M. Ferraris (Sp), A. Ventrella, V. Casalegno, M. Salvo, Politecnico di Torino (Italy); M. Merola, ITER
Organisation, Cararache Centre (France)
The ITER machine is an international effort aimed at demonstrating the scientific and technological feasibility of
fusion energy. One of the most technically challenging components of the ITER machine is the divertor; it includes
the cassette body (CB) and three plasma-facing components (PFCs), namely the inner and outer vertical target
(VT), and the dome (DO).
The PFCs are actively cooled thermal shields devoted to sustain the heat and particle fluxes during normal and
transient operations as well as during disruption events.
They consist of a plasma-facing material, the armour, which is made of either carbon fibre reinforced carbon
composite (C/C) or tungsten (W). The armour is joined onto an actively cooled substrate, the heat sink, made of
precipitation hardened copper alloy CuCrZr.
The main problems in the C/C-Cu joint manufacturing are the large thermal expansion mismatch of the
components and the very high contact angle of molten copper on carbon substrates.
The aim of this work is to develop a new single-step brazing technique to join C/C composite to pure copper and
copper alloy. The brazing of the three materials (C/C-Cu-CuCrZr) can be performed in a single heat treatment
using the same Cu/Ge braze.
In order to increase the wettability of C/C by the copper-based brazing alloy, the composite surface was modified
by direct reaction with chromium, which forms a carbide layer and allows a large reduction of the contact angle.
After the C/C surface modification, the commercial Gemco® alloy was successfully used to braze C/C to pure
copper and pure copper to CuCrZr by the same heat treatment.
The shear strength of the C/C-Cu joints, measured by single lap shear tests at room temperature, was 34 MPa,
comparable to value obtained by other joining processes and higher than the intrinsical C/C shear strength.