Elaboration of Cu/ C composites

Several processes have been developed to elaborate copper carbon composites through hot pressing or squeeze casting [Praksan et al., 1997][Korab et al., 2002]. However, all processes are difficultly perfecting and too expensive for elaboration of thin sheet materials. Besides, the poor wettability of carbon fibres with copper lead to low interfacial strength of composites obtained with casting or liquid process routes. This low wettability results often by large angle of the copper drop on graphite substrate (fig 2.). Then, one solution is the improvement of this wettability between copper and graphite with alloying element with

copper melt, such as Cr or Ti, in order to create a carbide layer to the copper/carbon interface [Goni, 1998]. Then, the wetting angle decreases from 137° for the pure copper to 46° for the alloy Cu-1%wt Cr. This alloy has a good wettability with a final wetting angle lower than 90° because of the formation of chromium carbide (Cr3C2) layer in the copper/carbon interface.

0 — 145°> 90° і—> Low wettability Fig. 2. Wetting angle of copper on graphite substrate.

Currently, the elaboration processes of Cu/C composites are based on powder metallurgy technology that offers many advantages such as the decrease of the machining cost (economical aspect), of power consummation (environmental aspect), and the better interfacial properties between copper matrix and carbon fibres. In opposite, the squeeze casting or liquid process route involves the low melting of matrix, low reactivity of metal liquid with carbon reinforced, and good wettability of metal liquid with carbon fibres. Indeed, the no reactivity between carbon and copper leads to very low mechanical resistance of the interface and poor mechanical properties of composite. In order to improve the mechanical properties of interface, the carbon fibres require a previous surface treatment. These surface chemical treatments (in different acid solutions) of the carbon fibres, which may be used in order to create chemical bonding at the C-Cu interfaces, will be presented in more details in the following sections.