The influences of processing variables on densification, grain growth and hardness of hot pressed ZrB2 based composites, reinforced with different amounts of SiC and short carbon fibers (Csf), were investigated. Taguchi methodology was employed as the design of experiments to study the properties of ZrB2–SiC–Csf composites. Hot pressing parameters (sintering temperature, dwell time and applied pressure) and the amount of additives (vol% SiC / vol% Csf) were specified as the variables. The microstructural analysis by SEM showed that Csf acts as a sintering aid through eliminating the oxide impurities the surfaces of starting materials. In addition, the in-situ formation of interfacial ZrC phase assisted the sintering process of ZrB2-based ceramics. Removal of oxide impurities and the presence of ZrC hindered the growth of ZrB2 grains, similar to the pinning of grain boundaries by SiC. Analysis of variance (ANOVA) recognized the sintering temperature as the most effective variable on the relative density, mean ZrB2 grain size and hardness of hot pressed composites. After sintering temperature, SiC/Csf ratio (composition) was identified as the second effective variable on the relative density and grain size, however, the composition did not remarkably affect the hardness. The applied external pressure and dwell time had not significant effects on the investigated properties
