Graphite nanoplatelets toughened zirconium carbide ceramics prepared by spark plasma sintering

Abstract

Zirconium carbide (ZrC) ceramics is an important candidate material for structural applications both at high temperature and intensive irradiation. However, its sensitivity to defects and cracks often causes low reliability and limited the application of ZrC ceramics. In this work, graphite nanoplatelets (GNPs) doped zirconium carbide ceramics were prepared by spark plasma sintering (SPS). The results show that the addition of GNPs not only improved the densification of ZrC ceramics but also inhibited grain growth of ZrC matrix phase. The GNPs were mainly located at the grain boundaries, and the c-axis of the disk-like GNPs preferred to align with the applied pressing direction during SPS. The preferred orientation of GNPs in the sintered ceramics resulted in anisotropic microstructure and fracture toughness of the material. Compared with the monolithic ZrC ceramics with a fracture toughness of 2.27 MPa m1/2, GNPs doped ceramics shows higher fracture toughness. The fracture toughness of ZrC ceramics with 0.5, 1.5, 3 vol% GNPs are 2.70 MPa m1/2, 3.03 MPa m1/2 and 3.24 MPa m1/2 measured on the surface perpendicular to the applied pressing direction and 3.43 MPa m1/2, 3.66 MPa m1/2 and 4.55 MPa m1/2 measured on the surface parallel to the applied pressing direction, respectively. The crack deflection and re-initiation by GNPs are the main toughening mechanisms for the GNPs doped ZrC ceramics.