Microstructure and mechanical properties of α/β-Si3N4 composite ceramics with novel ternary additives prepared via spark plasma sintering

In this study, alpha/beta-Si3N4 composite ceramics with high hardness and toughness were fabricated by adopting two different novel ternary additives, ZrN-AlN-Al2O3/Y2O3, and spark plasma sintering at 1550 degrees C under 40 MPa. The phase composition, microstructure, grain distribution, crack propagation process and mechanical properties of sintered bulk were investigated. Results demonstrated that the sintered alpha/beta-Si3N4 composite ceramics with ZrN-AlN-Al2O3 contained the most alpha phase, which resulted in a maximum Vickers hardness of 18.41 +/- 0.31 GPa. In the alpha/beta-Si3N4 composite ceramics with ZrN-AlN-Y2O3 additives, Zr3AlN MAX-phase and ZrO phase were found and their formation mechanisms were explained. The fracture appearance presented coarser elongated beta-Si3N4 grains and denser microstructure when 20 wt% TiC particles were mixed into Si3N4 matrix, meanwhile, exhibited maximum mean grain diameter of 0.98 +/- 0.24 mu m. As a result, the compact alpha/beta-Si3N4 composite ceramics containing ZrN-AlN-Y2O3 additives and TiC particles displayed the optimal bending strength and fracture toughness of 822.63 +/- 28.75 MPa and 8.53 +/- 0.21 MPa.m(1/2), respectively. Moreover, the synergistic toughening of rod-like beta-Si3N4 grains and TiC reinforced particles revealed the beneficial effect on the enhanced fracture toughness of Si3N4 ceramic matrix.

Automated summary

In this study, high hardness and toughness alpha/beta-Si3N4 composite ceramics were fabricated using novel ternary additives and spark plasma sintering. The composition, microstructure, grain distribution, crack propagation process, and mechanical properties of the ceramics were investigated. The results demonstrated the influence of different additives on the phase composition and mechanical properties of the ceramics. The addition of ZrN-AlN-Al2O3 resulted in the highest hardness, while the addition of ZrN-AlN-Y2O3 and TiC particles improved the bending strength and fracture toughness of the ceramics.