C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high...C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment（HTT） at the break of CVI process.According to the load？displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load？displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.展开更多
C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/...C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C-SiC and C/C-ZrC-SiC composites exhibited good ablation resistance under the plasma flame above 2300℃. Withtheincreaseof ZrC content, a continuous oxide layer and a solid Zr-Si-O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC-SiC ceramics. The solid ZrO2-ZrC and Zr-Si-O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2-ZrO2-ZrC-SiC layer would serve as a thermal and oxygen barrier for preventing the substratefrom further ablation. The C/C-ZrC-SiC composites with 27.2%ZrC and 7.56%SiC shows superior ablation resistance, and the mass and linear ablation rates are-3.51 mg/s and-1.88 μm/s, respectively.展开更多
Phosphate-coating was prepared for C/C composite using liquid-impregnation and different heat-treatment. The results show that the mass-loss rate of sample A with 1-2 ℃/min slow-cooling rate technology is 47%after ox...Phosphate-coating was prepared for C/C composite using liquid-impregnation and different heat-treatment. The results show that the mass-loss rate of sample A with 1-2 ℃/min slow-cooling rate technology is 47%after oxidation at 700 ℃ for 20 h, while that of sample B with air-fast-cooling one is only 0.98%. SEM images reveal that the coating of sample A is full of micro-holes, micro-cracks and many piece-like crystal particles, while that of sample B is integrated and compacted in glassy state with a few of micro-cracks. The coating of sample A is almost exhausted only in 8 h oxidized-test at 700 ℃, while that of sample B remains integrated after 8 h test at 700 ℃ and becomes loose due to much small pores generated after 20 h test at 700 ℃.展开更多
A SiC/ZrSiO4？SiO2 （SZS） coating was successfully fabricated on the carbon/carbon （C/C） composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock r...A SiC/ZrSiO4？SiO2 （SZS） coating was successfully fabricated on the carbon/carbon （C/C） composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock resistance. The anti-oxidation properties under different oxygen partial pressures （OPP） and thermal shock resistance of the SZS coating were investigated. The results show that the SZS coated sample under low OPP, corresponding to the ambient air, during isothermal oxidation was 0.54% in mass gain after 111 h oxidation at 1500 ° C and less than 0.03% in mass loss after 50 h oxidation in high OPP, corresponding to the air flow rate of 36 L/h. Additionally, the residual compressive strengths （RCS） of the SZS coated samples after oxidation for 50 h in high OPP and 80 h in low OPP remain about 70% and 72.5% of those of original C/C samples, respectively. Moreover, the mass loss of SZS coated samples subjected to the thermal cycle from 1500 ° C in high OPP to boiling water for 30 times was merely 1.61%.展开更多
SiC nanowires were prepared on C/C composite surface without catalyst by chemical vapor deposition（CVD） using CH3 SiCl3 as precursor.SEM images of the CVD-product reveal that some long nanowires have grown to tens o...SiC nanowires were prepared on C/C composite surface without catalyst by chemical vapor deposition（CVD） using CH3 SiCl3 as precursor.SEM images of the CVD-product reveal that some long nanowires have grown to tens of micrometers with some gathered as a ball.Some short nanowires agglomerate like chestnut shell with many thorns accompanied by some deposited nano-particles.XRD,Raman-spectrum and FTIR patterns indicate that the product is a typical β-SiC.TEM images show that the nanowires have a wide diameter range from 10 to 100 nm,and some thin nanowires are bonded to the thick one by amorphous CVD-SiC.A SiC branch generates from an amorphous section of a thick one with an angle of 70° between them,which is consistent with the [111] axis stacking angle of the crystal.SAED and fast Fourier transform（FFT） patterns reveal that the nanowires can grow along with different axes,and the bamboo-nodes section is full of stacking faults and twin crystal.The twisted SiC lattice planes reveal that the screw dislocation growth is the main mechanism for the CVD-SiC nanowires.展开更多
Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C com...Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.展开更多
Using natural gas as carbon source, 2D needle felt as preform, 2D-C/C composites were prepared by thermal gradient chemical vapor infiltration. Their microstructures were observed under polarized light microscope （PL...Using natural gas as carbon source, 2D needle felt as preform, 2D-C/C composites were prepared by thermal gradient chemical vapor infiltration. Their microstructures were observed under polarized light microscope （PLM） and scanning electron microscope （SEM）, and the flexural behaviors before and after heat-treatment were studied with a universal mechanical testing machine. The fracture mechanism of the composites was discussed in detail. The results show that, carbon matrix exhibits pure smooth laminar （SL） characteristic including numerous wrinkled layered structures and some inter-laminar micro-cracks. With the decreasing density, the strength of the composites decreases and the toughness increases slightly; after 2500 °C heat-treatment, the inter-laminar micro-cracks in matrix increase, the strength decreases, and the toughness obviously increases. The fracture mode of the composites changes from brittle to pseudo-plastic characteristic due to more crack deflections in SL matrix.展开更多
A seal device as an important component of aeroengines has decisive influence on per-formance,reliability,and working life of aeroengines.With the development of aeroengines,demands on the performance characteristics ...A seal device as an important component of aeroengines has decisive influence on per-formance,reliability,and working life of aeroengines.With the development of aeroengines,demands on the performance characteristics of seal devices are made strictly.Finger seal as a novel kind of sealing device,recently attracts more and more attentions in academic circles and engineer-ing fields at home and abroad.Research on finger seals has been extensively developed,especially on leakage and wear performances under dynamic conditions.However,it is a pity that the work on finger seals has been limited with a single approach that is improving the performance by structural optimization;in addition,the technology of dynamic analysis on finger seals is weak.Aiming at the problems mentioned above,a distributed mass equivalent dynamic model of finger seals considering the coupling effect of overlaid laminates is established in the present paper,the dynamic perfor-mance of 2.5 dimension C/C composite finger seal is analyzed with the model,and then the effects of fiber bundle density and fiber bundle preparation direction on finger seal's dynamic performance are discussed,as well as compared with those of Co-based alloy finger seal.The current work is about dynamic analysis of finger seals and application of C/C composite in this paper may have much academic significance and many engineering values for improving research level of finger seal dynamics and exploring feasibility of C/C composite being used for finger seals.展开更多
Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by ...Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.展开更多
To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the ya...To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the yam unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 ~C. The deviation between the simulated and exl^erimental axial CTE of 3D braided C/C composites is no more than 11%. The effects of different parameters （including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson＇s ratio and CTEs of carbon fibers and carbon matrix） were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson＇s ratio of carbon matrix.展开更多
A(ZrC/SiC)_(3)alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical vapor deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m^2.The resu...A(ZrC/SiC)_(3)alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical vapor deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m^2.The results indicated that the alternate coating exhibited great ablation resistance,providing an effective protection for C/C composites.In initial rapid heating stage,the(ZrC/SiC)_(3) alternate coating can relieve thermal stress,avoiding the peeling of coating and keeping an intact coating structure.In subsequent ablation,the Si C layers in central region were consumed rapidly,leaving layered interspaces.Three stacked ZrO_(2) layers were reserved with the assistance of the release of thermal stress by interspaces,offering a great anti-scouring effect.In transition and border regions,the alternate Si C layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO_(2).It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.展开更多
Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, bu...Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast pre- diction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces＂ coefficients of 2.5D CC com- posites are evaluated using multiple linear regression method. Verification experiment has been car- ried out through a group of orthogonal tests. Results indicate that the proposed nmdel is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.展开更多
The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0&#...The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0°/45° weftless fabric lay-up and 0°/45° twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0°/45° weftless composite has a fiat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0°/90° weftless and the 0°/45° twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect （oxidation）, and a little by the thermo-mechanical effect （mechanical denudation）. The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.展开更多
A new method for preparation of TaC coating on C/C composite material is reported.The amorphous ethylate tantalum jellied as the precursor is prepared and spread densely on the surface of the C/C composite material so...A new method for preparation of TaC coating on C/C composite material is reported.The amorphous ethylate tantalum jellied as the precursor is prepared and spread densely on the surface of the C/C composite material so as to form a multilayer film.In a graphitization furnace the multilayer film is transformed into TaC coating at various temperatures.Ethylate tantalum film is characterized by FT-IR(Fourier transform infrared)spectra,XRD(X-ray diffraction)and SEM(scanning electron microscopy)and TaC coating is characterized by XRD and SEM.At 1200℃the coating contained TaC and Ta2O5,and at above 1400℃only TaC is formed.The coating formed at 1600℃is a continuous stratum structure,and that formed at 1600℃is a porous net structure.Analysis on thermodynamics and formation mechanism of TaC indicates that,after ethylate tantalum is decomposed,Ta2O5 is first produced and then transformed into Ta2C,and newly formed Ta2C is transformed into TaC by the sufficient C at last.展开更多
The precise microscopic feature of carbon-carbon（C/C） composites is essential {or an accurate predic tion of their mechanical behavior. After fabrication, actual microscopic feature differs from simple ideal spatial...The precise microscopic feature of carbon-carbon（C/C） composites is essential {or an accurate predic tion of their mechanical behavior. After fabrication, actual microscopic feature differs from simple ideal spatial model. Micro computed lomography（CT） scan can well describe internal microstruetures of composites. Therefore, a reconstructed model is developed based on mireo-CT, by a series of prodcedures including extrac tlng components, generating new binary images and establishing a finite element （FE） model. Compared with the model designed by reconstructed commercial software MIMICS. the presented reconstructed FE model is superior in terms of high mesh quality and eontrollable mesh cluantity. The precision of the model is verified by experiment.展开更多
The novel Ni-based brazing filler was used to join C/C composites.When brazing temperature increased from 1080 to 1100°C,the wetting angle decreased from 23°to 14°,and the brazing filler had good wettab...The novel Ni-based brazing filler was used to join C/C composites.When brazing temperature increased from 1080 to 1100°C,the wetting angle decreased from 23°to 14°,and the brazing filler had good wettability on the surface of C/C composites.The brazing seam of the brazed joint consisted of Ni(s,s)and Cr_(3)C_(2) phases.As brazing temperature increased,lots of Cr_(3)C_(2) phases were generated at the bonding interface,and the thick reaction layer was formed.When brazing temperature was 1120°C,the shear strength of C/C joint reached the maximum value of 31.5 MPa.The fracture path extended in the C/C matrix close to the bonding interface.展开更多
In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase com...In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
The C/C composite brake discs were prepared by tri-cylindrical chemical vapor deposition （CVD） process. The optimum processing parameters were as follows： deposition temperature was 830 - 930 ℃, the gas- flow rate...The C/C composite brake discs were prepared by tri-cylindrical chemical vapor deposition （CVD） process. The optimum processing parameters were as follows： deposition temperature was 830 - 930 ℃, the gas- flow rates of N2 and propylene were 4.8 - 5.2 m^3/h and 5.8 - 6.2 m^3/h, respectively, the furnace pressure was 4.5 - 5.5 kPa and the deposition time was 200 h. The effects of processing parameters on the densified rates, thermal-physical property and mechanical performance of C/C composite brake discs were studied. The results show that density, heat conductivity, bend strength and abrasion ratio of the multi-cylindrica brake discs are 1. 02 - 1. 78 g/cm^3 , 31 W/（m·K）, 114 MPa and 7μm/s, respectively, which are approximately similar to those of the singlecylindrical ones. The gas tlow rate has no relation to the number of the cylinder and furnace loading. The utilization ratio of carbon can be improved by multi-cylinder CVD process without changing the characteristics of brake disc.展开更多
2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. Th...2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.展开更多
Hexagonal boron nitride(h-BN)powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration(CVI)for densification to prepare carbon fiber reinforced/carbo...Hexagonal boron nitride(h-BN)powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration(CVI)for densification to prepare carbon fiber reinforced/carbon and boron nitride dual matrix composites(C/C-BN).Microstructures and mechanical properties of C/C composites with three different volume contents of h-BN powders were investigated in comparison to pure C/C composites.Results indicated that the introduction of h-BN powders into C/C composites significantly reduced the size of Py C and the anisotropy of thermal contraction in matrix,leading to a gradual disappearance of ring defects as the h-BN content increased.In addition,an enhanced interfacial bonding between fiber and matrix obtained due to higher-textured Py C and rougher fiber surface.Thereby,the flexural strengths and modulus of as-prepared composites decreased firstly and then increased,while the impact toughness presented a decreasing tendency as the content of BN powders increased.Furthermore,with the increasing of h-BN content,anisotropies of compressive properties were weakened,and the compressive strength of C/C-BN composites were always higher than that of pure C/C composit.However,when C/C composites modified by 13.5 vol%content of h-BN,excessive loose BN aggregates appeared in C/C-BN composites,leading to a relatively slight reduction of compressive strength.展开更多
基金Project (50802115) supported by the National Natural Science Foundation of ChinaProject (2011CB605801) supported by the National Basic Research Program of China
文摘C/C composites with banded structure pyrocarbon were fabricated by fast chemical vapor infiltration（CVI）,with C3H6 as carbon source,N2 as carrier gas,and three-dimensional（3D） 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment（HTT） at the break of CVI process.According to the load？displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load？displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.
基金Project(2011CB605801)supported by the National Basic Research Program of ChinaProject(51304249)supported by the National Natural Science Foundation of China+1 种基金Project(2013BAE04B02)supported by the National Key Technology Support Program of ChinaProject(14JJ3023)supported by the Hunan Provincial Science Foundation of China
文摘C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C-SiC and C/C-ZrC-SiC composites exhibited good ablation resistance under the plasma flame above 2300℃. Withtheincreaseof ZrC content, a continuous oxide layer and a solid Zr-Si-O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC-SiC ceramics. The solid ZrO2-ZrC and Zr-Si-O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2-ZrO2-ZrC-SiC layer would serve as a thermal and oxygen barrier for preventing the substratefrom further ablation. The C/C-ZrC-SiC composites with 27.2%ZrC and 7.56%SiC shows superior ablation resistance, and the mass and linear ablation rates are-3.51 mg/s and-1.88 μm/s, respectively.
基金Projects(09JJ4027)supported by the Natural Science Foundation of Hunan Province,ChinaProject(201206375003)supported by China Scholarship Council
文摘Phosphate-coating was prepared for C/C composite using liquid-impregnation and different heat-treatment. The results show that the mass-loss rate of sample A with 1-2 ℃/min slow-cooling rate technology is 47%after oxidation at 700 ℃ for 20 h, while that of sample B with air-fast-cooling one is only 0.98%. SEM images reveal that the coating of sample A is full of micro-holes, micro-cracks and many piece-like crystal particles, while that of sample B is integrated and compacted in glassy state with a few of micro-cracks. The coating of sample A is almost exhausted only in 8 h oxidized-test at 700 ℃, while that of sample B remains integrated after 8 h test at 700 ℃ and becomes loose due to much small pores generated after 20 h test at 700 ℃.
基金Project supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,ChinaProject(51205417)supported by the National Natural Science Foundation of China
文摘A SiC/ZrSiO4？SiO2 （SZS） coating was successfully fabricated on the carbon/carbon （C/C） composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock resistance. The anti-oxidation properties under different oxygen partial pressures （OPP） and thermal shock resistance of the SZS coating were investigated. The results show that the SZS coated sample under low OPP, corresponding to the ambient air, during isothermal oxidation was 0.54% in mass gain after 111 h oxidation at 1500 ° C and less than 0.03% in mass loss after 50 h oxidation in high OPP, corresponding to the air flow rate of 36 L/h. Additionally, the residual compressive strengths （RCS） of the SZS coated samples after oxidation for 50 h in high OPP and 80 h in low OPP remain about 70% and 72.5% of those of original C/C samples, respectively. Moreover, the mass loss of SZS coated samples subjected to the thermal cycle from 1500 ° C in high OPP to boiling water for 30 times was merely 1.61%.
基金Project(201206375003)supported by the China Scholarship Council
文摘SiC nanowires were prepared on C/C composite surface without catalyst by chemical vapor deposition（CVD） using CH3 SiCl3 as precursor.SEM images of the CVD-product reveal that some long nanowires have grown to tens of micrometers with some gathered as a ball.Some short nanowires agglomerate like chestnut shell with many thorns accompanied by some deposited nano-particles.XRD,Raman-spectrum and FTIR patterns indicate that the product is a typical β-SiC.TEM images show that the nanowires have a wide diameter range from 10 to 100 nm,and some thin nanowires are bonded to the thick one by amorphous CVD-SiC.A SiC branch generates from an amorphous section of a thick one with an angle of 70° between them,which is consistent with the [111] axis stacking angle of the crystal.SAED and fast Fourier transform（FFT） patterns reveal that the nanowires can grow along with different axes,and the bamboo-nodes section is full of stacking faults and twin crystal.The twisted SiC lattice planes reveal that the screw dislocation growth is the main mechanism for the CVD-SiC nanowires.
基金Projects(50832004,51105132)supported by the National Natural Science Foundation of ChinaProject(B08040)supported by Program of Introducing Talents of Discipline to Universities,China
文摘Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.
基金Projects(51221001,51202193)supported by the National Natural Science Foundation of ChinaProject(B08040)supported by Program of Introducing Talents of Discipline to Universities,China
文摘Using natural gas as carbon source, 2D needle felt as preform, 2D-C/C composites were prepared by thermal gradient chemical vapor infiltration. Their microstructures were observed under polarized light microscope （PLM） and scanning electron microscope （SEM）, and the flexural behaviors before and after heat-treatment were studied with a universal mechanical testing machine. The fracture mechanism of the composites was discussed in detail. The results show that, carbon matrix exhibits pure smooth laminar （SL） characteristic including numerous wrinkled layered structures and some inter-laminar micro-cracks. With the decreasing density, the strength of the composites decreases and the toughness increases slightly; after 2500 °C heat-treatment, the inter-laminar micro-cracks in matrix increase, the strength decreases, and the toughness obviously increases. The fracture mode of the composites changes from brittle to pseudo-plastic characteristic due to more crack deflections in SL matrix.
基金supported by the National Natural Science Foundation of China(No.50575182)the Natural Science Foundation of Shaanxi Province of China(2014JM7266)
文摘A seal device as an important component of aeroengines has decisive influence on per-formance,reliability,and working life of aeroengines.With the development of aeroengines,demands on the performance characteristics of seal devices are made strictly.Finger seal as a novel kind of sealing device,recently attracts more and more attentions in academic circles and engineer-ing fields at home and abroad.Research on finger seals has been extensively developed,especially on leakage and wear performances under dynamic conditions.However,it is a pity that the work on finger seals has been limited with a single approach that is improving the performance by structural optimization;in addition,the technology of dynamic analysis on finger seals is weak.Aiming at the problems mentioned above,a distributed mass equivalent dynamic model of finger seals considering the coupling effect of overlaid laminates is established in the present paper,the dynamic perfor-mance of 2.5 dimension C/C composite finger seal is analyzed with the model,and then the effects of fiber bundle density and fiber bundle preparation direction on finger seal's dynamic performance are discussed,as well as compared with those of Co-based alloy finger seal.The current work is about dynamic analysis of finger seals and application of C/C composite in this paper may have much academic significance and many engineering values for improving research level of finger seal dynamics and exploring feasibility of C/C composite being used for finger seals.
基金supported by National Science Foundation of China (No. 51405522)the self-fund of State Key Laboratory for Powder Metallurgy (PM-CSU-2015-03)
文摘Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.
基金financially supported by the National Natural Science Foundation of China(Nos.50832004 and 50972120)the 111 Project(No.B08040)
文摘To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the yam unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 ~C. The deviation between the simulated and exl^erimental axial CTE of 3D braided C/C composites is no more than 11%. The effects of different parameters （including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson＇s ratio and CTEs of carbon fibers and carbon matrix） were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson＇s ratio of carbon matrix.
基金the National Natural Science Foundation of China(Nos.51727804,51821091,51872233)Natural Science Basic Research Plan in Shaanxi Province of China(No.2020JQ-175)。
文摘A(ZrC/SiC)_(3)alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical vapor deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m^2.The results indicated that the alternate coating exhibited great ablation resistance,providing an effective protection for C/C composites.In initial rapid heating stage,the(ZrC/SiC)_(3) alternate coating can relieve thermal stress,avoiding the peeling of coating and keeping an intact coating structure.In subsequent ablation,the Si C layers in central region were consumed rapidly,leaving layered interspaces.Three stacked ZrO_(2) layers were reserved with the assistance of the release of thermal stress by interspaces,offering a great anti-scouring effect.In transition and border regions,the alternate Si C layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO_(2).It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.
基金supported by the National Natural Science Foundation of China(No.51105312)the Fundamental Research Funds for the Central University of China(No.3102015JCS05005)
文摘Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast pre- diction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces＂ coefficients of 2.5D CC com- posites are evaluated using multiple linear regression method. Verification experiment has been car- ried out through a group of orthogonal tests. Results indicate that the proposed nmdel is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.
基金Project(200202AA305207) supported by the National High Technology Research and Development Program of China
文摘The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0°/45° weftless fabric lay-up and 0°/45° twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0°/45° weftless composite has a fiat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0°/90° weftless and the 0°/45° twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect （oxidation）, and a little by the thermo-mechanical effect （mechanical denudation）. The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.
文摘A new method for preparation of TaC coating on C/C composite material is reported.The amorphous ethylate tantalum jellied as the precursor is prepared and spread densely on the surface of the C/C composite material so as to form a multilayer film.In a graphitization furnace the multilayer film is transformed into TaC coating at various temperatures.Ethylate tantalum film is characterized by FT-IR(Fourier transform infrared)spectra,XRD(X-ray diffraction)and SEM(scanning electron microscopy)and TaC coating is characterized by XRD and SEM.At 1200℃the coating contained TaC and Ta2O5,and at above 1400℃only TaC is formed.The coating formed at 1600℃is a continuous stratum structure,and that formed at 1600℃is a porous net structure.Analysis on thermodynamics and formation mechanism of TaC indicates that,after ethylate tantalum is decomposed,Ta2O5 is first produced and then transformed into Ta2C,and newly formed Ta2C is transformed into TaC by the sufficient C at last.
基金supported by the National Natural Science Foundation of China (Nos.11272147,10772078)the Aviation Science Foundation (No.2013ZF52074)+1 种基金the State Key Laboratory of Mechanical Structural Mechanics and Control (No.0214G02)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The precise microscopic feature of carbon-carbon（C/C） composites is essential {or an accurate predic tion of their mechanical behavior. After fabrication, actual microscopic feature differs from simple ideal spatial model. Micro computed lomography（CT） scan can well describe internal microstruetures of composites. Therefore, a reconstructed model is developed based on mireo-CT, by a series of prodcedures including extrac tlng components, generating new binary images and establishing a finite element （FE） model. Compared with the model designed by reconstructed commercial software MIMICS. the presented reconstructed FE model is superior in terms of high mesh quality and eontrollable mesh cluantity. The precision of the model is verified by experiment.
基金the financial support from the National Natural Science Foundation of China (Nos. 51675030, 51871010, 52005022)Shanghai Aerospace Scienceand Technology Innovation Fund, China (No. SAST2020-117)。
文摘The novel Ni-based brazing filler was used to join C/C composites.When brazing temperature increased from 1080 to 1100°C,the wetting angle decreased from 23°to 14°,and the brazing filler had good wettability on the surface of C/C composites.The brazing seam of the brazed joint consisted of Ni(s,s)and Cr_(3)C_(2) phases.As brazing temperature increased,lots of Cr_(3)C_(2) phases were generated at the bonding interface,and the thick reaction layer was formed.When brazing temperature was 1120°C,the shear strength of C/C joint reached the maximum value of 31.5 MPa.The fracture path extended in the C/C matrix close to the bonding interface.
基金supported by the Major State Basic Research and Development Program of China (No.2006CB600908)
文摘In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.
文摘The C/C composite brake discs were prepared by tri-cylindrical chemical vapor deposition （CVD） process. The optimum processing parameters were as follows： deposition temperature was 830 - 930 ℃, the gas- flow rates of N2 and propylene were 4.8 - 5.2 m^3/h and 5.8 - 6.2 m^3/h, respectively, the furnace pressure was 4.5 - 5.5 kPa and the deposition time was 200 h. The effects of processing parameters on the densified rates, thermal-physical property and mechanical performance of C/C composite brake discs were studied. The results show that density, heat conductivity, bend strength and abrasion ratio of the multi-cylindrica brake discs are 1. 02 - 1. 78 g/cm^3 , 31 W/（m·K）, 114 MPa and 7μm/s, respectively, which are approximately similar to those of the singlecylindrical ones. The gas tlow rate has no relation to the number of the cylinder and furnace loading. The utilization ratio of carbon can be improved by multi-cylinder CVD process without changing the characteristics of brake disc.
基金supported by the National Natural Sci-ence Foundation of China (No. 50372050)the Foundation of Distinguished Young Scholars (No. 50225210)
文摘2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.
基金the financial supports from the Natural Science Foundation of Hunan Province(Grant No.2019JJ50768)National Natural Science Foundation of China(Grant No.51575536)+1 种基金the National High Technology Research and Development Program(Grant No.2015AA033503)Graduate degree thesis Innovation Foundation of Central South University(Grant No.2018ZZTS414)
文摘Hexagonal boron nitride(h-BN)powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration(CVI)for densification to prepare carbon fiber reinforced/carbon and boron nitride dual matrix composites(C/C-BN).Microstructures and mechanical properties of C/C composites with three different volume contents of h-BN powders were investigated in comparison to pure C/C composites.Results indicated that the introduction of h-BN powders into C/C composites significantly reduced the size of Py C and the anisotropy of thermal contraction in matrix,leading to a gradual disappearance of ring defects as the h-BN content increased.In addition,an enhanced interfacial bonding between fiber and matrix obtained due to higher-textured Py C and rougher fiber surface.Thereby,the flexural strengths and modulus of as-prepared composites decreased firstly and then increased,while the impact toughness presented a decreasing tendency as the content of BN powders increased.Furthermore,with the increasing of h-BN content,anisotropies of compressive properties were weakened,and the compressive strength of C/C-BN composites were always higher than that of pure C/C composit.However,when C/C composites modified by 13.5 vol%content of h-BN,excessive loose BN aggregates appeared in C/C-BN composites,leading to a relatively slight reduction of compressive strength.
