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).