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