Hardness and toughness of hot pressed ZrB₂-SiC composites consolidated under relatively low pressure

ZrB₂-based composites, containing 15, 20, 25, and 30 vol% SiC, have been prepared by hot pressing at temperatures of 1700, 1850 and 2000°C for 30 min under a relatively low pressure of 10 MPa. Densification and mechanical properties of ZrB₂-SiC composites have been investigated. Fully dense ZrB₂-30 vol% SiC composite with a relative density of 99.8% is obtained at 2000°C. The highest values of Vickers hardness (21.3 GPa) and fracture toughness (4.7 MPa m^1/2) belong to this sample. Vickers hardness increases exponentially as the relative density of composite increases. A simplified equation was developed for the Vickers hardness of the investigated ZrB₂-SiC composites as a function of relative density and SiC content. Microstructural investigation by means of optical and scanning electron microscopy shows that by addition of SiC particles, some toughening mechanisms such as crack deflection, crack branching, microcracking, crack bridging, break of large SiC grains, and crack arresting by porosity are appeared.