Incorporation of BN-coated carbon fibers into ZrB2/SiBCN ceramic composites and their ablation behavior

ZrB2/SiBCN composites containing carbon fibers coated with BN were prepared using combination of sol-gel and spark plasma sintering (SPS) techniques. Thermal shock and ablation behavior of these composites were thoroughly analyzed. Sintered composites contained ZrB2, SiC and BN(C) crystalline phases. Thin BN layer passivated carbon fibers and prevented them from reacting with the matrix. With the addition of carbon fiber, diffusion coefficient decreased, and the thermal expansion coefficient increased in comparison to ZrB2/SiBCN composites without carbon fibers. Ablation tests showed no crack formation after carbon fibers were added to the composites. Ablation center exhibited loose and porous network structure. ZrSiO4 formed from ZrO2 and SiO2 reaction in the central ablation region. Presence of ZrSiO4 prevented samples from further ablation-related damages.