Fractographical assessment of densification mechanisms in hot pressed ZrB₂-SiC composites

The controlling densification mechanisms of hot pressed monolithic ZrB ₂ ceramics and ZrB₂-based composites, containing 15 and 30 vol% SiC, at different consolidating temperatures were investigated, based on scanning electron microscopy micrographs of fracture surfaces, relative densities, and average grain size of ZrB₂. For the hot pressed samples at 1700 °C, particles fragmentation in the composite samples, mechanical interweaving, and rearrangement without sizeable chemical bonding were appointed as dominant densification mechanisms. Neck formation between ZrB₂/ZrB₂ was observed at 1850 °C and plastic deformation of ZrB₂ grains was nominated as controlling densification mechanism. Reduction of porosity in the hot pressed specimens at 2000 °C was related to grain boundary diffusion mechanism. Colossal grain growth in monolithic ZrB₂ ceramic proposed the occurrence of detrimental mechanisms such as grain coarsening and evaporation/condensation. Presence of intergranular SiC particles between ZrB₂ grains impeded extremist grain growth.