Engineered Tungsten Surfaces for IFE Dry Chamber Walls

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Engineered Tungsten Surfaces for IFE Dry Chamber
Walls
Scott ODell

• Plasma Processes Inc.
• 4914 Moores Mill Road
• Huntsville, AL 35811

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Introduction

• Tungsten is an ideal material for armoring IFE
  dry chamber walls.
• High melting temperature
• Low thermal erosion
• Techniques for accommodating cyclic energy
  deposition are needed.
• In addition, elimination of helium build-up is
  desired to prevent premature armor failure.

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Solution

• Use a functional gradient material to join the
  tungsten armor to low activation ferritic steel
  walls
• Minimize stress at the interface due to CTE
  mismatch
• Provide short transport path for removal of
  helium
• Nanometer grain structure to promote grain
  boundary diffusion (GB diffusion gt Bulk
  diffusion)
• Interconnected nanometer size porosity
• PPI and UCSD has been awarded a DOE STTR Grant to
  develop Engineered Tungsten Armor using advanced
  Vacuum Plasma Spray (VPS) forming techniques

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Vacuum Plasma Spray

• Plasma Processes, Inc. is a small business that
  specializes in the development and fabrication of
  refractory metals and advanced ceramic materials
  for High Heat Flux (HHF) applications.
• Innovative Vacuum Plasma Spray (VPS) forming
  techniques are used to produced
• Complex components to near net shape
• Advanced high temperature coatings and composite
  materials
• Join materials with dissimilar CTEs

Nano-grained, porous W (1-2 microns thick)
Dense W Functionally Graded to Ferritic Steel
Low Activation Ferritic Steel
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VPS Formed Refractory Metal Components

• Plasma facing component heat sinks with in-situ
  formed helical fins
• Thin-walled closed end refractory metal
  cartridges with ceramic liners for processing
  samples in microgravity (leak rate of lt1x10-8
  sccs He)
• Nozzle inserts to reduce/eliminate throat erosion
  solid rocket engines

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Joining of Materials with Dissimilar Coefficients
of Thermal Expansion

• Gradual transition from one material to the other
  reduces stress as compared to a typical sharp
  interface.
• Ability to use coatings that enhance bonding
  between the armor and the substrate.
• Recently functional gradients have been used to
  join thick (3-5mm) VPS W deposits to actively
  cooled Cu alloy heat sinks for MFE PFCs.

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Medium Scale MFE PFC Armored with VPS Tungsten
Medium Scale after Armor Castellation (top view
of 0.4m long PFC)
Deposition of VPS W Armor
Close-up of Castellated Armor
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Influence of Particle Size on VPS W
B
C
A
Average starting particle size A) 26µm B)
13µm C) 3µm Micrographs demonstrate by
reducing the starting powder size the grain
structure of the resulting deposit can be reduced.
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Ultrafine Grained VPS W

• Submicron W powder (0.5µm)
• Transition metal carbides to pin the grain
  boundaries (HfC)
• VPS formed W components with ultrafine grained
  structures have been produced.

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Porous VPS Tungsten

• By controlling the deposition parameters, porous
  deposits can be produced.
• Porous W deposits between dense W layers have
  been produced for use as helium cooled heat
  sinks.
• Helium flow tests have demonstrated the porosity
  is interconnected.
• Size of porosity is highly dependent on the size
  of the starting powder.

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He Cooled W Heat Sink
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Engineered W Surfaces for IFE Dry Chamber Walls

• Develop a preliminary model to aid in the design
  and optimization of engineered W
• Develop VPS fabrication techniques based on
  functional gradient materials for joining
  engineered W to low activation ferritic steel
• Produce engineered W surfaces comprised of
  nanometer size grains and interconnected
  nanometer porosity to eliminate He entrapment
• Demonstrate migration of helium
• through the engineered tungsten surface
• Produce samples for thermal cycle
• testing and analysis

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Tungsten Brush Armor for MFE PFCs

• PPI, SNLs and Boeing have worked to develop W
  brush armor for MFE PFCs
• PPI was the first to produce medium scale PFCs
  with W brush armor (PW-8 and PW-14)
• 32mm x 100mm armor area comprised of 10mm tall W
  rods
• Medium scale mockups have been thermal response
  tested to 23 MW/m2
• Survived 500 thermal cycles at 20 MW/m2

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Insulator Coating for the University of
Washingtons HIT Device

• In a recent effort for the University of
  Washington, PPI applied an alumina dielectric
  coating on plasma facing surfaces of the Helicity
  Injected Torous (HIT) device.

HIT-SI components before deposition of
dielectric coating ..
The Helicity Injected Torus with Steady Inductive
Helicity Injection (HIT- SI) is a new spheromak
under construction at the University of
Washington. HIT- SI has several unique features,
the most notable being the bow tie cross-
section of the confinement region and the
presence of two semi- toroidal helicity injectors
at each end.
Inner cone after deposition of dielectric
alumina coating