Effect of Carbon Nanotubes and Graphene Nanoplatelets on the Mechanical Properties of Zirconia-Based Composites

In this work, ZrO
₂
composites reinforced by single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP) were investigated. Composites were prepared by spark plasma sintering at a temperature of 1500°C. The influence of various carbon nanomaterials (CNM) on the microstructure, densification, microhardness, fracture toughness and crack propagation of zirconia-based composites was investigated. It is found that CNMs retain their structure after high-temperature sintering. The maximum increase in fracture toughness from 4.0 MPa·m
^1/2
to 5.5 MPa·m
^1/2
is found for a composite with SWCNTs. However, GNPs seem more effective as reinforcement than SWCNTs and MWCNTs, because the ZrO
₂
/GNP composite has an increased density (99.4%) and fracture toughness (5.2 MPa·m
^1/2
) compared to ZrO
₂
ceramics and in addition, the microhardness is not so much reduced in comparison with the ZrO
₂
/SWCNT composite.