Effect of Porosity and Microstructure on the Strength of Si₃N₄: Designed Microstructure for High Strength, High Thermal Shock Resistance, and Facile Machining

Abstract

The flexural strength of porous Si 3 N 4 ceramics with a variety of microstructures and porosities were evaluated, and the effect of microstructure on the flexural strength was investigated to obtain machinable Si 3 N 4 ceramics having both high strength and high thermal shock resistance. Porous Si 3 N 4 having three types of microstructure, consisting of (1) only spherical grains, (2) combinations of spherical and columnar grains, and (3) only columnar ␤-grains connected randomly in three dimensions, were readied as specimens. Their mean pore diameters and porosities were 0.2 to 0.3 µm and 8% to 59%, respectively. The flexural strength of the porous Si 3 N 4 (3) was much larger than that of the porous Si 3 N 4 having the other microstructures, and the maximum flexural strength was 455 MPa at a porosity of 38.3%. The thermal shock resistance (⌬T), which was determined by a water quench test, of porous Si 3 N 4 with such microstructure and a porosity of 50% was 980 K. All of the porous Si 3 N 4 (3) was easily machined with cemented carbide drills.

Characterization of porous silicon nitride/silicon oxynitride composite ceramics produced by sol infiltration

“…Porous ceramics with a tailored microstructure are promising high-performance materials because of such unique properties as light weight, good strain tolerance, damage tolerance and thermal shock resistance [5,6]. In general, porous Si 3 N 4 /Si 2 N 2 O ceramics have been used as hot gas filters and catalyst supports [7].…”

Properties of Si3N4 Ceramics Sintered in Air and Nitrogen Atmosphere Furnaces

“…4 We conclude that sintering of Si 3 N 4 ceramics in air atmosphere furnace can not compete with the conventional sintering technology, using N 2 gas furnace, as the properties of specimens are not as good as those sintered in N 2 atmosphere. Moreover, the quality of the sintered specimen may inconsistent due to the oxidized layer generated by sintering in the air.…”

Microstructure and Properties of Porous Si3N4/Dense Si3N4 Joints Bonded Using RE–Si–Al–O–N (RE = Y or Yb) Glasses

“…The porous Si 3 N 4 (P-Si 3 N 4 ) ceramics are emphasized for some engineering applications such as catalyst supports and gas filters due to its high mechanical strength, low dielectric constant, low density, and porous nature [5][6][7][8]. In the present work, the porous Si 3 N 4 ceramics were tried to join to the dense Si 3 N 4 to combine the performance advantages of both the materials.…”