Characteristics of multi-walled carbon nanotube toughened ZrB₂-SiC ceramic composite prepared by hot pressing

Monolithic zirconium diboride ceramic as well as ZrB₂-20 vol% SiC and ZrB₂-20 vol% SiC-10 vol% carbon nanotube ceramic matrix composites were hot pressed at 1850 °C for 60 min under 20 MPa. The effects of adding carbon nanotubes on the densification process, microstructural development, and mechanical properties of ZrB₂-SiC were investigated. The results showed that the relative density and the mean ZrB₂ grain size in the final microstructure did not change significantly by adding 10 vol% carbon nanotube to the ZrB₂-20 vol% SiC composite. Compared to the monolithic ZrB₂, the grain growth was effectively stopped when the composite was reinforced by SiC and was doped with carbon nanotubes. Indentation fracture toughness of the carbon nanotube reinforced sample was measured about 5.1 MPa m, which is meaningfully higher than those of unreinforced ceramics. The remaining nanotubes in the final microstructure also led to the activation of some toughening mechanisms such as carbon nanotubes pull out and crack deflections. On the other hand, the Vickers hardness value (8.6 GPa) decreased due to the presence of carbon nanotubes as a soft reinforcement phase.