Pre-Brazed Casting: A New Method to Join CFC Composite to Copper for the Manufacturing of Small Scale Monoblock Mockups

E. Visca (Sp), S. Libera, A. Mancini, A. Pizzuto, ENEA, Frascati (Italy) 
ENEA is involved in the European International Thermonuclear Experimental Reactor (ITER) R&D activities and in particular for the manufacturing of high heat flux plasma-facing components (HHFC), such as the divertor targets, the baffles and the limiters: During the last years ENEA has manufactured actively cooled mock-ups by using different technologies, namely brazing, diffusion bonding and hot isostatic pressing (HIPping). A new manufacturing process has been set up and tested. It was successfully applied for the manufacturing of W armoured monoblock mockups. This technique is the HRP (Hot Radial Pressing) based on performing a radial diffusion bonding between the cooling tube and the armour tile by pressurizing only the internal tube and by keeping the joining zone in vacuum and at the required bonding temperature. The heating is obtained by a standard air furnace.
The next step was to apply the HRP technique for the manufacturing of CFC armoured monoblock components. For this purpose some issues have to be solved like as the low CFC tensile strength, the pure copper interlayer between the heat sink and the armour necessary to mitigate the stress at the joint interface and the low wettability of the pure copper on the CFC matrix.
This paper reports the research path followed to manufacture a small scale CFC armoured mockup by HRP. An ad hoc rig able to maintain the CFC in a compressive constant condition was also designed and tested.
The casting of a soft copper interlayer between the tube and the tile was performed by a new technique: the Pre-Brazed Casting (PBC, ENEA patent).
A mock-up with three NB31 CFC tiles was successfully manufactured and it was tested in the TSEFEY-M electron beam facility at St. Petersburg (Russia). It reached 1000 cycles at 25 MW/m2 without suffering any damage.
This activity was performed in the frame of an IETR-EFDA contract.

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