Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the ...Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented展开更多
The sintering additives such as Al2O3 and/or Y2O3 were coated on the surfaces of Si3N4 particles via heterogeneous nucleation processing using a buffered pH solution as the precipitation reagent. They nucleated and gr...The sintering additives such as Al2O3 and/or Y2O3 were coated on the surfaces of Si3N4 particles via heterogeneous nucleation processing using a buffered pH solution as the precipitation reagent. They nucleated and grew only on the surfaces of Si3N4 and did not form sol particles in solution by TEM observation. The isoelectric point (IEP) of coated Si3N4 was different from that of as-received Si3N4. The IEP of AI(OH)3-coated Si3N4 occurred at pH8.4, which is close to that of alumina. When AI(OH)3-coated Si3N4 particles were coated with Y(OH)3, the IEP of coated Si3N4 powder shifted from pH8.4 to pH9.2, similar to that of yttria. In addition, the rheological data showed that Al2O3 and/or Y2O3 coated Si3N4 suspension is nearly Newtonian and that added Si3N4 suspension shows a shear rate thinning behavior.展开更多
The effect of rare earth oxides Y 2O 3 or CeO 2 on sintering properties of Si 3N 4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results indicate that the best sint...The effect of rare earth oxides Y 2O 3 or CeO 2 on sintering properties of Si 3N 4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results indicate that the best sintering properties appear in Si 3N 4 ceramics with 5% Y 2O 3 or 8% CeO 2. Secondary crystallites are formed at grain boundaries after heat treatment, which decreases the amount of glass phase and contributes to the improvement of high temperature mechanical properties of silicon nitride.展开更多
Porous Si3N4–Si3N4 composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration(CVI).This technique could effectively improve the designability of porous Si3N4 ceramics and...Porous Si3N4–Si3N4 composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration(CVI).This technique could effectively improve the designability of porous Si3N4 ceramics and optimize the mechanical and dielectric properties.The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si3N4–Si3N4 composite ceramics were studied.The study highlights following:When CVI processing time was increased from 0 to 12 h,the porosity decreased from68.65%to 26.07%and the density increased from 0.99 to 2.02 g/cm3.At the same time,the dielectric constant gradually increased from 1.72 to 3.60;however,the dielectric loss always remained less than0.01,indicating the excellent electromagnetic(EM)wave-transparent performance of porous Si3N4–Si3N4 composite ceramics.The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h.After heat treatment,the porosity increased from 26.07%to 36.02%and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01.It has been demonstrated that the porous Si3N4–Si3N4 composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.展开更多
文摘Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented
文摘The sintering additives such as Al2O3 and/or Y2O3 were coated on the surfaces of Si3N4 particles via heterogeneous nucleation processing using a buffered pH solution as the precipitation reagent. They nucleated and grew only on the surfaces of Si3N4 and did not form sol particles in solution by TEM observation. The isoelectric point (IEP) of coated Si3N4 was different from that of as-received Si3N4. The IEP of AI(OH)3-coated Si3N4 occurred at pH8.4, which is close to that of alumina. When AI(OH)3-coated Si3N4 particles were coated with Y(OH)3, the IEP of coated Si3N4 powder shifted from pH8.4 to pH9.2, similar to that of yttria. In addition, the rheological data showed that Al2O3 and/or Y2O3 coated Si3N4 suspension is nearly Newtonian and that added Si3N4 suspension shows a shear rate thinning behavior.
文摘The effect of rare earth oxides Y 2O 3 or CeO 2 on sintering properties of Si 3N 4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results indicate that the best sintering properties appear in Si 3N 4 ceramics with 5% Y 2O 3 or 8% CeO 2. Secondary crystallites are formed at grain boundaries after heat treatment, which decreases the amount of glass phase and contributes to the improvement of high temperature mechanical properties of silicon nitride.
基金supported by the Chinese National Foundation for Natural Sciences under Contract (Nos. 51602258 and 51672217)111 Project of China (B08040)
文摘Porous Si3N4–Si3N4 composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration(CVI).This technique could effectively improve the designability of porous Si3N4 ceramics and optimize the mechanical and dielectric properties.The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si3N4–Si3N4 composite ceramics were studied.The study highlights following:When CVI processing time was increased from 0 to 12 h,the porosity decreased from68.65%to 26.07%and the density increased from 0.99 to 2.02 g/cm3.At the same time,the dielectric constant gradually increased from 1.72 to 3.60;however,the dielectric loss always remained less than0.01,indicating the excellent electromagnetic(EM)wave-transparent performance of porous Si3N4–Si3N4 composite ceramics.The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h.After heat treatment,the porosity increased from 26.07%to 36.02%and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01.It has been demonstrated that the porous Si3N4–Si3N4 composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.
