Effects of HfB2 addition on pressureless sintering behavior and microstructure of ZrB2-SiC composites

In this study the effects of HfB2 addition were investigated on the sintering behavior, densification and microstructure of ZrB2-SiC in the presence of B4C and MoSi2 as a sintering catalyst. 5, 10, 15 and 20 wt% of HfB2 was substituted with ZrB2 in ultra-high temperature ceramic composites of ZrB2-SiC. Additionally, the effect of using nano-scale against common micron size SiC was compared. All compositions were sintered for 1 h in 2100 °C and 2150 °C. Relative and bulk density and open porosity percentage of samples were calculated by Archimedes method. Dimensional changes of pellets and their weight reduction after pyrolysis and sintering proved that increasing of HfB2 leads to increasing of density and samples with MoSi2 gain higher density in comparison to others containing B4C. Phase studies specified by X-Ray diffraction showed the formation of ZrB2-HfB2 solid solution. Characterization and microstructure studies done by scanning electron microscopy revealed that microstructural properties improved by adding HfB2 up to 20 wt%.