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 degrees 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/cm(2) 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.