Preparation of C/C-Cu composites from C/C by first modifying the precursor with Mo₂C

Two C/C preforms were prepared by the chemical vapor infiltration of pyrocarbon into needle-punctured carbon fiber felts to a density of 1.5 g/cm³, followed by or without graphitization at 2300℃. The two preforms were first treated in a KCl-LiCl molten salt mixture (mol/mol=59:41) containing 10 wt% ammonium molybdate at 1000℃ for 1 h to form a Mo₂C layer on pore walls of the preforms, then leached with deionized water to remove the KCl and LiCl, and finally vacuum-infiltrated with liquid copper at 1200℃ for 1 h to obtain C/C-Cu composites. Results indicate that the thicknesses of the Mo₂C layers are 2.5 and 3 μm for the preforms with and without graphitization, respectively. The Mo₂C layer improves the wetting of the pore walls by copper, which makes the copper infiltration complete. Local Raman spectroscopy shows that the intensity ratio of the G and D bands of the pyrocarbon is higher near carbon fibers while this trend is reversed after the molten salt treatment, indicating that the Mo₂C layer causes catalytic and stress-induced graphitization effects for the pyrocarbon in both preforms.