Effect of Mo and TiC addition on the microstructure and mechanical properties of spark plasma sintered Si3N4 composites

In this study, to improve the fracture toughness of Si 3 N 4 ceramics and overcome the reduction in the hardness caused by toughening, the Si 3 N 4 -based composite ceramics were prepared by spark plasma sintering . Fixed amounts of Y 2 O 3 (7 wt%) and TiC (8 wt%) together with Mo adjusted in the range of 0-8 wt% were incorporated into the Si 3 N 4 matrix. Besides, Si 3 N 4 composites were also prepared as control groups by excluding TiC and Mo. The results reveal that the addition of TiC improves the hardness of the Si 3 N 4 composites by inhibiting the transformation from α-Si 3 N 4 to β-Si 3 N 4 and grain refinement. Meanwhile, the high hardness of the composites is maintained even after toughening with Mo. The addition of Mo promotes the nucleation and phase transformation of α-Si 3 N 4 by promoting the transfer of the Si and N atoms. At the same time, molybdenum silicide is formed in-situ, improving fracture toughness through various toughening mechanisms. The Si 3 N 4 composites with 8 wt% TiC and 8 wt% Mo sintered at 1700 °C exhibit the optimal properties, with Vickers hardness and fracture toughness determined to be 18.25 GPa and 10.2 MPa•m 1/2 , respectively.