Department MTM

ICOTOM 17 – 2014 - Dresden

1

Effect of Interstitial Elements & Temperature on Texture

and Substructure evolution of CP Ti during ECAP

Dep. of Materials Engineering, KU Leuven, Belgium

Xiaodong Guo, Marc Seefeldt

Department MTM

Content

2

Backgrounds

Modeling Strategy

Results & Discussions

Conclusion

Department MTM

Origin of this research

3

Nano Titanium Implant®, produced in Timplant, Czech

CP Ti by ECAP can improve biocompatibility, strength, persistency…

Properties depend on: composition, temperature, ECAP die geometry etc.

Department MTM

Aim of this research

4

Our aim is to study the effect of composition, temperature on texture, substructure evolution of CP Ti during the first pass of ECAP

Composition: Interstitial element content, in term of oxygen equivalent content, {O}%Temperature:

Department MTM

Modeling Strategy

5

Deformation Substructure

Prismatic, Basal, Pyramidal

Twins: type of reorientation bands

defect densities

Δε

microscopic mesoscopic

Deformation Texture

VPSC Model

(Simple Shear Mode)

orientations

Δε

Velocity

Gradient

Tensor

Dislocation

Elementary

Processes

macroscopicnanoscopic

)(sCRSS

)(w

Effects on texture through CRSS of slip and twin modes.

Effects on substructure through CRSS of slip and twin modes, stacking fault energy

Department MTM

Slip & Twinning in α-Titanium

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{0001}<11-20> {10-10}<11-20>

{11-22}

{10-11}<11-23> {11-22}<11-23>

Basal Prismatic <a> Pyramidal <a> Pyramidal <c+a> I Pyramidal <c+a> II

Slip Modes

Twinning Modes{11-21}{10-12}

{10-11}<11-20>

Texture simulation: 3 slip modes and 2 twinning modes

Substructure simulation: 3 slip modes

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Effect of Interstitial Elements & Temperature on CRSS

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0.0 0.1 0.2 0.3 0.4 0.5

0

20

40

60

80

100

120

140

160

CR

SS

(MP

a)

O+{N+C}(wt%)

Prismatic

Basal

300 350 400 450 500

0

20

40

60

80

100

120

140

160

CR

SS

(MP

a)

Temperature(oK)

Prismatic

Basal

*Hans Conrad, Progress in Mater. Sci., Vol. 26

CRSS vs Temperature CRSS vs Interstitial Content

CRSS of slip systems increase at lower temperature or with higher interstitial elements content.

CRSS of twinning systems keeps unchanged with temperature and interstitial elements

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CRSS selections

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ECAP

∅ = 𝟗𝟎°,𝜳 = 𝟎°, ∆𝜺 = 𝟏. 𝟏𝟓

Prismatic Basal Pyramidal Ten. Twin Com. Twin

𝟐𝟗𝟖𝑲 120 150 300 120 200

473K 35 60 200 120 200

CRSS with Temperatures

in MPa

Prismatic Basal Pyramidal Ten. Twin Com. Twin

𝑮𝒓𝒂𝒅𝒆 𝟏 75 100 250 150 300

Grade 4 120 150 300 120 200

CRSS with Interstitial contents

in MPa

Department MTM

Texture with two interstitial contents

9

ED

TD

Grade 1

Grade 4

Department MTM

Texture with two temperatures

10

ED

TD

298K, Grade 4

473K, Grade 4

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Effects on prismatic nucleation site density

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0.0 0.2 0.4 0.6 0.8 1.0 1.20

1x1018

2x1018

3x1018

4x1018

Grade 1

Grade 4

Nu

cle

atio

n S

ite

De

nsity (

1/m

-3)

True Strain

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

5.0x1017

1.0x1018

1.5x1018

2.0x1018

2.5x1018

3.0x1018

298K

473K

Nu

cle

atio

n S

ite

De

nsity (

1/m

3)

True Strain

Total Dislocation Density vs Temperature Total Dislocation Density vs Composition

Prismatic nucleation site density decreases at higher temperatures

The value at 373K is lower than that at 473K , it’s due to the relatively higher nucleation site density of basal slip.

So at higher temperature, contribution of basal slip is stronger

Prismatic nucleation site density is only a bit higher with a higher interstitial content

Department MTM

Total Dislocation Density

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Total Dislocation Density vs Temperature Total Dislocation Density vs Composition

Total dislocation density is lower at higher temperature, but due to activation of more basal slip, it’s not a big

difference.

Interstitial element content has a negligible effect on total dislocation density

0.0 0.2 0.4 0.6 0.8 1.0 1.2

1E11

1E12

1E13

1E14

1E15

Grade 1

Grade 4

To

tal D

islo

ca

tio

n D

en

sity(/

m2)

True Strain

0.0 0.2 0.4 0.6 0.8 1.0 1.2

1E12

1E13

1E14

1E15

298K

473K

To

tal D

islo

ca

tio

n D

en

sity(/

m2)

True Strain

Department MTM

Cell & Fragment Size with Interstitial content

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Cell & Frag. Size vs TemperatureCell & Frag. Size vs Interstitial Content

Effect of Interstitial content on the evolution of cell and fragment size is negligible

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

2

4

6

8

10

Cell size of G1

Fragment size of G1

Cell size of G4

Fragment size of G4

Ce

ll &

Fra

gm

en

t siz

e (m

)

True Strain

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

2

4

6

8

10

Cell size 298K

Fragment Size 298K

Cell size 473K

Fragment size 473K

Ce

ll &

Fra

gm

en

t S

ize

(m

)

True Strain

𝑑𝑐 =𝐾𝑐𝜌𝑡𝑜𝑡

𝑑𝑓 ≈𝐾𝑓

𝜃𝑖

* Gunderov et al., MSEA 2013

Department MTM

Validation with Experimental

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Temperature = 473K

0

50

100

150

200

250

300

350

400

0 0.5 1 1.5Equivalent Strain (1)

Equ

iva

len

t S

tre

ss (

MP

a)

A. A. Salem’s curve from simple shear

Simulated for 1 pass of ECAP

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.400

100

200

300

400

500

Simulated

Wolfgang's

Flo

wstr

ess(M

Pa

)

True Strain(1)

Wolfgang’s curve from uniaxial tensile test

Simulated from substructure model

*A. A. Salem, S.R. Kalidindi, R. D. Doherty, Acta, (2003)*Hanka Becker, Wolfgang Pantleon, CMS, 2013

Department MTM 15

Mean Misorientation

0.0 0.2 0.4 0.6 0.8 1.0 1.22.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Mean Misorientation

Me

an

Mis

orie

nta

tio

n(o

)

True Equivalent Strain(1)

Misorientation & Hardening

0

50

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2

True Equivalent Strain (1)

Tru

e Eq

uiv

alen

t S

tres

s (M

Pa)

Simulated

Experimental

- Hardening due to

• Dislocation forest hardening: ∆𝜎𝑓 = 𝑀𝛼𝜌𝐺𝑏 𝜌 𝑡𝑜𝑡

• Long-range stress hardening due to mismatch stresses around FB triple junctions: ∆𝜎𝜔 = 𝑀𝛼𝜃𝐺𝜔

• Texture hardening due to the evolving average Taylor factor 𝑀

10

14

18

Mis

mat

ch S

tres

s (M

pa)

∆𝜎𝜔

Department MTM

Conclusion

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Interstitial element content and temperature has a great effect on

CRSS of slip systems while keeps CRSS of twinning unchanged, thus

has a great on texture evolution.

Evolution of substructure is temperature dependent, but slightly

affected by interstitial element.

Effect of interstitial element will influence the atomistic parameters, but

for the time being, we neglect it.