uniaxial and multiaxial plastic deformation of large niobium grains
DESCRIPTION
Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains. Thomas Gnäupel-Herold 1,2 , Adam Creuziger, T.Foecke 3 1 University of Maryland 2 NIST Center for Neutron Research 3 NIST Metallurgy Division. Formability: strain localization on grain boundaries. - PowerPoint PPT PresentationTRANSCRIPT
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