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
Thomas Gnäupel-Herold1,2,Adam Creuziger, T.Foecke3
1University of Maryland2NIST Center for Neutron Research
3NIST Metallurgy Division
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
Tensile TestsOrientations
Tensile Tests
0
50
100
150
200
250
0 0.2 0.4 0.6 0.8 1strain
true
str
ess
[MPa
]
S1S2S3S4S5S6S7S8S9S10S12S13S14S15
1 0 0 1 1 0
1 1 1
S1
S2
S3
S4
S5
S6
S7
S8
S9S10
S12 S13S14
S16
S17
Yield StressYield Stress
0
20
40
60
80
100
120
140
160
g1 g2 g3 g4 g5 g6 g7 g8 g9 g10
g12
g13
g14
g15
P1
P2
P3
Specimen
s0.
2 [M
Pa]
Single crystal
Polycrystal
YS between 25 MPa and 40 MPa
weak anisotropy
25% YS of poly-crystal
R-Values
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 Annealing
0
50
1 00
1 50
2 00
2 50
0 0 .2 0 .4 0 .6 0 .8 1
strain
true
stre
ss[M
Pa]
(1),<100> ,1000C(2),<111> , 1000C(3),<110> ,1000C(4),<211> , 700C(5),<100> , 700C
0
4 0
8 0
1 2 0
0 0 .0 1 0 .02 0 .0 3 0 .04 0 .05
strain
true
stre
ss[M
Pa]
(1)
(1)
(2)
(2)
(3)
(3)
(4)
(5)
(4)
(5)
•Yield stress and yield drop increase with annealing temperature
Sample prep for multiaxial tests
Multi-axial Testing
A - Uniaxial Test
B - Uniaxial Test, 90 deg rotated
C - Balanced Biaxial Test
D - Plane Strain
localization
E - Plane Strain, 90 deg. rotated
E – Plane Strain
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 dataWhat 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
Taylor’s model 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
2γ
Conclusions 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