Optimization of SPS Parameters and Graphene Content with the Aim of Improving Densification and Flexural Strength of ZrB₂-SiC Composites

This study aims to investigate the significance of spark plasma sintering (SPS) variables and the number of graphene nanoplatelets (GNP) on the densification, flexural strength, and microstructure of ZrB₂-25 vol.% nano-sized SiC ceramics. Analysis of variance (ANOVA) and Taguchi method were conducted to find the optimal value of selected parameters on three levels. The three-point bending test and Archimedes principles were chosen to calculate flexural strength and relative density, respectively. Scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) were employed for the microstructural/phase investigations. Nearly full densification (99.8 ± 0.1%) and the highest flexural strength (610 ± 43 MPa) with 6.4 µm mean grain size were obtained at optimum SPS parameters (1900°C, 6 min holding time, and 20 MPa external pressure) by adding 7.5 wt.% GNP.