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Micro-engineered Armor: Helium Transport Shahram Sharafat, Q. Hu, M. Andersen, N. Ghoniem

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

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Micro-engineered Armor: Helium Transport Shahram Sharafat, Q. Hu, M. Andersen, N. Ghoniem

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  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. The Battle at “FW” Battlefield Tour The HEROSCode: 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 Outline

  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. creation interstitial-vacancy recombination similar to Brailsford, Bullough (1972) sink absorption Classical kRT Diffusion 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 experimentalactivation energies. • Example for Single VACANCIES: • 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:

  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. Helium Implantation& Self Damage Distribution (%) 100 77 1 0 5m 7m x 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 0 5mm 10mm 5 um

  8. 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. He ligament 0 5mm 10mm 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 0 1mm 2mm He ligament 0 1mm 2mm 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) 2μm 20mm Slide from: K. Tokunagaa ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan For HAPL: R=6.5m Chamber: ~8x1022He/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 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 (<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 • 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

  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 • HeSelf-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

  28. 2μm 2μm 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.

  29. SEM image of surface (High fluence) 2μm 2μm 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. Implantation Steady-State: Gradual and steady increase in Bubble Conc. Bubbles He @ GB Vac. 1-He Int. He in BB T=650oC Disl. Density = 109/cm2 Grain size = 30 um Precipitates = 109/cm3 Gdpa = 2.15e-3 dpa/s GHE = 5.85e-6 He/at-s

  32. Implantation 1500oC Pulsed He/Damage with Temperature Spike: At 1500oC almost no Bubbles Survive 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 5m 20m 0m x

  34. Key Defect Parameters

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