Effect of addition of micron-sized TiC particles on mechanical properties of Si3N4 matrix composites

The effect of micron-sized TiC particles on mechanical properties of Si3N4 matrix composites was investigated. Si3N4TiC composites were fabricated by using powder metallurgy and gas pressure sintering (GPS) methods. In order to achieve high mechanical properties, the experimental data were carried out with five different Si3N4TiC contents. Hardness, fracture toughness and relative density of Si3N4TiC composites were characterized. The result indicated that the highest relative density (98.0%) and fracture toughness (KIC = 8.4 MPa m1/2) were measured for monolithic silicon nitride and 5 wt% TiC, respectively. Qualitative and quantitative phase compositions were analyzed by X-ray diffraction (XRD). The experimental analyses indicated that the TiC phase reacted with Si3N4 during the liquid phase sintering, resulting in formation of TiC0.3N0.7. The phase transition, crystal growth, microstructure and mechanical properties of composites were investigated by scanning electron microscopy (SEM). Due to the inhibition of the grain growth, the aspect ratio exhibited a higher value from SNT0 (aspect ratio = 4.54) to SNT5 (aspect ratio = 5.60). The toughening mechanism of Si3N4TiC composites was attributed to crack deflection and crack impedance by periodic compressive stress in the Si3N4 matrix. However, the increase of the TiC content easily led to excessive connection microcrack, which would not be beneficial for the strength.