First principles calculations and synthesis of multi-phase (HfTiWZr)B2 high entropy diboride ceramics: Microstructural, mechanical and thermal characterization

First principles calculations were conducted on (HfTiWZr)B2 high entropy diboride (HEB) composition, which indicated a low formation energy and promising mechanical properties. The (HfTiWZr)B2 HEBs were synthesized from the constituent borides and elemental boron powders via high energy ball milling and spark plasma sin-tering. X-ray diffraction analyses revealed two main phases for the sintered samples: AlB2 structured HEB phase and W-rich secondary phase. To investigate the performance of multi-phase microstructures containing a sig-nificant percentage of the HEB phase was focused in this study. The highest microhardness, nanohardness, and lowest wear volume loss were obtained for the 10 h milled and 2050 degrees C sintered sample as 24.34 +/- 1.99 GPa, 32.8 +/- 1.9 GPa and 1.41 +/- 0.07 x 10-4 mm3, respectively. Thermal conductivity measurements revealed that these multi-phase HEBs have low values varied between 15 and 23 W/mK. Thermal gravimetry measurements showed their mass gains below 2% at 1200 degrees C.

Automated summary

First principles calculations were used to study the (HfTiWZr)B2 high entropy diboride and showed that it has low formation energy and promising mechanical properties. The synthesized samples exhibited high hardness and low wear volume loss. The multi-phase HEBs also demonstrated low thermal conductivity and low mass gain at high temperature.