Chemistry of boron and silicon: applications to ceramic composite materials for high temperature uses

Henri Moissan, with his electric arc furnace, has been one of the very first researchers to produce refractory borides, carbides, nitrides and silicides, including SiC, B4C and BN. These materials are actually the constituents of the ceramic matrix composites (C/C, C/SiC and SiC/SiC), developed sixty years later for structural applications at high temperatures. However, ceramic matrix composites (CMCs) are fabricated at lower temperatures to take into account the fragility of the fibers. They consist of a ceramic fiber architecture densified, e.g. by chemical vapor infiltration, with a ceramic matrix, both constituents being coupled through an interphase material (graphitic carbon or hexagonal-BN) whose role is to deflect matrix microcracks and prevent the early failure of the fibers. CMCs are tough and damage-tolerant ceramics. Conversely, they are oxidation-prone. Their oxidation-resistance can be improved with the use of a coating or better with that of a multilayered self-healing matrix combining mechanical fuses (for crack deflection) and compounds forming fluid healing oxides.