Review of Results First Wall Helium Management & Refractory Armored Materials L L Snead, T. Hinoki, J. Hunn, C. Blue, N. Hashimoto (ORNL) R. Raffray (UCLA) G. Lucas (UCSB) J. Blanchard (UW) S. Gilliam, B Patnaik, N Parikh (UNC-Chapel Hill) A.Federov (DELFT Netherlands)

 He ion irradiation damage creates vacancies within W that trap He and act as nucleation sites for He bubble growth.  He trapping and bubble growth increases with dose and irradiation temperature due to increasing defect density and thermal mobility.  For low energy, room temp. implantation, growth of He bubbles beneath the surface causes blistering at ~3 x /m 2 and surface exfoliation at ~10 22 /m 2.  These critical doses decrease with temperature and increase with ion energy (interested in ~1-2 MeV He for IFE). Challenge of First Wall Helium Management

Experimental Program (ORNL, UNC, Delft) 1-2 MeV helium implantation ( °C) with intermittent annealing to 2000°C. Effect of microstructure (single-X, CVD and Poly-X tungsten) Exfoliation - TEM, SEM Diffusion - Nuclear Reaction Analysis, Thermal Desorption

 As-implanted produced proton counts  After anneal produced 7900 proton counts As-implanted Annealed Blistered

Before Anneal 2000°C anneal CVD238 counts311 counts Poly X83 counts82 counts Single X582~ 580 counts Effect of Microstructure on Helium Retention (1E19/m2, 50°C implants) Effect of Cyclic Annealing 1E19/m2 in 50 implants 50°C implants, 2000°C anneals in between Single X582 counts272 counts

Effect of Microstructure on Helium Retention at 800°C Single crystal produced no counts Polycrystalline produced 82 counts CVDproduced 238 counts

Observed Area Single Crystal Tungsten 50 x Cyclic RT Implantation/2000°C Anneal Specimen 1m1m Over Focus Image 100nm Under Focus Image 100nm

Under Focus Image 100nm Larger, resolvable bubbles several nanometers 50 x Cyclic RT Implantation/2000°C Anneal

Summary and Plans for Conclusion of He/W Studies Implantation temperature and microstructure have great influence on the diffusion and trapping of helium in tungsten. Single crystal (free of grain boundaries, very low impurity) has significantly less retention of materials studied and essentially no retention at IFE relevant temperatures. Helium bubbles formed in single crystal following very high temperature annealing are several nanometers in diameter indicating very short diffusion lengths possible confounding “engineered porosity” approach to helium management Summary

Complete series of high-temperature implantations and associated TEM to determine controlling microstructural feature. Are grain boundaries or impurities controlling trapping? Complete thermal desorption studies. Determine diffusion coefficient of He in W for transport modeling… Automate and carry out IFE relevant dose/anneal study on candidate tungsten material. Which material? Chopping? Perform degraded energy implantation of He/H. Simulating actual spectrum calculated described by Lucas… Results presented/published in MRS winter meeting and ICFRM-11 Concluding Studies

Refractory Armored Silicon Carbide Raffray data Motivation for this work was to demonstrate at proof-of- principal refractory armored SiC with strong interfacial bonding

Properties of the Plasma Radiant Source Maximum lamp power: 35 MW/m 2 Non-contact heating Rapid heating and cooling Concentration of heating on surface Environment: argon, vacuum, air Three separate plasma heads: 10, 20 and 35 cm arcs Power delivery: flash mode or scan mode as wide as 35 cm, presently Lamp power: form 2% to 100% of available radiant output Change of power levels: less than 20 ms Wavelength of radiant output: µm Wavelength: constant and independent of power level and anode/cathode wear

Coating Optimization (Details in Poster Session) SiC (Hexoloy SA) Pretreatment* Brush or spray powder (W or Mo) IR processing SiC *Pretreatment: Ti vapor deposition W or Mo vapor deposition Anneal 72 hours (1300 or 1500ºC) Vapor deposited Ti Vapor deposited W or Mo Anneal Plasma Arc Lamp Specimen size: 25×15×3 (mm) IR processing: uniform irradiance or scan Flash or scan W or Mo powder

Effect of Scan Speed on Coating Microstructure Melted W Non-melted W Scan speed: 11.0 mm/sec 5mm IRHW31 Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m 2 Cross sectional SEM image in middle region SiC W coating

Effect of Scan Speed on Coating Microstructure Melted W Non-melted W Scan speed: 10.5 mm/sec 5mm IRHW32 Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m 2 SiC W coating Cross sectional SEM image in middle region

Effect of Scan Speed on Coating Microstructure Melted W 5mm IRHW30 Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m 2 Scan speed: 10 mm/sec SiC W coating Cross sectional SEM image in middle region

SEM Images of W Coating Processed at 23.5 MW/m 2 Lamp power: 2350 W/cm 2, 10 mm/sec scan No thick reaction interlayer WC grains adjacent to interface Strong interface Back scattering SEM images W coating SiC W+C

Effect of Processing Condition on Flexural Strength of W Coated SiC W coating side Four point flexural test Specimen size: 50x4x3 mm Support span: 40 mm Loading span: 20 mm Crosshead speed: 10um/sec Substrate strength  W coating was not peeled off during flexural test  Strength of substrate SiC was decreased by IR processing  Vapor deposition prior to powder coating prevented degradation of strength slightly

Thermal Fatigue Experiment Using IR Processing Facility thermomechanical and microstructural stability of interface Rep rate: 10Hz Max. flux: 23.5MW/m 2 (10ms) Min. flux: 5.9MW/m 2 (90ms) Substrate temp. (bottom): 600 ºC Substrate material: silicon carbide Coating material: tungsten (50µm-thick) Specimen size: 50 x 4 x 3 (mm) W coated specimen Cooling table W+C

Thermal Fatigue Experiment Using IR Processing Facility thermomechanical and microstructural stability of interface Rep rate: 10Hz Max. flux: 23.5MW/m 2 (10ms) Min. flux: 5.9MW/m 2 (90ms) Substrate temp. (bottom): 600 ºC Substrate material: silicon carbide Coating material: tungsten (50µm-thick) Specimen size: 50 x 4 x 3 (mm) W coated specimen Cooling table

Thermal Fatigue Experiment Using IR Processing Facility thermomechanical and microstructural stability of interface Rep rate: 10Hz Max. flux: 23.5MW/m 2 (10ms) Min. flux: 5.9MW/m 2 (90ms) Substrate temp. (bottom): 600 ºC Substrate material: silicon carbide Coating material: tungsten (50µm-thick) Specimen size: 50 x 4 x 3 (mm) W coated specimen Cooling table

Effect of Thermal Fatigue on Tungsten Coating Before experiment After 1000 cycles Tungsten coating was not peeled off following 1000 cycle thermal fatigue experiments Rep rate: 10Hz Max. flux: 23.5MW/m 2 (10ms) Min. flux: 5.9MW/m 2 (90ms) Cycle: 1000 Substrate temp. (bottom): 600 ºC

Mapping “over-cooked” Coating (Higher Power, Slower Scan) SiC W coating W C Si Back scattering electron image EDS mapping of W, C, Si  W+C W+Si Hexoloy SiC + W (no pretreatment) Lamp power: 2350 W/cm 2 Scan speed: 9mm/sec 10µm

Summary and Plans for Conclusion of RAC’s Summary A fully dense, high-strength tungsten coating has been applied to SiC. Preliminary thermal fatigue testing shows promise. Concluding Studies What’s required to conclude proof-of-principal? - complete analysis of thermal stability/thermal fatigue of interface - improve uniformity - application to SiC/SiC - results to be published at ICFRM-11

Example from this Conference : N Abe (EPVD) Good microstructure, though low interfacial strength