Synthesis and characteristics of the B4C–ZrB2 composites

Bulk ceramic materials based on B4C–ZrB2 systems have been produced by means of pressure-assisted Self-propagating High temperature Synthesis (SHS) using a mixture of elementary powders B, C and Zr. Reactant mixture compositions were chosen based on thermodynamic calculations to obtain synthesis regimes with the formation of a liquid phase, ensuring proper compaction. The liquid phase in the SHS products consisted from molten B4C. The influence of a chemical oven on densification of the SHS-products was studied. Significant reducing of ceramic residual porosity was obtained at mass ratio of the reaction mixture and the «chemical oven» 1 : 4. The minimum residual porosity of SHS composites obtained by a "chemical oven" is 1.7 %. X-ray analysis showed that SHS products were equilibrium and contain refractory compounds ZrB2 and B4C, which formed a dispersed phase and a ceramic binder. The influence of the composition of the reaction mixture on the formation of the microstructure and phase composition of ceramic composites was studied. It is established that microstructure of SHS-composites depends on the B4C content. At the B4C content less than 10 % wt. the B4C–ZrB2 ceramic composite has uniform microstructure with ZrB2 grain sizes of 10 – 20 µm. Increasing of the B4C contents up to 20 % wt. leads to decreasing of the ZrB2 grain size up to 2 - 5 µm. Vickers Hardness of the SHS composites are 21–24.5 GPA.