundaries
No twins inside the grain (few degrees from [001])
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
27. Grains with “low” twinning activity:
-Short twins (less than 5 microns length)
-Few twins
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
28. Grains with “high” twinning activity:
-Long twins
-Thick bundles of twins
-High population of twins
These results suggest a
Sslip/Stwinning relationship
on twin growth
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
29. Type I
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
30. Type II
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
31. Type III
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
32. 31
Fe22Mn0.6C TWIP steel
Mechanical twins
Dislocation cells
Electron Channeling Contrast Imaging
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
33. EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
35. 34
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe: Scripta Mater. 61 (2009) 737-740
Electron channeling contrast imaging of twins and dislocations in twinning-
induced plasticity steels under controlled diffraction conditions in a scanning
electron microscope
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe: Mater. Sc. Engin. A 527 (2010)
3552-3560
The effect of grain size and grain orientation on deformation twinning in a
Fe–22 wt.% Mn–0.6 wt.% C TWIP steel
References