Presentation at icotom17 dresden 20140826
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Transcript of Presentation at icotom17 dresden 20140826
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
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
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
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
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
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
Department MTM
Effects on prismatic nucleation site density
11
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
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
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
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
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
14
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
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.