Nanostructural and nanoindentation characterization of ZrB₂ ceramics toughened with in-situ synthesized ZrC

A near fully-dense ZrB₂–ZrC composite was produced by SPS of ZrB₂, Zr, and graphite powders. Advanced electron microscopy characterization was used to investigate the densification and sintering mechanisms, as well as the interfacial phenomena. Mechanical properties were studied through nano-indentation. The synthesis of ZrC is mainly controlled by a high fluidity liquid phase, which plays a crucial role in transferring the Zr atoms on the graphite flakes. Although such a liquid may be solidified as an amorphous interfacial phase during the cooling step, it effectively promotes composite toughening by a homogenous distribution of the in-situ synthesized phases. While a relatively weak hardness result (~11.3 GPa) was measured, a remarkably improved fracture toughness (~5.4 MPa.m^1/2) was achieved. The outcomes of nano-indentation confirmed the paradoxical influence of amorphous interfacial phase on the mechanical behavior. Related discussions about the toughening mechanisms, interfacial phenomena, and nano-indentation behavior were also included and graphically presented.