Effect of B4C, MoSi2, nano SiC and micro-sized SiC on pressureless sintering behavior, room-temperature mechanical properties and fracture behavior of Zr(Hf)B2-based composites

In the present paper, ZrB2–HfB2 composite was developed via a pressureless sintering method and SiC, MoSi2 and B4C powders were used as additives. In order to produce composite samples, ZrB2 is first milled for 2 h, afterwards the reinforcing particles were added. The mixture was formed by cold isostatic press (CIP) and, after the pyrolysis, it was sintered at 2100 °C and 2150 °C. In order to compare the effect of different additives on pressureless sintering behavior of ZrB2–HfB2 composite, the shrinkage percentage of samples was measured both before and after the sintering, and the microstructure of samples was examined using scanning electron microscopy (SEM), equipped with EDS spectroscopy. Bending test and resonance frequency method were used to measure the strength and the elastic modulus of the samples, respectively. The results show that samples containing MoSi2 and SiC nanoparticles had the maximum flexural strength and elastic modulus. Moreover, the flexural strength and elastic modulus of the samples increased as the sintering temperature rose from 2100 °C to 2150 °C, suggesting that a temperature increase leads to an improved sintering process.