Electron microscopy investigation of spark plasma sintered ZrO₂ added ZrB₂–SiC composite

The impact of introducing nano-sized ZrO₂ additive on the sinterability and microstructure development of ZrB₂–SiC composite was studied. The spark plasma sintering (SPS) technique was selected as the manufacturing method, and the as-sintered sample reached a relative density value slightly higher than 98.5%. Advanced electron microscopy techniques along with X-ray diffraction (XRD) were used to characterize the final composite. The XRD assessment revealed the formation of two in-situ phases, namely ZrC and ZrSiO₄, along with the initial phases. Thermodynamic evaluations suggested the possible formation of a liquid phase due to interactions among the available oxides (e.g., ZrO₂, SiO₂, and B₂O₃). This assumption was fortified by the presence of an amorphous phase in the scanning electron microscopy (SEM) analysis. Finally, transmission electron microscopy (TEM) verified the formation of such a phase, consisting of a glassy B–Si–O bed with nano-sized crystalline particles (ZrSiO₄ and ZrC).