One-step brazing process to join CFC composites to copper and copper alloy Milena Salvo a, * , Valentina Casalegno a , Stefano Rizzo a , Federico Smeacetto a , Monica Ferraris a , Mario Merola b a Materials Science and Chemical Engineering Department, Politecnico di Torino, C.so Duca degli Abruzzi 24, I-10129 Torino, Italy b ITER Organisation, Cadarache Centre, Bat 524, F-13108 Saint Paul lez Durance, France Received 25 April 2007; accepted 16 July 2007 Abstract The aim of this work is to develop a new single-step brazing technique to join carbon fibre reinforced carbon composite (CFC) to pure copper (Cu) and copper alloy (CuCrZr) for nuclear fusion applications. In order to increase the wettability of CFC by a copper-based brazing alloy containing no active metal, 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 CFC surface modification, the commercial Gemco Ò alloy (Cu/Ge) was successfully used to braze CFC to pure copper and pure copper to CuCrZr by the same heat treatment. The shear strength of the CFC/ Cu joints measured by single lap shear tests at room temperature was (34 ± 4) MPa, comparable to the values obtained by other joining processes and higher than the intrinsic CFC shear strength. Ó 2007 Elsevier B.V. All rights reserved. 1. Introduction 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 the plasma-facing com- ponents (PFCs). The PFCs are actively cooled thermal shields devoted to sustain the heat and particle fluxes dur- ing normal and transient operation conditions as well as during off-normal events. They consist of a plasma-facing material, the armour, which is made of either carbon fibre reinforced carbon composite (CFC) 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 CFC/Cu joint manufacturing are the large thermal expansion mismatch of the compo- nents and the bad wetting behaviour expressed by a very high contact angle of molten copper on carbon substrates. CFCs have excellent thermo-mechanical properties, such as high thermal conductivity, high thermal shock and thermal fatigue resistance. Thanks to these characteristics, the CFCs will be employed in ITER (International Thermonu- clear Experimental Reactor) as plasma facing components, which interact directly with plasma [1]. This paper deals with the realization of the CFC/ CuCrZr joint for the ITER divertor, which is the most crit- ical step in the manufacturing of this component. This joint must withstand the thermal, mechanical and neutron loads, the cyclic mode of operation, while providing an acceptable lifetime and reliability. Due to the large thermal expansion mismatch between the CFC and the copper alloy, a thin (1– 2 mm thick) soft interlayer made of pure copper is inserted between the CFC and the CuCrZr to alleviate the joint interface stress [2,3] generated during the working condi- tions. In the manufacturing process of the CFC to Cu joint, 0022-3115/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2007.07.010 * Corresponding author. Tel.: +39 (0)11 564 4706; fax: +39 (0)11 564 4699. E-mail address: milena.salvo@polito.it (M. Salvo). www.elsevier.com/locate/jnucmat Available online at www.sciencedirect.com Journal of Nuclear Materials 374 (2008) 69–74