Effect of HfB2 on microstructure and mechanical properties of ZrB2–SiC-based composites

• The results showed that Hf diffuses in ZrB2 and creates (Zr, Hf)B2 solid solution. By increasing sintering temperature and time, more Hf diffuses in ZrB2 and at result more solid solution creates.
• Pressure has less influence on diffusion rather than temperature and time.
• MoSi2 improves diffusion of Hf in ZrB2.
• HfB2 has negative effect on densification but improves flexural strength.

In this work, ZrB2–SiC-based composites with different additives were sintered in different temperature (1600, 1700, 1800 and 1900), time (4, 8, 12 and 16) and pressure (10, 20, 30 and 40 MPa). The effect of HfB2 (0, 5, 10, 15 vol.%) on ZrB2-based ceramics was investigated. Microstructure evaluation and phases were done by SEM and EDAX. Effect of SPS conditions (temperature, time and pressure) on microstructure was investigated. The results showed that Hf and Zr diffuse in each other and (Zr, Hf)B2 solid solution will be formed. In addition, it was concluded that by increasing temperature and time, solid solution formation increases. Pressure has little effect on diffusion. Also, MoSi2 and ZrB2 form (Zr, Mo)B2 solid solution. Finally it is cleared that HfB2 increases open porosity percent slightly. Finally, it was observed that HfB2 has negative effect on densification while improves flexural strength due to (Zr, Hf)B2 solid solution.