Microstructure and mechanical properties of three porous Si3N4 ceramics fabricated by different techniques

Three porous Si3N4 ceramics were fabricated using the same starting Si3N4 powder by techniques of (1) oxidation-bonding combined with sol–gel infiltration sintering (OB-IS), (2) cold-pressing combined with pressureless-sintering (CP-PS), and (3) 3D-printing combined with pressureless-sintering (3DP-PS). Due to the obvious difference in microstructure, phase composition, linear shrinkage, pore size distribution and porosity, the three porous Si3N4 ceramics possess characteristic in mechanical properties. Si3N4-(OB-IS) possesses lower flexural strength (23–120 MPa), fracture toughness (0.4–1.4 MPa m1/2) and Young's modulus (9.1–26.3 GPa) but the highest Vickers hardness (1.1–4.1 GPa). Si3N4-(CP-PS) possesses the highest flexural strength (143–207 MPa), fracture toughness (2.3–3.4 MPa m1/2) and Young's modulus (45.8–58.5 GPa) but lower Vickers hardness (0.8–1.1 GPa). Si3N4-(3DP-PS) possesses the lowest flexural strength (13 MPa), fracture toughness (0.3 MPa m1/2), Young's modulus (3.9 GPa) and Vickers hardness (0.4 GPa).

► We fabricated three porous Si3N4 ceramics using the same starting Si3N4 powder by different techniques.
► We discussed in detail the reasons causing the difference in mechanical property of the three porous Si3N4 ceramics.
► Si3N4-(OB-IS) has the highest Vickers hardness due to its low porosity.
► Si3N4-(CP-PS) has the highest flexural strength and fracture toughness due to the good bearing capacity of β-Si3N4 grains.