The influences of hot pressing parameters (sintering temperature, soaking time and applied external pressure) and amount of SiC addition as the reinforcement phase on the indentation fracture toughness (KIC) of ZrB2–SiC composites were investigated. A design of experiment approach by the Taguchi methodology was used to optimize the processing parameters of hot pressing temperature, soaking time, applied pressure and SiC content. Hence, an L9 orthogonal array including nine tests for the mentioned parameters with three levels for each parameter was designed. The fracture toughness values were estimated using the Anstis equation from the lengths of indentation-induced diagonal cracks by Vickers’ indenter. By analysis of variance calculations, the applied pressure was recognized as the most effective parameter on the fracture toughness of ZrB2–SiC composites. At the optimal processing conditions i.e. the sintering temperature of 1850 °C, the soaking time of 90 min, the applied pressure of 16 MPa and the SiC content of 25 vol%, a fracture toughness of 4.8 MPa.m½ was predicted. The confirmation test, fulfilled under the optimal conditions, revealed that the experimental result (4.6 MPa.m½) is near to the expected values by Taguchi prediction. Finally, the toughening mechanisms in hot pressed ZrB2–SiC composites were identified.
