Toughening behavior in a carbon nanotube reinforced silicon nitride composite

The excellent mechanical properties of carbon nanotubes have been exploited recently to make structural nanocomposites with enhanced mechanical properties. Here silicon nitride ceramic matrix nanocomposites have been prepared with carbon nanotube (CNT) reinforcements using hot-pressing. Microstructures and mechanical properties are determined for these hot-pressed ceramics and are compared with a reference silicon nitride with no reinforcements. Hardness and fracture toughness are determined at room temperature using hardness indents produced by a macro-Vickers hardness indenter. Grain size and aspect ratio distributions and their impact on mechanical properties are presented. Rising R-curves are established for the CNT-reinforced silicon nitride demonstrating toughening behavior. Crack-bridging and CNT pullout are identified as toughening mechanisms.