Bulk titanium nitride ceramics - Significant enhancement of hardness by silicon nitride addition, nanostructuring and high pressure sintering

Dense nanocomposites consisting of titanium nitride (TiN) and 1.7-8.1 mol% silicon nitride (a-Si3N4) have been prepared by high-pressure sintering at 6.5 GPa and at temperatures up to 1300 °C. Microstructure, hardness, indentation fracture toughness, elastic modulus and the correlation of these parameters to the silicon nitride content of the obtained TiN-Si3N4 ceramics have been determined. The results demonstrate that even the addition of small amounts of Si3N4 leads to a considerable increase in Vickers hardness to HV500 g ∼ 25 GPa and indentation fracture toughness up to 6 MPa m½. This significant enhancement of mechanical properties can be related to interfacial bonds between titanium nitride crystals strengthened by nano-size effects and amorphous silicon nitride forming an intergranular matrix. Realignment and rotation of such interlocked titanium nitride crystallites under deformational stress is suppressed and crack propagation reduced by a crack deflection mechanism.