Microengineered Armor:

1
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
• 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 is a first of its kind helium-behavior
  modeling code that combines transport and
  microstructural evolution with spatial dependency

• Fundamental processes are represented by kinetic
  rate equations (kRT). Rate constants are
  determined using experimental activation
  energies.

• Example for Single VACANCIES

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., 283-287
  (2000) 789-793.

7
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

2MeV
700keV
200keV
Ligament Width
5 um
He
5 um
5 um
0 5mm 10mm
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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 (lt800C) to a max. temperature
  (gt2700C).
• 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)
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Single Shot Results 10-mm Ligament
Single Vacancies
Self-Interstitials
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
0 5mm
10mm
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
He
0 1mm 2mm
ligament
0 1mm
2mm
Int.- Helium
Red Timer Implantation Self-Damage is
on Green Timer Implantation Self-Damage is OFF
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Matrix Bubble Density
13
Bubble Mean Free Pathlength
14
Matrix Bubble He-Content
15
Bubble Radius
(cm)
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SEM image (High temp./Low fluence)
2µm
20mm
Slide from K. Tokunagaa ICFRM-11, Dec. 7-12,
2003, Kyoto, Japan For HAPL R6.5m 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.

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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
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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
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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 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.

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 (ltfew 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.

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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

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Backup Slides
26
Average Matrix Bubble Density
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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 (He_at_ 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

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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 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.

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SEM image of surface (High fluence)
2µm
2µm
800??3.3 x 1023 He/m2 3.73.9s/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)

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He/Damage Rates in Tungsten

Pulsed Damage and He-Implantation Rates are
Enormous
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Steady-State
Gradual and steady increase in Bubble Conc.
Bubbles
He _at_ GB
Vac.
1-He
Int.
He in BB
T650oC
Disl. Density 109/cm2 Grain size 30 um
Precipitates 109/cm3 Gdpa 2.15e-3
dpa/s GHE 5.85e-6 He/at-s
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Pulsed He/Damage with Temperature Spike
At 1500oC almost no Bubbles Survive
Bubbles
HeV
Trapped Helium
T-Spike
Grain Size Ligament Radius 10 um
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Spatial Diffusion Model for Helium Release
Evac?1.5
Emeff
EHe?0.2
20?m
5?m
0?m
x
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Key Defect Parameters