dierk raabe t w i p steel 2009 m s t
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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
Overview
Motivation
Characterization of interfaces in TWIP
Strain hardening behavior in TWIP
Conclusions
Dierk Raabe, MS&T, Pittsburgh, 28. Oct. 2009, MPIE
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tota
l elo
ngatio
n to f
ract
ure
[%
]
ultimate tensile strength [MPa]
TRIP and complex phaseTRIP and complex phase
martensiticmartensitic
maraging TRIPmaraging TRIP
dual phasedual phase
ferriticferritic
Ductility-strength profile for sheet steels
austenitic stainlessaustenitic stainless
advanced TWIP and TRIP
advanced TWIP and TRIP
www.mpie.de
www.mpie.de
www.mpie.de
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200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 16000
10
20
30
40
50
60
70
80
tota
l elo
ngatio
n to f
ract
ure
[%
]
ultimate tensile strength [MPa]
TRIP and complex phaseTRIP and complex phase
martensiticmartensitic
maraging TRIPmaraging TRIP
dual phasedual phase
ferriticferritic
Ductility-strength profile for sheet steels
austenitic stainlessaustenitic stainless
advanced TWIP and TRIP
advanced TWIP and TRIP
Characterization
TEM, EBSD
High spatial resolution EBSD
3D EBSD (joint 2D EBSD plus serial sectioning)
Electron channeling contrast imaging (ECCI)
ECCI combined with EBSD: ECCI under controlled diffraction conditions
Dierk Raabe, MS&T, Pittsburgh, 27. Oct. 2009, MPIE
6
Scaling issue in microscopy
?TEM EBSD
EBSD orientation contrastis not lattice defect contrast
Large scale mapping of lattice defects
TEM information in SEM
EBSD orientation contrastis 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
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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
Electron channeling contrast mechanism
Dislocation imaging
[A.J. Wilkinson, P.B. Hirsch, Micron 28 (1997) 279]
Requirement: Crystal at Bragg conditionImaging under controlled diffraction conditions
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Fe-22Mn-0.6C (wt%) TWIP steel
High resolution EBSD ECCItwins
Dislocation cells
Comparison EBSD-ECCI
Electron Channeling Contrast Imaging
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SEM
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SEM
TEM
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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
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0 0.1 0.2 0.3 0.4 0.5
True stressHardening (MPa)
Har
deni
ng/
Str
ess
(MP
a)
True strain
YS: 210 MPaUTS: 1200 MPaDuctility: 51%strain rate: 2.5x10-4 s-1
tensile test, room temperature10%
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
0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stressHardening (MPa)
Har
den
ing/
Str
ess
(MP
a)
True strain
YS: 210 MPaUTS: 1200 MPaDuctility: 51%strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
2nd hardening stage:
2%<e< 10%
-Planar slip structures + wavy structures-Few mechanical twins*
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740
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
0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stressHardening (MPa)
Har
den
ing/
Str
ess
(MP
a)
True strain
YS: 210 MPaUTS: 1200 MPaDuctility: 51%strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
3rd hardening stage:
10%<e< 25%
-Wavy structures: dislocation cells-Mechanical twins-3 Types of grains
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
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
0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stressHardening (MPa)
Har
den
ing/
Str
ess
(MP
a)
True strain
YS: 210 MPaUTS: 1200 MPaDuctility: 51%strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
5th hardening stage:
35%<e< 50%
-Wavy structures: dislocation cells-Mechanical twins-3 Types of grains
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
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
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
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
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
0
20
40
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80
100
0.05 0.1 0.2 0.4
DDW+CellsDDW+Cells+TwinsType IType IIType III
%
True strain
Type of grain
Interface statistics
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
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
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
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
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
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
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
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
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
32Fe22Mn0.6C TWIP steel
Mechanical twins
Dislocation cells
Electron Channeling Contrast Imaging
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552
Set-up is proposed for ECCI under controlled diffraction conditions by means of EBSD in conventional FEG-SEM
Two positions set-up: low-tilt position for ECCI (high-tilt position (70º) for EBSD; optimized operation conditions: small working distance (<7 mm) and 10 kV
Dislocation cells and mechanical twins of 20 nm in thickness are imaged in a deformed TWIP steel
The ECCI technique under controlled diffraction conditions is a powerful tool for characterizing deformed bulk materials
Interface statistics in TWIP at different deformation regimes
Hall Petch parameter for twin-dislocation interaction below that for g.b.-dislocation interaction
Dierk Raabe, MS&T, Pittsburgh, 27. Oct. 2009, MPIE
Summary
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I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe: Scripta Mater. 61 (2009) 737-740Electron 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