Fabrication and properties of HfB2 ceramics based on micron and submicron HfB2 powders synthesized via carbo/borothermal reduction of HfO2 with B4C and carbon

• This work is first to report on liquid nitrogen to refine HfB2 powders.
• The uniform submicron HfB2 powders were firstly synthesized.
• The quenching could break the HfB2 particles.
• FEA was used to explore the temperature and thermal stress.

The two batches of commercially available powders were used as raw materials to synthesize HfB2 powders. The synthesized HfB2 powders were heated at 450 °C for 10 min in the flow of nitrogen and then quenched into liquid nitrogen. The results indicated the refinement effect of liquid nitrogen quenching on synthesized HfB2 powders was very obvious. The relative density values of HfB2 ceramics fabricated using micron and submicron HfB2 powders were less than 89.5% due to the presence of trace carbonaceous compound and more than 98.1% due to higher driving force for densification, respectively. The microstructure, mechanical properties and thermal shock resistance of HfB2 ceramics fabricated using micron and submicron HfB2 powders were investigated in detail. In particular, finite element analysis was used to explore the temperature and thermal stress distribution in the specimen in the course of thermal shock.