TUNGSTEN FOAM Bonding Options Shahram Sharafat and Nasr

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

W-Foam Bonding W-Foam ODS Bond 0. 5 mm ODS Steel 1 mm LAFS Steel 2 mm 1. W-Foam/ODS maximum interface temperatures are low (< 600 o. C): Ø Some Bonding Options: 1. 1) Brazing 2. 2) Pressurized Mechanical Interlocking 3) Plasma Spraying 3. 4) Diffusion Bonding

1. Brazing § Boeing developed brazing materials for Tungsten-metal bonds, capable of operating up to 1200 o. C. § Brazing materials can be applied using plasma-spraying. § Sulzer supplies high operating temperature (<1200 o. C) plasma spray-able Ni and Co brazing materials. AMDRY 914 Chemistry: Ni 20 Co 4. 5 Si 2. 8 B Particle Size: -106 +53 µm (-140 +270 mesh) Morphology: Spheroidal, Gas Atomized Processes: Braze, Properties & Applications: Chrome-free braze alloy with excellent ductility and high-temperature joint strength. Also offers excellent corrosion, oxidation and fatigue resistance. Exhibits good wetting and flow properties. Excellent choice for applications such as nickel and cobalt honeycomb structures, seals, wear rings and joints subject to high thermal and sonic fatigue. Also ideal for brazing copper plated, alloyed carbon or stainless steel components such as radiators and oil coolers. Strongest nickel-base braze alloy for components exposed to service temperatures of 870 - 1205°C (1600 - 2200°F). Special W-Steel Braze materials may have to be developed.

Brazing of W-Foam Plasma-sprayed Face Sheet 1. Plasma spray or CVD a face sheet onto the foam 2. 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). Plasma-sprayed Face Sheet Failure Region W-Foam ODS Braze Plasma-sprayed Permeable Face sheet (ULTRAMET)

2. Pressurized Mechanical Interlocking of W-Foam 1. Plasma spray a face sheet with geometrically interlocking features 2. Press-fit the foam/face-sheet onto ODS using high pressure gas (shrink-fit). Gas Pressure Braze W-Foam PS-W Face-sheet ODS Plasma-sprayed W Face-sheet ODS 3. May have to use brazing for improved performance

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/m 2 without damage (500 cycles, 10 s on 10 s off) Tapered W-rods are driven into the Cu substrate and HIPPED HAPL’s FW Braze W-Foam Plasma-sprayed W Face-sheet *R. Nygren, et al. , Fusion Engineering and Design 49– 50 (2000) 303– 308 ODS

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 180 um thick W- Coating A. Kobayashi , S. Sharafat, and N. Ghoniem, Formation of Tungsten Coating by Gas Tunnel Type Plasma Spraying, Vacuum, accepted for publication, June 2003.

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 HAPL’s FW. *T. Hino, M. Akiba, Japanese developments of fusion reactor plasma facing components, Fusion Engineering and Design 49– 50 (2000) 97– 105

PFC: Plasma Spraying Tungsten PFC HAPL’s FW Plasma Spray Tungsten Face Sheet W-Foam W to Fe FGM Layer Braze ODS T. Hino, M. Akiba, Fusion Engineering and Design 49– 50 (2000) 97– 105 11/9/2020 9

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 11/9/2020 10