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