1. Micro-engineered Armor:
University of California Los Angeles
Micro-engineered Armor:
Helium Transport
Shahram Sharafat, Q. Hu, M. Andersen, N. Ghoniem
Mechanical Engineering Department, University of California Los Angeles
Lance Snead
Oak Ridge National Laboratories
High Average Power Laser Meeting
Georgia Institute of Technology
Atlanta, GA
Feb. 5-6, 2004

2. Outline The Battle at “FW” The HEROS Code: Future Work:
Battlefield Tour
The HEROS Code:
Single shot results (10 mm and 2 mm W)
Multi-shot results (10 mm to 0.5mm W)
Future Work:
Bubble kinetics with ORNL, UWM data
Tungsten-Foam Deformation

3. He-Implantation and Self-Damage
Processes:
He implantation rates are enormous:
Per shot: ~1.2 He (appm)
Damage: ~4.3x10-4 dpa/shot
He/dpa: ~2725 appm/dpa
In W a 3.6 MeV He can produce:
~308 Vacancies and Self-Interstitials
Vacancy- and Self-Interstitial clusters
Microstructural Features:
Simple defects (V, SIA, He, HemVn),
Immobile V-clusters
Glissile SIA-clusters
Sessile dislocation loops
Matrix Helium Bubbles
Precipitate Bubbles
Grain-Boundary Bubbles

4. The HEROS Code
HEROS:
Helium Transport, Bubble, & MicROStructural Evolution

5. HEROS Code Description
HEROS augments the kRT with diffusion terms discretized in space for three species: V, SIA, and interstitial-He. All diffusion rates are based on experimental activation energies:
HEROS is a first of its kind helium-behavior modeling code that combines transport and microstructural evolution with spatial dependency
Example for Single VACANCIES:
Fundamental processes are represented by kinetic rate equations (kRT). Rate constants are determined using experimental activation energies.
creation
interstitial-vacancy recombination
sink absorption
similar to Brailsford,
Bullough (1972)
Diffusion
Classical kRT

6. HEROS Code Description (cont.)
HEROS’ core kRT is based on previously developed models that showed good agreement with experimental bubble concentrations in Vanadium*.
The following species were tracked up to 200 shots:
Simple defects (V, SIA, He, HemVn),
Immobile V-clusters
Glissile SIA-clusters
Sessile dislocation loops
Matrix Helium Bubbles
Precipitate Bubbles
Grain-Boundary Bubbles
Results using 200 bins for 10, 5, 2, 1, and 0.5 mm ligaments are presented
Bubble kinetics will be added to HEROS (data from ORNL, UWM)
*S. Sharafat, N. M. Ghoniem, J. Nucl. Mater., (2000)

7. Helium Implantation& Self Damage Distribution (%)
Based on Threat Spectra
Implantation Profile
Spatial- and temporal ion implantation- and damage profiles are estimated using SRIM2003 and are based on the Threat Spectra
Helium Implantation& Self Damage Distribution (%)
5m
7m x 77
100 1
2MeV
700keV
200keV
Ligament Width He
5 um
5 um
mm mm
5 um

8. HEROS Temperature Profile (red)
HEROS Code Operation
Helium implantation and Self-Damage rates are ramped up from 0 to max at 1.9x10-6s (based on Threat Spectra).
Along with the implantation profile the temperature is ramped up from an operating temperature (<800C) to a max. temperature (>2700C).
Both helium implantation and self damage are turned off at 1.9x10-6s (tungsten is now at its maximum temperature ~2700 C).
The W temperature is ramped down back to the operating temperature by 10-3s.
The code continues up to 0.2 s, when the next shot starts:
Defect profiles of the previous shot are used as the starting conditions the next shot.
Repeat 5 through 6
HEROS Temperature Profile (red)

9. Single Shot Results: 10-mm Ligament
Single Vacancies
Self-Interstitials
mm mm
ligament He
Red Timer: Implantation & Self-Damage is on
Green Timer: Implantation & Self-Damage is OFF

10. Single Shot Results: 10-mm Ligament
Matrix
He-Bubbles He
ligament
mm mm
Red Timer: Implantation & Self-Damage is on
Green Timer: Implantation & Self-Damage is OFF

11. Single Shot Results: 2-mm Ligament
Vacancies
Matrix He-Bubbles:
ligament
mm mm He
ligament
mm mm
Int.- Helium
Red Timer: Implantation & Self-Damage is on
Green Timer: Implantation & Self-Damage is OFF

12. Matrix Bubble Density

13. Bubble Mean Free Pathlength

14. Matrix Bubble He-Content

15. Bubble Radius
(cm)

16. SEM image (High temp./Low fluence)
20mm
Slide from: K. Tokunagaa
ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan
For HAPL: R=6.5m Chamber:
~8x1022 He/m2/day
~2600℃、1.7x 1022 He/m2
3.5s/30s( 8S)
18.7 keV, 6.7x 1020 He/m2s
WF-6(20x20x0.1mm)
The color of surface becomes to be white from metallic sliver color by the irradiation up to ～1022 He/m2.
Fine uneven morphology and small holes are observed on the surface.

17. 18.7 keV He Ion Distribution
Experiments Self Damage:
18.7 keV ~ 5 Vacancies/He
~ 0.5mm Range
IFE Self Damage:
3.6 MeV ~ 300 Vacancies/He
~ 4-5mm Range
SRIM2003

18. SEM image (High temp./High fluence)
～2600℃、
3.3x 1023 He/m2
3.5s/30s( 145S)
18.7 keV, 6.7x 1020 He/m2s
WF-2(20x20x0.1mm)
Slide from: K. Tokunagaa
ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan
For HAPL: 3.3x1023 He/m2 in ~4.5 day
2μm
20mm
When fluence is beyond ～1023 He/m2, the color of surface becomes to be black
The surface is modified resulting in a fine uneven morphology and holes with a diameter of about 50 nm are observed on the surface.
1μm

19. SEM image of cross section
Surface
20μm
1μm
~2600℃、3.3x 1023 He/m2
3.5s/30s( 145S), 18.7 keV, 6.7x 1020 He/m2s, WF-2(20x20x0.1mm)
K. Tokunagaa
ICFRM-11
Dec. 7-12, 2003
Kyoto Japan
Grain growth by re-crystallization occurs.
Many horn-like protuberances with a width of about 300 nm and a length of about 1 μm are observed at the surface. In addition, He bubbles with a diameter of about nm are observed near surface.
The surface modification is considered to be formed by the He bubbles and their coalescence, the migration of He bubbles near surface.

20. Deformation and Heating of Tungsten Foam

21. Deformation of W-Foam

22. Deformation of Solid Foam

23. Work in Progress
Bubble Kinetics affects bubble evolution, particularly for “high” temperature spikes.
The small (<few nm) “finely” dispersed bubbles contain small amounts of Helium and are thus likely to diffuse readily under high temperature gradients.
Bubble kinetics modeling will be based on bubble/pore migration in nuclear oxide fuels:
Bubbles/pores migrate up the temperature gradient.
Bubble migration is also affected by stress.

24. Conclusions and Future Work
A new specialized Helium Transport Code (HEROS) has been developed for the first time for IFE conditions.
Single Helium transport is extremely fast.
This leads to a competition between self-trapping in clusters and migration to open surfaces.
The mean-free-path for nucleation is significantly smaller than current ligament sizes.
HEROS can be used to map out an optimization path for micro-engineered FWs
Future efforts:
Fully-coupled heat transfer and helium transport
Temperature gradient driven bubble kinetics
Optimization of armor feature geometry and dimensions.
Determination of stress evolution in optimized foam
Influence of stress gradients on bubble transport
Explore process modifications for high Helium recycling FWs

25. Backup Slides

26. Average Matrix Bubble Density

27. He-Implantation and Self-Damage
Processes:
He Implantation rates are enormous:
Per shot: ~1.2 He (appm)
Damage: ~4.3x10-4 dpa/shot
He/dpa: ~2725 appm/dpa
He Self-Damage in W 3.6 MeV):
About 308 Single Vacancies and Self-Interstitial Atoms (SIA)
Plus Clusters of Vacancy and SIA Clusters
Microstructural Features:
Simple defects (V, SIA, He, HemVn),
Immobile V-clusters
Glissile SIA-clusters
Sessile dislocation loops
Matrix Helium Bubbles
Precipitate Bubbles
Grain-Boundary Bubbles

28. SEM image of surface (low fluence)
800℃、1.7 x 1022 He/m2
3.9s/30s( 7S)
18.7 keV, 6.7 x 1020 He/m2s
WB-9(10x10x1mm)
1900℃、2.5x 1022 He/m2
3.5s/30s( 8S)
18.7 keV, 1.0 x 1021 He/m2s
WC-6(10x10x1mm)
Blisters with a diameter of μm are formed and exfoliation of blister skin is partially observed at a peak temp. of 800 ℃. However, surface modification is relatively small at a high peak temperature of 1900 ℃.
The reason why blister is not formed at a high temperature is considered be the lack of pressure in the bubbles due to the coalescence of vacancies and helium bubbles, and the broad depth distribution of the bubbles by migration.

29. SEM image of surface (High fluence)
800℃、3.3 x 1023 He/m2
3.7～3.9s/30s(128S)
18.7 keV, 6.7x 1020 He/m2s
WB-7(10x10x1mm)
1400℃、5.0x 1023 He/m2
3.5s/30s( 145S)
14 keV, 1.0x 1021 He/m2s
WB-4(10x10x1mm)
Holes with a diameter of 1.5μm are observed. In addition, fine modification on the bottom of the holes are also observed.
(800℃、3.3 x 1023 He/m2 )
Surface is finely modified into wavy structure. This is considered to be the result of erosion due to sputtering caused by He irradiation.
(1400℃、5.0x 1023 He/m2)

30. He/Damage Rates in Tungsten
Pulsed Damage and He-Implantation Rates are Enormous:

31. Steady-State: Gradual and steady increase in Bubble Conc. Implantation
Bubbles GB
Vac.
1-He
Int.
He in BB
T=650oC
Disl. Density = 109/cm2 Grain size = 30 um
Precipitates = 109/cm Gdpa = 2.15e-3 dpa/s
GHE = 5.85e-6 He/at-s

32. Pulsed He/Damage with Temperature Spike:
At 1500oC almost no Bubbles Survive
Implantation
1500oC
Bubbles
HeV
“Trapped”
Helium
T-Spike
Grain Size ~ Ligament Radius~ 10 um

33. Spatial Diffusion Model for Helium Release
Evac1.5
Emeff
EHe0.2
0m
5m
20m x

34. Key Defect Parameters