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)

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Review of ResultsFirst 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 1021/m2

and surface exfoliation at ~1022/m2.

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 (600-800°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

Polycrystalline

Implanted 10 22/m2 at 800 C As-implanted and after anneal

0

200

400

600

800

1000

1200

1400

12500 13000 13500 14000

Energy (keV)

CountsAs-implanted

2000C anneal

As-implanted produced 18000 proton counts After anneal produced 7900 proton counts

As-implanted

Annealed

Blistered

Before Anneal 2000°C annealCVD 238 counts 311 countsPoly X 83 counts 82 countsSingle X 582 ~ 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 X 582 counts 272 counts

Implanted 10 19/m2 at 800 CAs-implanted Analysis

0

5

10

15

20

25

12500 13000 13500 14000

Energy (keV)

Counts

CVD

Polycrystalline

Single Crystal

Effect of Microstructure on Helium Retention at 800°C

Single crystal produced no counts

Polycrystalline produced 82 counts

CVD produced 238 counts

Observed Area

Single Crystal Tungsten50 x Cyclic RT Implantation/2000°C Anneal

Specimen

1mOver 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

500

1000

1500

2000

2500

0 2 4 6 8 10Time ( )s

(100 ) Tungsten micron Armor on SiC

- ( ~ 2800° )Non Armored SiC Sublimes at C

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/m2

•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: 0.2-1.4 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 orscan

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/m2

Cross sectional SEM image in middle region

SiC

W coating


Melted W

Non-melted W

Scan speed: 10.5 mm/sec

5mm

IRHW32


SiC

W coating



Melted W

5mm

IRHW30


Scan speed: 10 mm/sec SiC

W coating


SEM Images of W Coating Processed at 23.5 MW/m2

Lamp power: 2350 W/cm2, 10 mm/sec scan

•No thick reaction interlayer•WC grains adjacent to interface•Strong interface

Back scattering SEM images

W coating

SiC

W+C

100

150

200

250

3 5 7 9 11Scan speed (mm/sec)

Flexural strength (MPa)

Without VDWith VD

Effect of Processing Condition onFlexural Strength of W Coated SiC

W coating side

Four point flexural testSpecimen size: 50x4x3 mmSupport span: 40 mmLoading span: 20 mmCrosshead speed: 10um/sec

Substrate strength

W coating was not peeled off during flexural testStrength of substrate SiC was decreased by IR processingVapor 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: 10HzMax. flux: 23.5MW/m2 (10ms)Min. flux: 5.9MW/m2(90ms)Substrate temp. (bottom):

600 ºC

Substrate material: silicon carbideCoating material: tungsten (50µm-

thick)Specimen size: 50 x 4 x 3 (mm)

W coated specimen

Cooling table

0

5

10

15

20

25

-200 0 200 400 600 800 1000Time (ms)

Heat flux (MW/m

2)

W+C




600 ºC



W coated specimen

Cooling table

0

5

10

15

20

25

-200 0 200 400 600 800 1000Time (ms)

Heat flux (MW/m

2)




600 ºC



W coated specimen

Cooling table

0

5

10

15

20

25

-200 0 200 400 600 800 1000Time (ms)

Heat flux (MW/m

2)

QuickTime™ and aDV/DVCPRO - NTSC decompressorare needed to see this picture.

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: 10HzMax. flux: 23.5MW/m2 (10ms)Min. flux: 5.9MW/m2(90ms)Cycle: 1000Substrate temp. (bottom): 600 ºC

Mapping “over-cooked” Coating (Higher Power, Slower Scan)

SiC

Wcoating

W

C

SiBack scattering electron image

EDS mappingof W, C, Si

W+C W+Si

Hexoloy SiC + W (no pretreatment)Lamp power: 2350 W/cm2

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

Documents

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)