Temperature dependence of microstructure evolution during hot pressing of ZrB₂–30 vol.% SiC composites

Microstructure evolutions of ZrB₂–30 vol.% SiC composites, prepared by hot pressing at different processing temperatures (1700, 1850 and 2000 °C) for 30 min under 10 MPa, were investigated by optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM). The microstructures of the fabricated composites were compared with and the effects of the processing temperature on the sintering process and densification behavior during the hot pressing were found. The amount and the orientation of dislocations which were indicated by TEM analysis in the sample hot pressed at 1700 °C showed that no plastic deformation and atomic diffusion occurred. But the presence of amorphous phases and rearrangement of particles are signs of the fact that liquid phase sintering and particle fragmentation/rearrangement is the main densification mechanism. On the other hand, in the sample hot pressed at 1850 °C, aggregation of dislocations behind the grain boundaries and the presence of twinnings addressed wide plastic deformations which were introduced as the main densification mechanism at 1850 °C. Finally in the sample hot pressed at 2000 °C, lower amounts of un-oriented dislocations and also some annealing twinnings were observed in TEM micrographs together with fractographical SEM analysis and showed that the atomic diffusion is the dominant densification mechanism of hot pressed ZrB₂–30 vol.% SiC composite.