An Advanced Perspective on Twin Growth and Slip in NiTihtml.mechse.illinois.edu/.../2014/08/ICOMAT-presentation-2014.ppt_.pdf · An Advanced Perspective on Twin Growth and Slip in

University of Illinois at Urbana Champaign

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An Advanced Perspective on Twin Growth and Slip in NiTi

Huseyin Sehitoglu, Tawhid Ezaz, H.J.Maier

Department of Mechanical Science & Engineering University of Illinois, Urbana

University of Paderborn, Germany ICOMAT-2011, September 6, 2011

Funded by NSF- Division of Materials Research

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Presentation Outline •  Detwinning mechanism of Type II-1 twin in

Martensitic NiTi •  Compound twinning in Martensite (001),

(100) and Modes •  Twinning in Austenite (112) and (114)

Modes •  Slip in B2 NiTi

(201)


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Fault Energy Measurement: Example with FCC

2( )mJm

γ

2116

xua ⎡ ⎤⎣ ⎦

Perfect fcc Unstable Stable stacking fault

is linked to Dislocation Nucleation

GSFE GPFE

2116

xua ⎡ ⎤⎣ ⎦

is the energy barrier to overcome during Twin Nucleation

usγ

isfγ

UTγ

2layertwinγ

TMγ

usγ

is the barrier to overcome during Twin growth

TMγ

Unstable Twin fault 2 layer twin

UTγ

FCC is the Simplest!

A B C

A

A B C

B C A B C A

A B C

A

A B C

B C A B C A

B C

B

A B A

C A B C A B

b b/2 1.5b 2b

[111]

[211]


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Detwinning and Twinning of NiTi Martensite

Adapted from Ishida et al.,2006


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Type II-1 twins

Liu, Van Humbeeck, 46, 1998, Acta Mat. Xie,Liu,84,3497,2004, Acta Mat.

Phenomenological Theory provides twinning plane to be irrational (0.7205 1 1)

Experimentally evidence of rational

ledges and steps

(1 1 1)


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Fault Energy in Type II twin

Ezaz -Sehitoglu., APL, 2011

TMth b

γτ π=


•  Detwinning mechanism of Type II-1 twin in Martensitic NiTi

•  Compound twinning in Martensite (001), (100) and

•  Twinning in Austenite, (112) and (114)

(201)

Outline

•  VASP-PAW-GGA

•  9x9x9 k-point mesh with 273.2 eV energy cutoff.

• Convergence assessed with increasing L


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(001) Compound Twin

(001) Twin boundary

(001) Twin boundary

Twin formation due to glide of twinning partial a/2 [100]


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(001) Compound Twin-GSFE and GPFE

2TM = 7.6mJ /mγ

2UT = 24mJ / mγ

2

mJ

m! " #$ %& '

Generalized planar fault energy (GPFE)

xua

2

mJ

m! " #$ %& '

Generalized stacking fault energy (GSFE)

220 /us mJ mγ =

xua 2.884a A= & a aa[100] = [100]+ [100]

2 2Ezaz, Sehitoglu, Acta. Mat, 2011


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2

mJm

γ ⎛ ⎞⎜ ⎟⎝ ⎠

xuc

4.66= &c A

(100) Compound Twin

Onda et al., 33,354,1992, JIM, Mats. Trans.

[ ]100

[ ]001

[ ]010 Ti Ni

Generalized stacking fault energy (GSFE)

No Metastable Position,

Barrier too high


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Energy Barrier of (100) Twin

2

mJm

γ ⎛ ⎞⎜ ⎟⎝ ⎠

xuc

241TMEmJm

γ =

[ ]00113.5

=M

cc

Generalized planar fault energy (GPFE) [ ]100

[ ]001

[ ]010

Ti Ni 0.46 A Shuffle in Ti

0.23 A Shuffle in Ni

3. [001]9a

B19’ 3 layer twin aMer only shear 3 layer twin aMer shuffle

following shear

Shear Direction


Two different Twin growth mechanism

Ledge Ledge

Matrix

Twin

Matrix

[100] [100] [100]2 2a aa → +

[100]

(001]

Displacement

Faul

t Ene

rgy

Shear

Shuffle

[001]

(100]

Aided by twinning partial

No twinning partial, combined shear and shuffle

Displacement

Faul

t Ene

rgy

Without shuffle

With shuffle

Displacement


Compound Twin (201)

(201)

[102]

[201]

Faul

t Ene

rgy

(mJ/

m2 )

| 102 |xu

Generalized Stacking Fault Energy (GSFE)


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Energy Barrier of Twin

Gives the exact coupling of Shear and shuffle

Computationally extensive!

1st Energy Barrier

Metastable position

0,0 0.5,0

1,1

0.5,1

0,1

3 layer twin

4 layer twin

Metastable position

Shear, e

Shu

ffle.h

Faul

t Ene

rgy

(mJ/

m2 )

Reaction path along MEP

1st Energy Barrier

2nd Energy Barrier

2nd Energy Barrier

(201)


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(001), (100), Compound Twins

Twin

Mig

ratio

n E

nerg

y g T

M (m

J/m

2 )

ux/b

(001)[100](100)[001](201)[102]

K1

η1

(τ shear )ideal =

δγδux max

(MPa) { }( )/τ π γ=TMideal TM twinb (MPa)

(001) [100] 277 165

(100) [001] 4530 1790

(201) [102] 107060 3900

Twin growth stress is proportional to the twin migration energy

(201)

Ishida et al., 2005 3 layer Twin

4 layer Twin

5 layer Twin


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Digital Image Correlation Results displaying Multiple Twin Modes During Deformation of Martensite


•  Introduction to NiTi – Applications – Shape Memory Behavior

•  Detwinning mechanism of Type II twin in Martensitic NiTi

•  Compound twinning in Martensite (001), (100) and

•  Twinning in Austenite, (112) and (114)

(201)

Outline


(112) and (114) Twin in Austenite

(112) Twin (114) Twin

(112) And (114) are the mostly observed twin systems

Nishida et al., 2003 18


(112) Pseudotwinning in B2 NiTi 3b 4b

2

mJm

γ ⎛ ⎞⎜ ⎟⎝ ⎠

[ ]1116

xua

Ni – In Plane Ti – In Plane

Ni – Out of Plane Ti – Out of Plane [ ]/ 6 111b a=

Shear Magnitude

Shear Direc0on

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s =

211⎡ ⎤⎣ ⎦

[ ]111

No metastable position, and labeled as ‘impossible’.


Coupled shear and shuffle mechanism during (112) twin growth

[ ]1116ab= 1

2s =

s

4 layer twin 5 layer twin Application of only shear

Ortho

structure

211⎡ ⎤⎣ ⎦

[ ]111


PES and MEP of (112) Twin

4 layer Twin

5 layer Twin

2

mJm

γ ⎛ ⎞⎜ ⎟⎝ ⎠

Reaction coordinate along MEP 4 layer Twin

5 layer Twin

Pseudotwin


(114) Deformation Twin (B2)- The ‘elusive’ one


Different Shuffle Possibilities


PES and MEP in (114) twinning

Normalized displacement / | 221 |xu a

Faul

t Ene

rgy

(mJ/

m2 )

Faul

t Ene

rgy

(mJ/

m2 )

Reaction Coordinate along MEP

• No Energy well at

•  Twinning combines shear and shuffle.

• Barrier energy of 148 mJ/m2

= / 18[221]b a


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!

Sharp Boundaries Further Lower the Energy Barriers


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Presentation Outline •  Detwinning mechanism of Type II-1 twin in

Martensitic NiTi •  Compound twinning in Martensite (001),

(100) and Modes •  Twinning in Austenite (112) and (114)

Modes •  Slip in B2 NiTi

(201)


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Consequence of Slip in Shape Memory


Slip Systems in B2 NiTi

2

mJm

γ ⎛ ⎞⎜ ⎟⎝ ⎠

[100]xu a [111]xu a

(011)[100] (011)[111]

Most observed slip system in B2 NiTi, Chumlyakov, 2004, Norfleet et al., 2010, Delville et al. , 2010

Not presented in early work, lower barrier energy in (1-11) direction


Experimental observation of novel [111](011) system systems

(011)[100] (011)[111]


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Slip

Plane

Slip

Direction max

( )shear idealxu

δγτδ

= (MPa)

(011) [100] 1034

(011) [111] 726

( 211) [111] 7430

(100) [010] 9320

Summary of Slip Systems


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Summary


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Conclusions •  Twinning is favored over slip in the case B19’ martensite

(a key reason why shape memory works). •  Shuffles play a significant role in Type II-1, (100), (201)

twinning in martensite. •  (112) and (114) twinning in B2 NiTi has to overcome

much lower barrier with shear and shuffle with comparable

•  [111](011) slip has been shown to be significant in B2 NiTi along with [100](011) slip both with experiments and simulations.


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Thank You

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An Advanced Perspective on Twin Growth and Slip in NiTihtml.mechse.illinois.edu/.../2014/08/ICOMAT-presentation-2014.ppt_.pdf · An Advanced Perspective on Twin Growth and Slip in