CVD of boron carbide as coating and matrix material

The authors have investigated the use of propylene as the carbon bearing component to deposit fully dense boron carbide on reinforcing fibers at temperatures lower than 1200°C and at relatively high (atmospheric) pressure. Substrates were polished graphite samples or SiC and graphite fiber preforms. Boron carbide formed by CVD was deposited as coatings of hardness >4000 kg/mm2. Amorphous material was obtained at 950°C. Under conditions of high saturation of the gas phase the deposition kinetics remain surface reaction controlled up to a temperature of 1150°C, when material having strong preferred orientation, with plane 110 parallel to the surface, is formed. The coatings are strongly conformal to the surface, penetrating into pores of graphite substrates and infiltrating voids between reinforcing fibers of SiC or carbon.