Effect of graphene nano-platelet addition on the microstructure and spark plasma sintering kinetics of zirconium diboride

In this paper, the effect of graphene nano-platelet (GNP) addition on the microstructure and sintering kinetics of ZrB2 during spark plasma sintering (SPS) is presented. SPS was carried out at 1800 °C temperature and 50 MPa pressure. GNP addition resulted in an increase in the relative density from 84% to 97%. Retention of GNPs after SPS was confirmed through Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) in conjunction with X-ray diffraction (XRD) and Raman spectroscopy. The effect of GNP reinforcement on sintering kinetics, microstructure and mechanical properties (Vickers micro hardness and indentation fracture toughness) are discussed. The ZrB2 -GNP samples showed different activation energies at different temperature ranges which are explained based on the likely processes that are involved during sintering. Final stage of sintering exhibited lower activation energy during which the GNP aided grain boundary sliding enhancing the densification. Several toughening mechanisms such as GNP fracture, GNP shearing, GNP bending and GNP pullout were observed.