New route to improve the fracture toughness and flexural strength of Si3N4 ceramics by adding FeSi2

Silicon nitride (Si3N4) ceramics were pressureless sintered with 0.2 wt% FeSi2 at 1780 °C for 2 h in nitrogen with Al2O3 and Y2O3 as sintering aids and found to have high toughness and strength. During the sintering process, β-Si3N4 crystal seeds and Fe5Si3 reinforcing particles were in situ generated by FeSi2. Abnormal growth of Si3N4 grains was promoted by β-Si3N4 crystal seeds. High thermal expansion coefficient of Fe5Si3 particles induced residual stresses in the ceramics matrix, which deflected the crack. Ultimately, the fracture toughness and flexural strength of Si3N4 ceramics reached 9.8 ± 0.5 MPa·m1/2 and 1086 ± 48 MPa respectively.