ICOTOM stands for International Conference on Textures of Materials. it is the biggest conference in the field of texture and microstructure of materials in the world.

1. 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

2. Department MTM
Content
2
Backgrounds
Modeling Strategy
Results & Discussions
Conclusion

3. 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.

4. 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:

5. 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
)(s
 CRSS
)(w

 Effects on texture through CRSS of slip and twin modes.
 Effects on substructure through CRSS of slip and twin modes, stacking fault energy

6. Department MTM
Slip & Twinning in α-Titanium
6
{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

7. Department MTM
Effect of Interstitial Elements & Temperature on CRSS
7
0.0 0.1 0.2 0.3 0.4 0.5
0
20
40
60
80
100
120
140
160
CRSS(MPa)
O+{N+C}(wt%)
Prismatic
Basal
300 350 400 450 500
0
20
40
60
80
100
120
140
160
CRSS(MPa)
Temperature(
o
K)
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

8. Department MTM
CRSS selections
8
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

9. Department MTM
Texture with two interstitial contents
9
ED
TD
Grade 1
Grade 4

10. Department MTM
Texture with two temperatures
10
ED
TD
298K, Grade 4
473K, Grade 4

11. Department MTM
Effects on prismatic nucleation site density
11
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0
1x10
18
2x10
18
3x10
18
4x10
18
Grade 1
Grade 4
NucleationSiteDensity(1/m-3)
True Strain
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.0
5.0x10
17
1.0x10
18
1.5x10
18
2.0x10
18
2.5x10
18
3.0x10
18
298K
473K
NucleationSiteDensity(1/m3)
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

12. Department MTM
Total Dislocation Density
12
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
TotalDislocationDensity(/m2)
True Strain
0.0 0.2 0.4 0.6 0.8 1.0 1.2
1E12
1E13
1E14
1E15
298K
473K
TotalDislocationDensity(/m
2
) True Strain

13. Department MTM
Cell & Fragment Size with Interstitial content
13
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
Cell&Fragmentsize(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
Cell&FragmentSize(m)
True Strain
𝑑 𝑐 =
𝐾𝑐
𝜌𝑡𝑜𝑡
𝑑 𝑓 ≈
𝐾𝑓
𝜃𝑖
* Gunderov et al., MSEA 2013

14. Department MTM
Validation with Experimental
14
Temperature = 473K
0
50
100
150
200
250
300
350
400
0 0.5 1 1.5
Equivalent Strain (1)
EquivalentStress(MPa)
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 0.40
0
100
200
300
400
500
Simulated
Wolfgang's
Flowstress(MPa)
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

15. Department MTM 15
Mean Misorientation
0.0 0.2 0.4 0.6 0.8 1.0 1.2
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Mean Misorientation
MeanMisorientation(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)
TrueEquivalentStress(MPa)
Simulated
Experimental
- Hardening due to
• Dislocation forest hardening: ∆𝜎𝑓 = 𝑀𝛼 𝜌 𝐺𝑏 𝜌 𝑡𝑜𝑡
• Long-range stress hardening due to mismatch stresses around FB triple junctions: ∆𝜎 𝜔 = 𝑀𝛼 𝜃 𝐺𝜔
• Texture hardening due to the evolving average Taylor factor 𝑀
10
14
18
MismatchStress(Mpa)
∆𝜎 𝜔

16. Department MTM
Conclusion
16
 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.