Densification, microstructure, mechanical, and thermionic properties of spark plasma sintered LaB6–HfB2 composite

LaB₆–HfB₂ composites with the different HfB₂ contents (10 wt.%, 30 wt.%, 50 wt.%, 70 wt.%, and 90 wt.%) were densified by spark plasma sintering (SPS). Results showed that the densification mechanism of the composite transformed from the grain boundary diffusion into the dislocation climbing mechanism as the holding time was extended from 0 to 15 min under temperature range of 1750–1900°C. The HfB₂ phase could effectively limit the grain growth of LaB₆ phase, and the dynamic growth of the grain was governed by grain boundary diffusion. Both the Berkovich hardness and Vickers hardness obeyed the normal indentation size effect. LaB₆–70 wt.% HfB₂ composite had the highest fracture toughness of 3.98 ± .43 MPa m^.5, whereas the highest current density of 18.34 A/cm² belonged to LaB₆–30 wt.% HfB₂ composite. All the results demonstrated that LaB₆–HfB₂ composite was a promising material with the excellent structural and functional performance.