Effect of SiC morphology on characteristics of ZrB۲ ceramics fabricated by spark plasma sintering

In this research work, the effects of silicon carbide (SiC) as the most important reinforcement phase on the densification behavior and mechanical properties (hardness and indentation fracture toughness) of zirconium diboride (ZrB۲)-based ultra-high temperature ceramic composites were studied. In this way, a monolithic ZrB۲ ceramic (as the baseline) and three ZrB۲-based ceramic matrix composites, reinforced with ۲۵ vol% SiC in different morphologies (SiC particulates, SiC whiskers and mixture of SiC particulates/SiC whiskers), were fabricated by spark plasma sintering (SPS) route. The sintering process was carried out at a temperature of ۱۹۰۰ œC for a dwell time of ۷ min under an externally applied pressure of ۴۰ MPa in vacuum conditions. After spark plasma sintering, a relative density of ~۹۶% was obtained (using the Archimedes principles for evaluation of bulk density and the rule of mixtures for calculation of theoretical density) for the monolithic ZrB۲ ceramic sample, but the other ZrB۲-SiC composite samples approached their theoretical densities (relative density of ~۱۰۰%). The hardness and indentation fracture toughness values of the SiC reinforced ZrB۲-based samples were higher than those measured for the monolithic one. The simultaneous addition of SiC particulates/whiskers showed a synergistic effect on the enhancement of mechanical performance of ZrB۲-based composites.