Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infilt...Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infiltration (CVI). The composition and microstructure of the SiC/PyC materials were investigated in detail by XRD, SEM and EDS, etc. The effects of the deposition temperature on the section features and wear resistance of the SiC/PyC were studied. The results show that the PyC layers were deposited onto SiC substrates spontaneously at a lower deposition temperature. The SiC substrates deposited with PyC can significantly reduce the wear rate of the self-dual composite materials under dry sliding condition. The wear tests suggest that the SiC/PyC composite materials own a better wear resistance property when the deposition temperature is 800 °C, and the wear rate is about 64.6% of that without the deposition of PyC.展开更多
Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s...Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s.Pyrolysis carbon(PyC)“bridges”were constructed between SiC particles through the carbonisation of phenolic resin,providing a large number of current channels.The incubation time of the flash sintering process was significantly reduced,and the sintering difference between the centre and the edge regions of the ceramics was minimized,with an average particle size of the centre region and edge region being 12.31 and 9.02μm,respectively.The results showed that the porosity of the SiC ceramics after the flash sintering was reduced to 14.79% with PyC“bridges”introduced,and the Vickers hardness reached 19.62 GPa.PyC“bridges”gradually evolved from amorphous eddy current carbon to oriented graphite carbon,indicating that the ultra-high temperature environment in which the sample was located during the flash sintering was successfully constructed.Ultra-high temperature flash sintering of SiC is expected to be applied to the local repair of matrix damage in SiC ceramic matrix composites.展开更多
Aiming to obtain microwave absorbing materials with excellent mechanical and microwave absorption properties, carbon fiber reinforced Si3N4 ceramics(Cf-Si3N4) with pyrolytic carbon(PyC)/SiC interphases were fabricated...Aiming to obtain microwave absorbing materials with excellent mechanical and microwave absorption properties, carbon fiber reinforced Si3N4 ceramics(Cf-Si3N4) with pyrolytic carbon(PyC)/SiC interphases were fabricated by gel casting. The influences of carbon fibers content on mechanical and microwave absorption properties of as-prepared Si3N4 based ceramics were investigated. Results show that chemical compatibility between carbon fibers and Si3N4 matrix in high temperature environment can be significantly improved after introduction of Py C/SiC interphases. As carbon fibers content increases from 0 to 4 wt%, flexural strength of Si3N4 based ceramics decreases slightly while fracture toughness obviously increases. Moreover, both the real and imaginary parts of complex permittivity increase with the rising of carbon fibers content within the frequency range of 8.2–12.4 GHz. Investigation of microwave absorption shows that the microwave attenuation ability of Cf-Si3N4 ceramics with Py C/SiC interphases is remarkably enhanced compared with pure Si3N4 ceramics. Effective absorption bandwidth(<-10 d B) of10.17–12.4 GHz and the minimum reflection less of-19.6 d B are obtained for Si3N4 ceramics with 4 wt%carbon fibers in 2.0 mm thickness. Cf-Si3N4 ceramics with Py C/SiC interphases are promising candidates for microwave absorbing materials with favorable mechanical property.展开更多
SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the c...SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.展开更多
Pyrolytic carbon （PyC） was infiltrated into silicon nitride （Si3N4） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the...Pyrolytic carbon （PyC） was infiltrated into silicon nitride （Si3N4） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si3N4-PyC composite ceramics. Dielectric permittivity, electromagnetic interference （EMI） shielding and absorption properties of Si3N4-PyC composite ceramics were studied as a function of Ni content at 8.2-12.4 GHz （X-band）. When Ni nanoparticles were added into phenolic resin, the electric conductivity of the prepared composite ceramics decreased with increasing Ni content, which was attributed to the decrease of graphitization degree of PyC. The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness. Since too high permittivity is harmful to the impendence match and results in the strong reflection, the electromagnetic wave absorption property of Si3N4-PyC composite ceramics increases with increasing Ni content. When the content of Ni nanoparticles added into phenolic resin was 2 wt%, the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.展开更多
基金Project(2011CB605801)supported by the National Basic Research Program of ChinaProject(2011M500127)supported by the China Postdoctoral Science Foundation+2 种基金Projects(51102089,50802115)supported by the National Natural Science Foundation of ChinaProjects(12JJ4046,12JJ9014)supported by the Natural Science Foundation of Hunan Province,ChinaProject(74341015817)supported by the Post-doctoral Fund of Central South University,China
文摘Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infiltration (CVI). The composition and microstructure of the SiC/PyC materials were investigated in detail by XRD, SEM and EDS, etc. The effects of the deposition temperature on the section features and wear resistance of the SiC/PyC were studied. The results show that the PyC layers were deposited onto SiC substrates spontaneously at a lower deposition temperature. The SiC substrates deposited with PyC can significantly reduce the wear rate of the self-dual composite materials under dry sliding condition. The wear tests suggest that the SiC/PyC composite materials own a better wear resistance property when the deposition temperature is 800 °C, and the wear rate is about 64.6% of that without the deposition of PyC.
基金supported by the National Natural Science Foundation of China(No.92160202)the National Natural Science Foundation of China(No.52375188)+1 种基金the National Key R&D Program of China(No.2021YFB3703100)the Ningbo Key Technology Research and Development(No.2023T007).
文摘Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s.Pyrolysis carbon(PyC)“bridges”were constructed between SiC particles through the carbonisation of phenolic resin,providing a large number of current channels.The incubation time of the flash sintering process was significantly reduced,and the sintering difference between the centre and the edge regions of the ceramics was minimized,with an average particle size of the centre region and edge region being 12.31 and 9.02μm,respectively.The results showed that the porosity of the SiC ceramics after the flash sintering was reduced to 14.79% with PyC“bridges”introduced,and the Vickers hardness reached 19.62 GPa.PyC“bridges”gradually evolved from amorphous eddy current carbon to oriented graphite carbon,indicating that the ultra-high temperature environment in which the sample was located during the flash sintering was successfully constructed.Ultra-high temperature flash sintering of SiC is expected to be applied to the local repair of matrix damage in SiC ceramic matrix composites.
基金National High-Tech Research and Development Program of China(2013AA8011004B)Foundation for Innovative Research Groups of the National Natural Science Foundation of China(CX201227)State Key Laboratory of Solidification Processing in NWPU(SKLSP201103)
基金supported by the National Natural Science Foundation of China (Grant No. 51604107)the Natural Science Foundation of Hunan Province (Grant No. 2019JJ50115 and 2019JJ50768)
文摘Aiming to obtain microwave absorbing materials with excellent mechanical and microwave absorption properties, carbon fiber reinforced Si3N4 ceramics(Cf-Si3N4) with pyrolytic carbon(PyC)/SiC interphases were fabricated by gel casting. The influences of carbon fibers content on mechanical and microwave absorption properties of as-prepared Si3N4 based ceramics were investigated. Results show that chemical compatibility between carbon fibers and Si3N4 matrix in high temperature environment can be significantly improved after introduction of Py C/SiC interphases. As carbon fibers content increases from 0 to 4 wt%, flexural strength of Si3N4 based ceramics decreases slightly while fracture toughness obviously increases. Moreover, both the real and imaginary parts of complex permittivity increase with the rising of carbon fibers content within the frequency range of 8.2–12.4 GHz. Investigation of microwave absorption shows that the microwave attenuation ability of Cf-Si3N4 ceramics with Py C/SiC interphases is remarkably enhanced compared with pure Si3N4 ceramics. Effective absorption bandwidth(<-10 d B) of10.17–12.4 GHz and the minimum reflection less of-19.6 d B are obtained for Si3N4 ceramics with 4 wt%carbon fibers in 2.0 mm thickness. Cf-Si3N4 ceramics with Py C/SiC interphases are promising candidates for microwave absorbing materials with favorable mechanical property.
基金financial support of the project from the National Natural Science Foundation of China(No.51821091 and 51872233)the Research Foundation of Chengdu University of Technology(No.10912-KYQD202008264)。
文摘SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.
基金supported by the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China(No.KB200920)the Natural Science Foundation of China(No.50972119)the Programme of Introducing Talents of Discipline to Universities, China(No.B08040)
文摘Pyrolytic carbon （PyC） was infiltrated into silicon nitride （Si3N4） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si3N4-PyC composite ceramics. Dielectric permittivity, electromagnetic interference （EMI） shielding and absorption properties of Si3N4-PyC composite ceramics were studied as a function of Ni content at 8.2-12.4 GHz （X-band）. When Ni nanoparticles were added into phenolic resin, the electric conductivity of the prepared composite ceramics decreased with increasing Ni content, which was attributed to the decrease of graphitization degree of PyC. The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness. Since too high permittivity is harmful to the impendence match and results in the strong reflection, the electromagnetic wave absorption property of Si3N4-PyC composite ceramics increases with increasing Ni content. When the content of Ni nanoparticles added into phenolic resin was 2 wt%, the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.
