Post on 10-Mar-2020
transcript
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
2
Stress Corrosion Cracking
How it’s done: Misorientations Deformation
3
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
4
SSD SSD + GND
Misorientations ”Invisible”
Deformation
Dislocations
Misorientation Hardness
Misorientations – Hardness
5
High GND – Hard?
Low GND – Soft?
Approach
6
Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
Approach
7
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
8
Approach
9
Deform Material SSD + GND
Misorientation map
Material Hardness Hardness map by Nanoindentation
Deformation map
Predicted Hardness map
Deformation Strength
10
Necking
Deformation Strength
11
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
12
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
13
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
14
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
16
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
17
20 µm
Comparison
18
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
19
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
20
20 µm
20 µm
More comparison
21
Our explanation
22
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
23
Questions?