The effect of high temperature heat-treatment on the strength of C/C to C/C–SiC joints

Joining of carbon fiber reinforced carbon matrix composite to a carbon fiber reinforced C–SiC dual matrix composite has been realized through a reaction joining process using boron-modified phenolic resin with micro-size B4C and nano-size SiO2 powder additives. The effect of the heat-treatment temperature on the retained strength of the joints, calculated by dividing the strength of the heat-treated joints by the strength of the joints before heat-treatment, was studied. The maximum retained strength of the joints is 91.9% after heat-treatment at 1200 °C for 30 min in vacuum, indicating good heat-resistance of the joints. The interlayer with a thickness of about 25 μm is uniform and densified. There are no obvious cracks or pores at the interfaces. The interlayer is composed of B4C, SiO2, glassy carbon, B2O3 and borosilicate glass. Si diffuses from the interlayer into the substrates and reacts with carbon to form SiC. Both B and O migrate from the interlayer into the substrates, contributing to the interfacial bonding. The B4C and the SiO2 powder additives contribute to the densification of the interlayer, the bonding at the interfaces and the heat-resistance of the joints.