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R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh

University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255

R. G. Downing National Institute of Standards and Technology,

Gaithersburg, MD 20899-3460

Scott O’Dell

Plasma Processes, Inc., 4914 Moores Mill Rd., Huntsville, AL 35811

G. Romanoski, T. Watkins, L. Snead Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6138, USA

Helium Retention in nano-Porous Tungsten Implanted with Helium Threat Spectrum Mimicking IFE Reactor Conditions

•Summary of work coordinated by Nalin Parikh (UNC) and presented by Lance Snead at the October 30,31 High Average Powered Laser Program Review meeting at the Naval Research Laboratory, Washington D.C.

Outline of the Talk

• Introduction – IFE conditions & He threat spectrum• Objective – Minimizing He retention• Experimental facilities – UNC-CH / NIST• Previous results – 1.3 MeV 3He implantation• He threat spectrum implantation (100 – 500 keV)• Helium retention results of nano-HfC W samples• Carbon implantation in W to form W2C

• Ongoing and Proposed Research

OBJECTIVE

• Implant IFE helium threat spectrum in nano-porous HfC-W and study helium retention while mimicking IFE conditions.

• C+ Implantation in W to Form W2C and Study 3He Diffusion Through W2C layer.

Engineered Tungsten Armor Development

• Vacuum Plasma Spray (VPS) forming techniques are being used to produce engineered tungsten armor.

• The engineered tungsten is comprised of a primary tungsten undercoat and a nanoporous tungsten topcoat.

• Nanometer tungsten feedstock powder is being used to produce

the nanoporous tungsten topcoat.

• The resulting nanoporous topcoat allows helium migration to the

surface preventing premature failure.

Low ActivationFerritic Steel

Primary W Layer

Nanoporous W Topcoat

Schematic showing the VPSing of the engineered W armor.

SEM image showing nanometer W feedstock powder produced by thermal plasma processing. Analysis has shown the average particle size is less than 100nm. This is one of two nanometer W feedstock materials used to produce the nanoporous topcoat.

Engineered Tungsten Samples for Helium Implantation Experiments at UNC

• To evaluate the effectiveness of the nanoporous W topcoat to prevent helium entrapment, engineered W deposits were produced with and without the nanoporous W topcoat.

• For the samples without the nanoporous topcoat, two different micron size feedstock powders (-45/+20µm and -20/+15µm) were used to produce the primary W layer.

• For the samples with the nanoporous topcoat, two different nanometer size feedstock powders (500 nm and 100 nm) were used.

• HfC additions were made to the nanometer W feedstock powders to pin the grains and prevent grain growth.

Primary W Layer Nanoporous W TopcoatW(-45/+20µm)

Thickness: ~0.6mmW(-20/+15µm)

Thickness: ~0.6mmW(-45/+20µm) W(100nm) - HfC

Thickness: ~0.5mm Thickness: ~75µmW(-45/+20µm) W(500nm) - HfC

Thickness: ~0.5mm Thickness: ~50µm

V2-06-355 8

V2-06-450 8

None

Feedstock Powders Used to Produce the Engineered W ArmorID Number

No. of Samples

V2-06-443 8

V2-06-349 None 8

Experimental Facilities

UNC – Chapel Hill, NC• 2.5 MV Van de Graaff accelerator

3He implantation and helium retention measurements by nuclear reaction analysis (NRA) technique

• 200 kV Eaton Ion Implanter NV-3204High fluence C+ implantation to study WCx formationHigh fluence He+ implantation to study sputtering Irradiation Damage study of multilayer dielectric mirrors

NIST, Gaithersburg, MD• Nuclear reactor neutron source

Measure helium retention by neutron depth profiling (NDP) technique

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

Previous results of He retention in W

NRA results of 3He retention for single crystal and polycrystalline tungsten with a total dose of 1020 He/m2. Percentage of retained 3He compared to implanting and annealing in a single cycle.

• 1.3 MeV to a dose of 1020 3He/m2 at 850°C followed by a flash anneal at 2000°C

• Same total dose was implanted in 1, 100, 500, and 1000 cycles of implantation and flash heating

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

0.00

0.20

0.40

0.60

0.80

1.00

1.00E+17 1.00E+18 1.00E+19 1.00E+203He dose per cycle (m-2)

Rel

ativ

e 3 He

rete

ntio

n

Mono He in SCW

Threat Spec in PolyW

New work with helium threat spectrum

E0 He beam

Foil Tungsten

E = E0 – Efoil

t

• Degrade the monoenergetic beam by transmission through a thin Al foil

• Tilting the foil provides a range of degraded energies by varying the path length d through the foil

where = 0° is normal incidence

θ cos

t d

• Al stopping power: ~330 keV/micron

• 900 keV 3He beam through a 1.5 micron Al foil tilted 0 – 60°

• Degraded energies: 100 – 500 keV

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

Threat spectrum implantation conditions

IFE Helium Threat Spectrum

0 200 400 600 800 1000 1200 1400

Energy (keV)

Rel

ativ

e H

e flu

ence

• Implantation at 850°C with flash heating to 2000°C between implant steps or at the end of a single step implant. (Temp. measured by infrared thermometer.)

• Total helium dose is divided by the no. of stepsPartial dose is implanted as a threat profile with the sample at 850°CSample heating 850°C 2000°C 850°C (10 s cycle)

• Next implant step begins

• LabVIEW automates foil tilt motions to implant correct dose at each position and controls sample temperature via power controller and infrared thermometer

• NDP used to determine helium depth profiles and for comparison of total helium retention

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

• Technique: Neutron Depth Profiling (NDP) measures elemental concentration profiles up to a few micrometers in depth for elements that emit a charged particle following neutron capture. (R.G. Downing, et al., NIST J. Res. 98 (1993)109.)

• Elements Analyzed: boron, lithium, helium, nitrogen and several additional light elements with less sensitivity. • Sample Environment: In an evacuated chamber, samples are irradiated with a beam of low energy neutrons. A small percentage of the emitted reaction particles are analyzed by surface barrier detectors to determine their number and individual energies.• Principles: The emission intensity is compared to a known standard to quantitatively determine the elemental concentration. The emitted particles lose energy at a predicable rate as they pass through the film; the total energy loss correlates to the depth of the reacting nucleus.• Advantage: NDP is non-destructive - allowing repeated determinations of the sample volume following different treatment processes. • Neutron beam flux at sample: ~7.5x108 n/cm2-s• Beam area: from a few mm2 to ~110 mm2

• Reaction: NDP utilizes the 3He(n,p)T reaction (5333 barns) and produces 572 keV protons and 191 keV recoil tritons.

Neutro

n

Sample

bea

m

NDP Experimental Arrangement

NDNDPP

NDP of boron in siliconNDP of boron in siliconDepth range: 15 nm – 3.8 µmDepth range: 15 nm – 3.8 µm

Sample Dimension

TXRF

NDP

XRF

RBS

Det

ectio

n lim

it (a

t/cm

3)

TOF-SIMS

Dynamic SIMS

FTIR

1000 Å 1µm 10 µm 100 µm 1 mm 1 cm

1e22

1e20

1e18

1e16

1e14

1e12

Neutron monitor

He retention for 1020 He/m2 in nano-W(<100nm Particles)

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

He retention comparisons for 1020 He/m2

nano-porous (>500nm particles) W with HfC

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

Results of He3 Retention in nano-porous W Implanted with

Helium Threat SpectrumNano- porous W (<100 nm) samples showed very dramatic decrease in retention of He when high dose (1E20/m2) implanted sample was heated to 2000 C, 5 min.

- Results confirm diffusion data of Wagner and Seidman- Phys Rev Lett 42, 515 (1979)

Nano-cavity W (>500 nm) samples behaved very much like poly crystalline W.

- nano particle size too big to have effective diffusion.

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

Carbon implantation in W to form WCx

Shon Gilliam, Zane Beckwith, Richard Parker, Nalin Parikh (UNC-Chapel Hill)Greg Downing (NIST)Glenn Romanoski, Lance Snead (ORNL)Shahram Sharafat, Nsar Ghoniem (UCLA)

Why are we interested?• Carbon ion irradiation and high temperatures in the first wall may lead to

tungsten carbide formation

• The presence of WCx may affect helium retention characteristics

Objectives• Try to form W2C in W samples through high fluence implantation of C and

high temperature annealing

• Study how W2C effects hydrogen and helium retention/diffusion

Ion Beam Laboratory

University of North Carolina at Chapel Hill, NC

XRD Spectra of C+ implantation into W to form W2C under

various implantation conditions

• GM2 100 keV 1.4e19 C/cm2 at RT 2000C/5min.

• GM3 1.5 MeV 3.5e17 C/cm2 at RT 2000C/5min.

• P04637 (threat spectrum) 1e18 C/cm2 at RT 2000C/5min.

W2C

Formation

GM2

Summary of W2C formation study

• 100 keV C implantation shows new XRD peaks compared to unimplanted W

• Need to establish conditions for W2C formation for samples implanted with C threat-spectrum

• Need to confirm that new peaks indicate W2C formation

• XTEM to observe microstructure of new phase

• After the phase is identified, implant H and He threat spectra to study retention

Proposed Research

• Reproduce He3 retention in nano-porous W•In cooperation with Plasma processes, Inc. (Scott O’Dell) and NIST (G. Downing)

• Formation of Tungsten Carbide • UNC (Parikh,et al), ORNL (G. Romanoski) and UCLA (S. Sharafat, N. Ghoniem)

•Accrual of carbon in near surface volumes of tungsten.•Damage phenomena associated with the implantation of Carbon•Mobility of carbon to the W/steel interface by grain boundaries and splat boundaries (for plasma sprayed tungsten).  This route should be at least 10X faster than bulk diffusion through tungsten.

• Effect of Carbide on Diffusion and Surface Integrity•Implantation and carbide formation, UNC (Parikh, et al)

•Thermal Fatigue and Thermal Stability (Romanoski, et al ORNL)

•Modeling of diffusion and release of helium