Microcracking and R-curve behavior in SiC-TiB_2 composites

The fracture toughness of SiC-TiB_2 composites is studied as a function of TiB_2 size and fraction with emphasis on the effect of stress-induced microcracking. R-curve behavior in these materials is observed from double cantilever beam tests and is found to be a major strength-controlling factor. The microcrack process zones are confirmed by both small angle X-ray scattering and transmission electron microscopy. The process zone size scales with the fraction of TiB_2 present. For composites containing fine TiB_2 particles, quasi-catastrophic crack growth and arrest are observed during R-curve measurements. The various contributions to the R-curve are discussed.