TUNGSTEN FOAM: Bonding Options

1. 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

2. W-Foam 0.5 mm ODS Steel 1 mm LAFS Steel 2 mm W-Foam Bonding W-Foam ODS Bond • W-Foam/ODS maximum interface temperatures are low (< 600oC): • Some Bonding Options: 1) Brazing 2) Pressurized Mechanical Interlocking3) Plasma Spraying 4) Diffusion Bonding

3. 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 (<1200oC) plasma spray-able Ni and Co brazing materials. Special W-Steel Braze materials may have to be developed.

4. Plasma-sprayed Face Sheet Failure Region Plasma-sprayed Face Sheet W-Foam Braze ODS Plasma-sprayed Permeable Face sheet (ULTRAMET) 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).

5. Gas Pressure Braze W-Foam PS-W Face-sheet ODS Plasma-sprayed W Face-sheet ODS 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

6. Braze W-Foam Plasma-sprayed W Face-sheet ODS 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 HAPL’s FW *R. Nygren, et al., Fusion Engineering and Design 49–50 (2000) 303–308

7. 180 um thick W- Coating 80 um thick W- Coating 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.

8. 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

9. 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

10. 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