Validity of EBSD plastic strain estimation on a …/Shen...Validity of EBSD plastic strain...
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Validity of EBSD plastic strain estimation on a microstructural size scale Rickard Shen, Valter Ström and Pål Efsing SKC Symposium October 8-9, 2015, Sigtuna, Sweden
Transcript of Validity of EBSD plastic strain estimation on a …/Shen...Validity of EBSD plastic strain...
Validity of EBSD plastic strain estimation on a microstructural size scale Rickard Shen, Valter Ström and Pål Efsing
SKC Symposium
October 8-9, 2015, Sigtuna, Sweden
Deformation
Alloy 690 susceptible to SCC after cold work
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Stress Corrosion Cracking
How it’s done: Misorientations Deformation
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True Strain0 0.05 0.1 0.15M
isorie
ntat
ion
[°]
0
0.2
0.4
True Strain0 0.05 0.1 0.15Tr
ue S
tres
s [M
Pa]
0
200
400
600
How deformation causes misorientations
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SSD SSD + GND
Misorientations ”Invisible”
Deformation
Dislocations
Misorientation Hardness
Misorientations – Hardness
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High GND – Hard?
Low GND – Soft?
Approach
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Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
Approach
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Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
True Strain0 0.05 0.1 0.15M
isorie
ntat
ion
[°]
0
0.2
0.4
True Strain0 0.05 0.1 0.15Tr
ue S
tres
s [M
Pa]
0
200
400
600
How it’s done: Misorientations Deformation
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Approach
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Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
Deformation Strength
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Necking
Deformation Strength
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True strain0 0.1 0.2 0.3 0.4 0.5 0.6
True
stre
ss [M
Pa]
0
250
500
750
1000
1250
1500
Experiment
Ludwik model: 278 + 1550·p0.806
Berkovitch Indenter adds 0.08 strain
Deformation Hardness
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True strain0 0.1 0.2 0.3 0.4 0.5 0.6
True
stre
ss [M
Pa]
0
250
500
750
1000
1250
1500
Experiment
Ludwik model: 278 + 1550·p0.806
+Berkovitch indentation strain of 0.08
Tabor: H ≈ 3σ
Deformation Hardness
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True strain0 0.2 0.4 0.6
Hard
ness
[GPa
]
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
H = 3·[278 + 1550·( p +0.08)0.806
]
Vickers Hardness tests
0.77
0.00
True
Str
ain
20 µm
Deformation Hardness
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True strain0 0.2 0.4 0.6
Hard
ness
[GPa
]
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
H = 3·[278 + 1550·( p +0.08)0.806
]
Vickers Hardness tests
4.35
1.44
Pred
icte
d Ha
rdne
ss [G
Pa]
20 µm
Approach
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Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
Nanoindentation
Tip: Berkovich Depth: 100 nm C–C spacing: 2.6 µm Load: ~1.8–2.0 mN Dwell time: 20 s Load rate: 0.05 mN/s
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20 µm
Comparison
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Hardness profile well captured: 1. Band of high hardness 2. Low in upper corners 3. Medium in lower left
1 2 2
3
20 µm
Different scale bars
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4.35 [GPa]
1.44 [GPa]
3.20 [GPa]
2.60 [GPa]
Factor ~1.2 of lowest values
Factor ~3 of lowest values
More comparison
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20 µm
20 µm
More comparison
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Our explanation
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Disl
ocat
ion
Dens
ity
Position
Both show the same
profile
Hardness relies on SSD+GND Variations seem small
Misorientations relies on GND Variations seem large
High uniform SSD
Conclusions
• Typical misorientation strain method: • Can capture trends of strain/hardness • Cannot quantify strain/hardness
• High uniform SSD density • Low misorientation ≠ Low strain
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Questions?
