Two-step hot pressing of bimodal micron/nano-ZrB2 ceramic with improved mechanical properties and thermal shock resistance

• The grain growth and densification behaviors were investigated.
• A bimodal micron/nano-ZrB2 ceramic was prepared by two-step hot pressing.
• The mechanical properties and thermal shock resistance were greatly improved.

The densification and grain growth behaviors for micron- and nano-sized ZrB2 particles were investigated. The densification on-set temperature (Td-micron) and grain growth on-set temperature (Tg-micron) for micron-sized ZrB2 particles were about 1500 °C and 1800 °C, respectively. And the densification on-set temperature (Td-nano) and grain growth on-set temperature (Tg-nano) for nano-sized ZrB2 particles were about 1300 °C and 1500 °C, respectively. A bimodal micron/nano-ZrB2 ceramic was therefore prepared using a novel two-step hot pressing. A high relative density of 99.2%, an improved flexural strength of 580.2 ± 35.8 MPa and an improved fracture toughness of 7.2 ± 0.4 MPa·m1/2 were obtained. The measured critical thermal shock temperature difference (ΔTc) for this bimodal micron/nano-ZrB2 ceramic was as high as 433 °C.