Spark plasma sintering of ZrB₂-based composites co-reinforced with SiC whiskers and pulverized carbon fibers

Spark plasma sintering (SPS) process was used to preparation of ZrB₂-based composites co-reinforced with SiC whiskers as well as various amounts of pulverized carbon fibers. The effects of C_F content on microstructure and mechanical characteristics of ZrB₂–SiC_w–C_F composites were scrutinized. Although all composites approached high densification, a fully-dense sample was fabricated by the addition of 2.5 wt% C_F. The growth of ZrB₂ grains was remarkably inhibited in C_F-reinforced composites. No in-situ formed phase was detected by XRD; however, trace of nano-ZrC clusters was observed in SEM fractographs of ZrB₂–SiC_w–C_F samples. The formation of such nano-sized ZrC refractory phase was also proved by thermodynamics. The hardness of composites slightly decreased from 21.9 to 19 GPa with increasing the C_F content. Reversely, the fracture toughness values enhanced from 4.7 to 6 MPa.m^½ with increasing the amount of pulverized carbon fibers.