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 (23-120MPa), fracture toughness (0.4-1.4MPam^1/2) and Young's modulus (9.1-26.3GPa) but the highest Vickers hardness (1.1-4.1GPa). Si₃N₄-(CP-PS) possesses the highest flexural strength (143-207MPa), fracture toughness (2.3-3.4MPam^1/2) and Young's modulus (45.8-58.5GPa) but lower Vickers hardness (0.8-1.1GPa). Si₃N₄-(3DP-PS) possesses the lowest flexural strength (13MPa), fracture toughness (0.3MPam^1/2), Young's modulus (3.9GPa) and Vickers hardness (0.4GPa).