Enhanced Mechanical Properties and Oxidation Resistance of Zirconium Diboride Ceramics via Grain-Refining and Dislocation Regulation.

Zirconium diboride (ZrB 2 ) is considered as one of the most promising ultra-high temperature materials for the applications in extreme environments. However, the difficulty in fabrication of ZrB 2 limits its industrial applications. In this study, fully dense and grain-refined ZrB 2 is prepared under ultra-high pressure of 15 GPa at low temperature of 1450 °C. The as-prepared ZrB 2 exhibits excellent mechanical and oxidation-resistant properties. Compared with raw powder, the grain size decreases 56%. Compared with high-temperature sintered control specimen beyond 2000 °C, the hardness and fracture toughness increase about 46% and 69%, respectively, the dislocation density increase 3 orders of magnitude, while the grain size considerably decrease 96%. According to work hardening, Hall-Petch and Taylor dislocation hardening effects, the refined grains, substructures, and high dislocation density caused by plastic deformation during sintering can enhance the mechanical properties. The unique structure contributes to a threshold oxidation temperature increase of ≈250 °C relative to the high-temperature sintered ZrB 2 , achieving one of the highest values (1100 °C) among the reported monolithic ultra-high temperature ceramics. A developed densification mechanism of dislocation multiplication with grain refining is proposed and proved to dominate the sintering, which is responsible for simultaneous improvements in mechanical and oxidation-resistant properties.