Preparation and Properties of Machinable Si₂N₂O/BN Composites

Abstract

Si 2 N 2 O/BN composites were successfully fabricated. With increasing BN content, the elastic modulus and hardness almost linearly decrease while the flexural strength does not exhibit a dramatic degradation. This is attributed to the fact that the homogeneously dispersed nanosized BN particles inhibit the grain growth of Si 2 N 2 O. The critical thermal-shock resistance temperature of the Si 2 N 2 O/30 vol% BN composite is enhanced by 4001C than monolithic Si 2 N 2 O. The introduction of BN significantly improves the dielectric properties and machinability. The Si 2 N 2 O/BN composites show a combination of high strength, low dielectric constant, good thermal shock resistance, and machinability, indicating that they are promising structural/functional materials.

Thermal shock resistance of the porous boron nitride/silicon oxynitride ceramic composites

“…In addition, during the oxidation in the process of thermal shock tests, the vitreous phase viscosity on the surface of samples was reduced by the outward diffusion of Li ions in the intergranular phase . The vitreous phase can heal the surface flaws caused by machining, thereby improving the flexural strength of the as‐quenched samples . The surface dense oxide layer can act as an additional thermal barrier that can reduce heat transfer coefficient.…”

Fabrication and properties of porous boron nitride/silicon oxynitride ceramic composites via gas pressure sintering

“…Tong reported that dense BN/Si 2 N 2 O composite prepared by hot pressing technique could withstand a thermal shock of 1000°C [7]. Since porous ceramics were reported to have better thermal shock resistance [15,[18][19][20], porous BN/Si 2 N 2 O ceramic composites may exhibit a better resistance than the dense bodies.…”

“…Pure and dense Si 2 N 2 O ceramic obtained by hot pressing technique exhibited good mechanical and dielectric properties, thus making it a potential wave transparent material [6,7]. However, the as-sintered dense bodies showed poor thermal shock resistance (critical temperature difference ΔT c = 600°C), and the dielectric constant (ε = 6.17) is still too high for use in broadband missile antenna shield [8][9][10].…”

Fabrication and Characterization of In Situ Porous Si3N4‐Si2N2O‐BN Ceramic

“…Si 2 N 2 O is the unique compound in the Si 3 N 4 ‐SiO 2 quasi‐binary system . Like Si 3 N 4 , Si 2 N 2 O also shows excellent performance especially the enhanced oxidation resistance and wave transmission properties for high‐temperature wave‐transparent uses . It has been found that Si 3 N 4 /Si 2 N 2 O ceramic has a modified microstructure that combines the favorable properties such as the strength of Si 3 N 4 and the oxidation resistance of Si 2 N 2 O .…”

“…Si 2 N 2 O ceramics are generally fabricated by reactive sintering of the mixture of Si 3 N 4 and SiO 2 in the presence of liquid phase obtained by the addition of M x O y ( M = Al, Y, Li, et al .) . During the sintering process, liquid phase forms as a result of reactions between all constituents above the eutectic temperature and promotes the densification and formation of Si 2 N 2 O .…”