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

The controlling densification mechanisms of hot pressed monolithic ZrB2 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 degrees 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 degrees C and plastic deformation of ZrB2 grains was nominated as controlling densification mechanism. Reduction of porosity in the hot pressed specimens at 2000 degrees 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. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.