Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains
description
Transcript of Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains
Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains
Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains
Thomas Gnäupel-Herold1,2,Adam Creuziger, T.Foecke3
1University of Maryland2NIST Center for Neutron Research
3NIST Metallurgy Division
Thomas Gnäupel-Herold1,2,Adam Creuziger, T.Foecke3
1University of Maryland2NIST Center for Neutron Research
3NIST Metallurgy Division
Formability: strain localization on grain
boundaries
Formability: strain localization on grain
boundaries
up to 0.5 mm displacement found between neighboring grains
BCC Crystal Structure< 111 > slip direction (close-packed direction)
Any plane containing < 111 > is a potential slip plane
Experimentally observed in (110), (112) & (123) planes
Plastic Properties of Niobium
Plastic Properties of Niobium
Tensile TestsOrientations
Tensile TestsOrientations
Tensile TestsTensile Tests
0
50
100
150
200
250
0 0.2 0.4 0.6 0.8 1
strain
tru
e st
ress
[M
Pa]
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S12
S13
S14
S15
1 0 0 1 1 0
1 1 1
S1
S2
S3
S4
S5
S6
S7
S8
S9S10
S12 S13
S14
S16
S17
Yield StressYield StressYield Stress
0
20
40
60
80
100
120
140
160
g1
g2
g3
g4
g5
g6
g7
g8
g9
g1
0
g1
2
g1
3
g1
4
g1
5
P1
P2
P3
Specimen
s0.
2 [
MP
a]
Single crystal
Polycrystal
YS between 25 MPa and 40 MPa
weak anisotropy
25% YS of poly-crystal
YS between 25 MPa and 40 MPa
weak anisotropy
25% YS of poly-crystal
R-ValuesR-Values
Extreme anisotropy from r=0 (thinning only) to r>1 (no thinning)
Polycrystal r=0.1 Large r-values for
{210}<-120>
Extreme anisotropy from r=0 (thinning only) to r>1 (no thinning)
Polycrystal r=0.1 Large r-values for
{210}<-120>
R-values
0.0
0.2
0.4
0.6
0.8
1.0
1.2
g1 g2 g3 g4 g5 g6 g7 g8 g9 g10 g12 g13 g14 g15 P1 P2 P3
Specimen
R
t
wR
Effect of AnnealingEffect of Annealing
0
50
1 00
1 50
2 00
2 50
0 0 .2 0 .4 0 .6 0 .8 1
strain
tru
est
ress
[MP
a]
(1),<100> ,1000C
(2),<111> , 1000C
(3),<110> ,1000C
(4),<211> , 700C
(5),<100> , 700C
0
40
80
1 20
0 0 .0 1 0 .0 2 0 .0 3 0 .0 4 0 .05
strain
tru
es
tre
ss
[MP
a]
(1)
(1)
(2)
(2)
(3)
(3)
(4)
(5)
(4)
(5)
•Yield stress and yield drop increase with annealing temperature
Sample prep for multiaxial tests
Sample prep for multiaxial tests
Multi-axial TestingMulti-axial Testing
A - Uniaxial TestA - Uniaxial Test
B - Uniaxial Test, 90 deg rotated
B - Uniaxial Test, 90 deg rotated
C - Balanced Biaxial TestC - Balanced Biaxial Test
D - Plane StrainD - Plane Strain
localization
E - Plane Strain, 90 deg. rotated
E - Plane Strain, 90 deg. rotated
E – Plane StrainE – Plane Strain
EBSD: Misorientations at the tri-junction
EBSD: Misorientations at the tri-junction
•Slip lines and small-angle grain boundaries
•Diffuse slip, most likely from rapidly changing strain gradients leading to succession of activation/deactivation of localized slip systems
Analysis of present dataAnalysis of present data
What is known ….
Full strain rate tensor at every point on the sample and in time
orientations
What is known ….
Full strain rate tensor at every point on the sample and in time
orientations
What is needed … Slip systems that
are locally active at a given point in time
What is needed … Slip systems that
are locally active at a given point in time
Taylor’s modelTaylor’s model
Imposed strain rate tensor
Write the strain rate tensor as a combination of all the slip systems
Imposed strain rate tensor
Write the strain rate tensor as a combination of all the slip systems
22112313
2322
12
131211
εε- 2
ε
2
ε2
ε ε
2
ε2
ε
2
ε ε
ε
αααα mnnmε α
α
2
γ
ConclusionsConclusions 5 Multi-axial straining tests of tri-
crystal plates with identical orientation performed
Local strain rate data collected Orientation analysis with EBSD
GOAL: determination of locally active slip systems for any given moment
5 Multi-axial straining tests of tri-crystal plates with identical orientation performed
Local strain rate data collected Orientation analysis with EBSD
GOAL: determination of locally active slip systems for any given moment