Micro-engineered Armor:Helium Transport
Shahram Sharafat, Q. Hu, M. Andersen, N. GhoniemMechanical Engineering Department, University of California Los Angeles
Lance SneadOak Ridge National Laboratories
High Average Power Laser MeetingGeorgia Institute of Technology
Atlanta, GAFeb. 5-6, 2004
University of California Los Angeles
Outline
• The Battle at “FW”– Battlefield Tour
• The HEROS Code:– Single shot results (10 m and 2 m W)– Multi-shot results (10 m to 0.5m W)
• Future Work:– Bubble kinetics with ORNL, UWM data
• Tungsten-Foam Deformation
He-Implantation and Self-Damage
Processes:• He implantation rates are enormous:
Per shot: ~1.2 He (appm)Damage: ~4.3x10-4 dpa/shotHe/dpa: ~2725 appm/dpa
• In W a 3.6 MeV He can produce: ~308 Vacancies and Self-InterstitialsVacancy- 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
The HEROS Code
HEROS:
Helium Transport, Bubble, & MicROStructural Evolution
• HEROS is a first of its kind helium-behavior modeling code that combines transport and microstructural evolution with spatial dependency
HEROS Code Description
• Fundamental processes are represented by kinetic rate equations (kRT). Rate constants are determined using experimental activation energies.
• Example for Single VACANCIES:
1 2
*2 2
(1 ) ( ) { ( 2 )
( 2 2 3 )}
vv gv i i CIC CIC
vg s gv gv g v
dCfG e C C C x C
dt
C C C C C C C
creation interstitial-vacancy recombination sink absorptionsimilar to Brailsford, Bullough (1972)
• 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:
( , )( ( ) ) ( , ) ( , )v vdC x t CD x Creation x t Loss x t
dt x x
Diffusion Classical kRT
• 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-clustersGlissile SIA-clustersSessile dislocation loopsMatrix Helium BubblesPrecipitate BubblesGrain-Boundary Bubbles
• Results using 200 bins for 10, 5, 2, 1, and 0.5 m ligaments are presented
• Bubble kinetics will be added to HEROS (data from ORNL, UWM)
*S. Sharafat, N. M. Ghoniem, J. Nucl. Mater., 283-287 (2000) 789-793.
HEROS Code Description (cont.)
Implantation Profile
• Spatial- and temporal ion implantation- and damage profiles are estimated using SRIM2003 and are based on the Threat Spectra
1.E+15
1.E+16
1.E+17
1.E+18
1.E+19
1.E+20
1.E+01 1.E+02 1.E+03 1.E+04
Energy (eV)
Hel
ium
(#/
sho
t)
He4 - Debris
He4 - Burn
Based on Threat Spectra
5 um
5 um
5 um
200keV
700keV
2MeV
Helium Implantation& Self Damage Distribution (%)
5m 7m x0
77
100
1
0 5m 10m
Ligament Width
He
HEROS Code Operation1. Helium implantation and Self-Damage
rates are ramped up from 0 to max at 1.9x10-6s (based on Threat Spectra).
2. Along with the implantation profile the temperature is ramped up from an operating temperature (<800C) to a max. temperature (>2700C).
3. Both helium implantation and self damage are turned off at 1.9x10-6s(tungsten is now at its maximum temperature ~2700 C).
4. The W temperature is ramped down back to the operating temperature by 10-3s.
5. 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.
6. Repeat 5 through 6
Comparison of 1D (Solid Lines) and 3D (Dashed Lines) Transient Analysis:
0
500
1000
1500
2000
2500
3000
1.00E-10 1.00E-08 1.00E-06 1.00E-04 1.00E-02 1.00E+00
Time (s)
Te
mp
era
ture
( C
)
WSurface
steelsur
steelcoolant
3D-W-surf
3D-W-ODS
3D-SteelCoolant
HEROS Temperature Profile (red)
Single Shot Results: 10-m Ligament
Single Vacancies Self-Interstitials
Red Timer: Implantation & Self-Damage is onGreen Timer: Implantation & Self-Damage is OFF
0 5m 10m
ligamentHe
Single Shot Results: 10-m Ligament
Matrix He-Bubbles
Red Timer: Implantation & Self-Damage is onGreen Timer: Implantation & Self-Damage is OFF
0 5m 10m
ligamentHe
Single Shot Results: 2-m Ligament
Int.- Helium
Vacancies
Red Timer: Implantation & Self-Damage is onGreen Timer: Implantation & Self-Damage is OFF
Matrix He-Bubbles:
0 1m 2m
ligamentHe0 1m 2m
ligament
Matrix Bubble Density
1
Bbl Bbl
mfpN D
Bubble Mean Free Pathlength
Matrix Bubble He-Content
Bubble Radius
(cm)
SEM image (High temp./Low fluence)
~2600℃ 、 1.7x 1022 He/m2
3.5s/30s( 8S)18.7 keV, 6.7x 1020 He/m2sWF-6(20x20x0.1mm)
20mm
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.
2μm
Slide from: K. Tokunagaa
ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan
For HAPL: R=6.5m Chamber: ~8x1022 He/m2/day
18.7 keV He Ion Distribution
SRIM2003
Experiments Self Damage:18.7 keV ~ 5 Vacancies/He
~ 0.5m Range
IFE Self Damage:3.6 MeV ~ 300 Vacancies/He ~ 4-5m Range
SEM image (High temp./High fluence)
~ 2600℃ 、3.3x 1023 He/m2
3.5s/30s( 145S)18.7 keV, 6.7x 1020 He/m2sWF-2(20x20x0.1mm)
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.
2μm
1μm
Slide from: K. Tokunagaa
ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan
For HAPL: 3.3x1023
He/m2 in ~4.5 day
SEM image of cross section
~2600℃ 、 3.3x 1023 He/m2
3.5s/30s( 145S), 18.7 keV, 6.7x 1020 He/m2s, WF-2(20x20x0.1mm)
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 50 -500 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.
Surface
20μm 1μm
K. Tokunagaa
ICFRM-11 Dec. 7-12, 2003 Kyoto Japan
Deformation and Heating of Tungsten Foam
Deformation of W-Foam
Deformation of Solid Foam
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.
Conclusions and Future Work• Conclusions:
─ 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
Backup Slides
Average Matrix Bubble Density
He-Implantation and Self-Damage
Processes:• He Implantation rates are enormous:
Per shot: ~1.2 He (appm)Damage: ~4.3x10-4 dpa/shotHe/dpa: ~2725 appm/dpa
• He Self-Damage in W (He@ 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
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/m2sWB-9(10x10x1mm)
1900℃ 、 2.5x 1022 He/m2
3.5s/30s( 8S)18.7 keV, 1.0 x 1021 He/m2sWC-6(10x10x1mm)
Blisters with a diameter of 0.5 -1.0 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.
2μm 2μm
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/m2sWB-7(10x10x1mm)
1400℃ 、 5.0x 1023 He/m2
3.5s/30s( 145S)14 keV, 1.0x 1021 He/m2sWB-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)
2μm 2μm
He/Damage Rates in Tungsten
20
2
6 3
3 16 3
6
1 1.96 10 (~ 3 )
531 (6.5 )
5 10 ; 2655
/ 7.46 10 /
/ 1.17 10 /
/ 308 ; / 60
.368
He
He
Shot He MeV
Area m mChamber
PenetrationDepth m Volume cm
C shot cm He shot cm
C W at at at shot
Vacancies He Vacancies H
displ per atom
shot
6 4
6 6
3
3
1.17 10 4.3 10 /
1.9 10 5.85 10 /
/
2.72 /
226 / 2.15 10
/ 2725 / 10
: :o
He
He
o
dpa
o
dpa shot
On Time s G He at
dpa s
app pa
s
m d
G
G
dpa rate dpa s
He dpa appm dpa
Pulsed Steady State
Pulsed Damage and He-Implantation Rates are Enormous:
Steady-State: Implantation
1.E-23
1.E-18
1.E-13
1.E-08
1.E-03
1.E+02
1.E+07
1.E+12
1.E+17
1.E+22
1.E+27
1.E-15 1.E-12 1.E-09 1.E-06 1.E-03 1.E+00 1.E+03 1.E+06
TIME (s)
NU
MB
ER
/ c
m3
CV
CI
CHe
CHeV
C2HeV
C2He
CB-Nucl
C_BB
He_in_BB
He@PPT
He@GB
N_CVC
CIC
C2I
CI_Loop
T=650oC
Disl. Density = 109/cm2 Grain size = 30 um Precipitates = 109/cm3 Gdpa = 2.15e-3 dpa/sGHE = 5.85e-6 He/at-s
Gradual and steady increase in Bubble Conc.
Bubbles
Vac.
Int.
1-He
He @ GB
He in BB
Implantation
1500oC
At 1500oC almost no Bubbles SurvivePulsed He/Damage with Temperature Spike:
1.E-23
1.E-19
1.E-15
1.E-11
1.E-07
1.E-03
1.E+01
1.E+05
1.E+09
1.E+13
1.E+17
1.E+21
1.E-15 1.E-13 1.E-11 1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01
TIME (s)
NU
MB
ER
/ c
m3
CV
CI
CHe
CHeV
C_BB
He@GB
5 0 0
1 0 0 0
1 5 0 0
2 0 0 0
2 5 0 0
3 0 0 0
3 5 0 0
TE
MP
. (K
)
T e m p
T-Spike
“Trapped” Helium
HeV
Bubbles
Grain Size ~ Ligament Radius~ 10 um
0m 20m
Evac1.5
EHe0.2
5m
Emeff
00He x
C
0He x lC
0, exp
,
effm
B
E xD x t D
k T x t
x
Spatial Diffusion Model for Helium Release
Key Defect Parameters