TUNGSTEN FOAM: Bonding Options

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TUNGSTEN FOAMBonding Options
Shahram Sharafat and Nasr M. Ghoniem University
of California, Los Angeles (UCLA) High Average
Power Laser Program Workshop E-Meeting July 11,
2003
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W-Foam Bonding
W-Foam ODS Bond

• W-Foam/ODS maximum interface temperatures are low
  (lt 600oC)
• Some Bonding Options
• 1) Brazing
• 2) Pressurized Mechanical Interlocking3)
  Plasma Spraying
• 4) Diffusion Bonding

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1. Brazing

• Boeing developed brazing materials for
  Tungsten-metal bonds, capable of operating up to
  1200oC.
• Brazing materials can be applied using
  plasma-spraying.
• Sulzer supplies high operating temperature
  (lt1200oC) plasma spray-able Ni and Co brazing
  materials.
• Special W-Steel Braze materials may have to be
  developed.

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Brazing of W-Foam

• Plasma spray or CVD a face sheet onto the foam
• Braze the face-sheet to the substrate
• ULTRAMET routinely plasma sprays face-sheets on
  refractory foams
• - The plasma-sprayed face-sheet ends within the
  first layer of cells.
• - Pressure tests reveal that the face sheet does
  not separate from the foam (the foam fails
  away from the face sheet).

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2. Pressurized Mechanical Interlocking of W-Foam

• Plasma spray a face sheet with geometrically
  interlocking features
• Press-fit the foam/face-sheet onto ODS using high
  pressure gas (shrink-fit).
• May have to use brazing for improved
  performance

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2. Pressurized Mechanical Interlocking of W-Foam

• Tungsten or Molybdenum have been successfully
  used on ASDEX-U and C-Mod
• The results of the ITER development program have
  shown W on Cu can withstand up to 25 MW/m2without
  damage (500 cycles, 10s on 10s off)
• Tapered W-rods are driven into the Cu substrate
  and HIPPED

HAPLs FW
R. Nygren, et al., Fusion Engineering and Design
4950 (2000) 303308
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3. Plasma Spraying Tungsten

• To bond W-Foam to ODS a face sheet is needed
• Use plasma spraying or CVD to create the face
  sheet
• Using a high-power hollow cathode plasma gun, we
  have plasma sprayed tungsten coatings onto steel
  substrates
• Preliminary results show high densities and
  bubble-free interfaces

Interface Outline
A. Kobayashi , S. Sharafat, and N. Ghoniem,
Formation of Tungsten Coating by Gas Tunnel Type
Plasma Spraying, Vacuum, accepted for
publication, June 2003.
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PFC Plasma Spraying Tungsten

• Hino and Akiba reported on PFC for ITER using
  plasma spraying of tungsten
• To increase adhesion performance between a
  tungsten layer and a copper substrate, a pure
  tungsten layer and a functionally graded material
  (FGM) layer of tungsten-to-copper was produced
  using plasma spraying.
• A 5-mm thick pure tungsten layer with a 2.5-mm
  thick FGM layer was successfully produced on a
  copper heat sink.
• These plasma spray approaches show promise for
  HAPLs FW.

T. Hino, M. Akiba, Japanese developments of
fusion reactor plasma facing components, Fusion
Engineering and Design 4950 (2000) 97105
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PFC Plasma Spraying Tungsten
PFC
HAPLs FW
Plasma Spray Tungsten Face Sheet
W-Foam
W to Fe FGM Layer
Braze
ODS
T. Hino, M. Akiba, Fusion Engineering and Design
4950 (2000) 97105
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Summary

• First step plasma spray a W-face sheet onto
  W-foam
• Second step bond the face sheet to the substrate
  by
• Brasing
• Pressurized Mechanical Interlocking
• Both
• Plasma spraying of W is a well established
  process resulting in 90 dense W with 70
  thermal k of solid W