Strong and tough HfC-HfB2 solid-solution composites obtained by reactive sintering with a SiB6 additive

HfC-HfB2 composite ceramics were successfully reactively spark plasma sintered with a unique SiB6 additive. The incorporation of the SiB6 not only promotes the densification of HfC (up to similar to 99%), but also significantly enhances the toughness from 4.3 +/- 0.5 MPa m(1/2) to 14.2 +/- 1.4 MPa m(1/2). The flexural strength of the HfC-HfB2 composite ceramics was simultaneously improved to 529 +/- 48 MPa, which is about 1.4 times higher than that of HfC. This improvement is attributed to the dense composite microstructure comprising an in-situ formed HfB2 and a solid solution of Si and O in HfC and HfB2 grains.