Microstructure and Mechanical Properties of TiB2-CNTs Composites Prepared by Spark Plasma Sintering

The study investigated the effect adding various amounts of carbon nanotubes (CNTs) had on the densification, the microstructures, and the mechanical properties of the TiB2 that was spark plasma sintered at 1750 degrees C for 5 min at 30 MPa. The CNT clusters that were pinned at the grain boundaries improved the densification and inhibited the grain growth. The test data revealed the strength initially increased from 508 +/- 18 MPa for monolithic TiB2 to 772 +/- 14 MPa for TiB2-5 wt% CNTs and a subsequent decrease as further increments of the CNTs amount were added. The results were consistent with the variation of the relative density and were inconsistent with the variation of grain size. The TiB2-5 wt% CNTs had an improved fracture toughness of 9.4 +/- 0.2 MPa . m(1/2), which was attributed to the additional CNTs that activated the toughening mechanisms, such as crack deflection, crack bridging, CNTs de-bonding and pull-out.