The precise microscopic feature of carbon-carbon(C/C)composites is essential for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model...The precise microscopic feature of carbon-carbon(C/C)composites is essential for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model.Micro-computed-tomography(CT)scan can well describe internal microstructures of composites.Therefore,a reconstructed model is developed based on mirco-CT,by a series of prodcedures including extracting 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 controllable mesh quantity.The precision of the model is verified by experiment.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
By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formatio...By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formation of mesophase in C/C composites, such as pressure, quinoline insolubles (QI) and heterocylic compounds, were analyzed. Further, the graphitizability of the resultant carbon was discussed. The results indicate that to some degree, QI contents accelerate the formation of mesophase at atmospheric pressure; while at high pressure, the coalescence and growth of mesophase spherules are impeded and the resultant coke produced from higher QI content pitch is harder to be graphitized. This is in agreement with the transfer of microstructure from domain anisotropy to fine grained mosaics.展开更多
C/C composites are the emerging materials of choice for aero-engine hot-end components that will bear impact loading in thermal-oxidizing environments. For the components run for extended periods, the safe operation o...C/C composites are the emerging materials of choice for aero-engine hot-end components that will bear impact loading in thermal-oxidizing environments. For the components run for extended periods, the safe operation of components depends on how to evaluate damages under a dynamic load. In this study, Charpy impact tests at a temperature range of 25 to l 200 "C were carried out on C/C composites to verify the effects of temperature induced thermal expansion and oxidation on their impact performance. Below 800 ℃, oxidation was negligible and composites expanding played a leading role, resulting in the remarkable increase in fiber/ matrix interface strength and impact energy. However, when the temperature was above 800 ℃, the release of CO or CO2 due to oxidation resulted in a lower impact energy.展开更多
The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress r...The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress resistance of the composites were therefore computed based on experimental results. The results show that the composite has a very low thermal expansion coefficient. Thermal diffusivity decreases exponentially with temperature increase. The specific heat increases linearly as the temperature rises, and the variation trend of thermal conductivity is similar to that of thermal diffusivity. The thermal stress coefficient of C/C composite has little change with temperature variation, and thermal stress resistance of the composite at high temperature is stable.展开更多
With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-...With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-made furnace.A set of orthogonal experiments were carried out to optimize parameters in terms of indices of density and graphitization degree.The results show the optimal indices can be achieved under the conditions of temperature 650℃,LPGconcentration 80%,gas flux 60 mL/s, total pressure 20 kPa,infiltration time 15 h.The verification experiment proves the effectiveness of the orthogonal experiments. Under the optimal conditions,the graphitization degree of 75%and bulk density of 1.69 g/cm are achieved with a uniform density distribution.At the same time,a new structure is obtained.展开更多
In order to improve the friction-wear properties of the C/C composites for aircraft brake pairs, the fric-tion behavior of samples with infiltrating Si was investigated. The influence of Si smearing thickness on frict...In order to improve the friction-wear properties of the C/C composites for aircraft brake pairs, the fric-tion behavior of samples with infiltrating Si was investigated. The influence of Si smearing thickness on frictionproperties was studied in detail. The results show that with the increase of Si smearing thickness and β-SiC content,the friction coefficient reduces from 0.40 to 0.30; the linear wear of stators increases from 2.0 μm to 18.9 μm percycle, and that of rotors increases from 1.4 μm to 22.6 μm per cycle; mass wear of stators increases from 20.6 mgto 126.9 mg per cycle, and that of rotors increases from 13.7 mg to 166.2 mg per cycle. On the other hand, whena large number of inhomogeneous β-SiC particulates are performed, friction surfaces of the samples flake off layer bylayer and many nicks are observed.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 flat 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
The microstructure and texture of C/C composites with a resin-derived carbon,a rough laminar(RL) pyrocarbon and a smooth laminar pyrocarbon,before and after braking tests,were investigated by Raman spectroscopy.The fu...The microstructure and texture of C/C composites with a resin-derived carbon,a rough laminar(RL) pyrocarbon and a smooth laminar pyrocarbon,before and after braking tests,were investigated by Raman spectroscopy.The full width at half maximum(FWHM) of the D-band indicates the amount of defects in the in-plane lattice,while the G-to-D band intensity(peak area) ratios(IG/ID) is used to evaluate the degree of graphitization.The results show that the FWHM of D-band of sample with RL pyrocarbon changes greatly from 36 cm-1 to 168 cm-1 after braking tests,which indicates that a large number of lattice defects are produced on its wear surface.However,the graphitization degree of resin-derived carbon sample rises significantly,because the IG/ID increases from 0.427 to 0.928.Braking tests under normal loading conditions,involving high temperature and high pressure,produce a lot of lattice defects on the wear surface,and induce the graphitization of the surface.Sample with RL pyrocarbon having a low hardness is easy to deform,and has the most lattice defects on the wear surface after braking.While raw materials with resin-derived carbon have the lowest graphitization degree which rises greatly during braking.展开更多
The 3D fine-woven punctured C/C-(PyC/SiC/TaC)composites,composed of PyC/SiC/TaC interphases and pyrocarbon (PyC)matrix,were synthesized by isothermal chemical vapor infiltration(ICVI)methods.The alternating layers and...The 3D fine-woven punctured C/C-(PyC/SiC/TaC)composites,composed of PyC/SiC/TaC interphases and pyrocarbon (PyC)matrix,were synthesized by isothermal chemical vapor infiltration(ICVI)methods.The alternating layers and the structure of these composites were examined by polarized light microscopy(PLM),X-ray diffractometry(XRD)and scanning electron microscopy(SEM).It is found that the PyC matrix has rough laminar(RL)structure,the TaC layer has NaCl-type cubic structure,and the SiC layer has few wurtzite type 10H-SiC besidesβ-SiC structure.The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated.It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength,and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm 3 ,which is about three times higher than that of samples without TaC/SiC fiber coating.The flexural strength and bending strength increase with increasing the density of the composites.The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites,indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.展开更多
The mathematical modeling for the preparation of C/C composites from propane by F-CVI (Forced-flow Chemical Vapor Infiltration) was studied. The modeling for the actual processes including overturning the preform in t...The mathematical modeling for the preparation of C/C composites from propane by F-CVI (Forced-flow Chemical Vapor Infiltration) was studied. The modeling for the actual processes including overturning the preform in the middle of the deposition process was carried out. Effects of the interval and the number of overturning processes on the time changes of porosity distribution were observed. The actual deposition process could be continued longer by overturning the preform. Furthermore, the total amount of deposition increased twice when several times of overturning were applied. It was confirmed that a low concentration and a slow reaction rate are necessary for a uniform infiltration even when the preform is overturned in the middle of the process.展开更多
The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp...The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.展开更多
The dissimilar materials joining of C/C composites to T2 copper were performed successfully by thermo-compensated Resistance Brazing Welding(RBW)with AgCuTi filler powder.The interfacial microstructure,phase compositi...The dissimilar materials joining of C/C composites to T2 copper were performed successfully by thermo-compensated Resistance Brazing Welding(RBW)with AgCuTi filler powder.The interfacial microstructure,phase composition,and shear strength of the resistance brazed joints were investigated by the relevant analysis method.Experiment results indicated that the order affecting the shear strength of the C/C-Cu joint was welding current,welding pressure,and welding time in turn.The shear strength of backward thermo-compensated RBW was higher than that of forward thermo-compensated RBW due to the Peltier effect.The maximum shear strength of the C/C-Cu joint was 11.56 MPa in the optimized welding parameter with welding current of 8.0 kA,welding time of 60 ms,and welding pressure of 0.10 MPa by backward thermo-compensated RBW.The interface structure at the resistance brazed joint with this welding parameter was C/C composites/TiC/Cu(s.s)/T2 copper.The TiC phase was verified at the interface of the brazed joint by Scanning Electron Microscope(SEM),Energy-Dispersive X-ray Spectrometer(EDS),and X-ray Diffraction(XRD).Considerable fractures occurred in the C/C composites and partial fracture occurred at the interfacial reaction layer.展开更多
Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly ...Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly been studied,whereas the in-plane thermal conductivity has received less attention due to their limited thickness.展开更多
In the present study,the unique three-dimensional graphene coated nickel(Ni/C)foam reinforced silicon carbide(Ni/C@SiC)composites were first obtained via the precursor impregnation and pyrolysis(PIP)processes.The micr...In the present study,the unique three-dimensional graphene coated nickel(Ni/C)foam reinforced silicon carbide(Ni/C@SiC)composites were first obtained via the precursor impregnation and pyrolysis(PIP)processes.The microstructure images indicated that the SiC fillers were successfully prepared in the skeleton pores of the Ni/C foam.The influence of the PIP cycles on the microwave absorption performances was researched,and the results indicated that after the primary PIP process,Ni/C@SiC-I possessed the optimal microwave absorbing performance with a minimum reflection loss(RL)of-25.87 d B at 5.28 GHz and 5.00 mm.Besides,the RL values could be below-10.00 dB from 5.88 GHz to 7.74 GHz when the corresponding matching thickness was 3.85 mm.However,the microwave absorption properties of Ni/C@SiC-II and Ni/C@SiC-Ⅲwere tremendously degraded as the PIP times increased.At last,the electromagnetic parameter,dielectric loss,attenuation constant as well as impedance matching coefficient were further investigated to analyze the absorbing mechanism,which opened a new path for the certain scientific evaluation of the absorbing materials and had extremely important to the defence technology.展开更多
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 for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model.Micro-computed-tomography(CT)scan can well describe internal microstructures of composites.Therefore,a reconstructed model is developed based on mirco-CT,by a series of prodcedures including extracting 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 controllable mesh quantity.The precision of the model is verified by experiment.
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By a polarized light optical microscopy with a hot stage, liquid phase nuclear magnetic resonance 13 C NMR and 1 H NMR, X ray diffractometry and scanning electron microscopy (SEM), the factors that affect the formation of mesophase in C/C composites, such as pressure, quinoline insolubles (QI) and heterocylic compounds, were analyzed. Further, the graphitizability of the resultant carbon was discussed. The results indicate that to some degree, QI contents accelerate the formation of mesophase at atmospheric pressure; while at high pressure, the coalescence and growth of mesophase spherules are impeded and the resultant coke produced from higher QI content pitch is harder to be graphitized. This is in agreement with the transfer of microstructure from domain anisotropy to fine grained mosaics.
基金Funded by the National Natural Science Foundation of China(No.U1134102)
文摘C/C composites are the emerging materials of choice for aero-engine hot-end components that will bear impact loading in thermal-oxidizing environments. For the components run for extended periods, the safe operation of components depends on how to evaluate damages under a dynamic load. In this study, Charpy impact tests at a temperature range of 25 to l 200 "C were carried out on C/C composites to verify the effects of temperature induced thermal expansion and oxidation on their impact performance. Below 800 ℃, oxidation was negligible and composites expanding played a leading role, resulting in the remarkable increase in fiber/ matrix interface strength and impact energy. However, when the temperature was above 800 ℃, the release of CO or CO2 due to oxidation resulted in a lower impact energy.
文摘The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress resistance of the composites were therefore computed based on experimental results. The results show that the composite has a very low thermal expansion coefficient. Thermal diffusivity decreases exponentially with temperature increase. The specific heat increases linearly as the temperature rises, and the variation trend of thermal conductivity is similar to that of thermal diffusivity. The thermal stress coefficient of C/C composite has little change with temperature variation, and thermal stress resistance of the composite at high temperature is stable.
基金Projects(5080211550721003)supported by the National Natural Science Foundation of ChinaProject(2006CB600901)supported by the National Basic Research Program of China
文摘With liquid petrol gas(LPG)as carbon source,carbon felt as porous perform and hydrogen as diluent,C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration(MFCVI)process in a self-made furnace.A set of orthogonal experiments were carried out to optimize parameters in terms of indices of density and graphitization degree.The results show the optimal indices can be achieved under the conditions of temperature 650℃,LPGconcentration 80%,gas flux 60 mL/s, total pressure 20 kPa,infiltration time 15 h.The verification experiment proves the effectiveness of the orthogonal experiments. Under the optimal conditions,the graphitization degree of 75%and bulk density of 1.69 g/cm are achieved with a uniform density distribution.At the same time,a new structure is obtained.
基金Project [1998(1817)] supported by the National High-Technology for Industrial Development of China
文摘In order to improve the friction-wear properties of the C/C composites for aircraft brake pairs, the fric-tion behavior of samples with infiltrating Si was investigated. The influence of Si smearing thickness on frictionproperties was studied in detail. The results show that with the increase of Si smearing thickness and β-SiC content,the friction coefficient reduces from 0.40 to 0.30; the linear wear of stators increases from 2.0 μm to 18.9 μm percycle, and that of rotors increases from 1.4 μm to 22.6 μm per cycle; mass wear of stators increases from 20.6 mgto 126.9 mg per cycle, and that of rotors increases from 13.7 mg to 166.2 mg per cycle. On the other hand, whena large number of inhomogeneous β-SiC particulates are performed, friction surfaces of the samples flake off layer bylayer and many nicks are observed.
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 flat 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.
基金Project(2006CB600906) supported by the National Basic Research Program of China
文摘The microstructure and texture of C/C composites with a resin-derived carbon,a rough laminar(RL) pyrocarbon and a smooth laminar pyrocarbon,before and after braking tests,were investigated by Raman spectroscopy.The full width at half maximum(FWHM) of the D-band indicates the amount of defects in the in-plane lattice,while the G-to-D band intensity(peak area) ratios(IG/ID) is used to evaluate the degree of graphitization.The results show that the FWHM of D-band of sample with RL pyrocarbon changes greatly from 36 cm-1 to 168 cm-1 after braking tests,which indicates that a large number of lattice defects are produced on its wear surface.However,the graphitization degree of resin-derived carbon sample rises significantly,because the IG/ID increases from 0.427 to 0.928.Braking tests under normal loading conditions,involving high temperature and high pressure,produce a lot of lattice defects on the wear surface,and induce the graphitization of the surface.Sample with RL pyrocarbon having a low hardness is easy to deform,and has the most lattice defects on the wear surface after braking.While raw materials with resin-derived carbon have the lowest graphitization degree which rises greatly during braking.
基金Project(50872154)supported by the National Natural Science Foundation of ChinaProject(20080431029)supported by China Postdoctoral Science FoundationProject supported by the Postdoctoral Science Foundation of Central South University,China
文摘The 3D fine-woven punctured C/C-(PyC/SiC/TaC)composites,composed of PyC/SiC/TaC interphases and pyrocarbon (PyC)matrix,were synthesized by isothermal chemical vapor infiltration(ICVI)methods.The alternating layers and the structure of these composites were examined by polarized light microscopy(PLM),X-ray diffractometry(XRD)and scanning electron microscopy(SEM).It is found that the PyC matrix has rough laminar(RL)structure,the TaC layer has NaCl-type cubic structure,and the SiC layer has few wurtzite type 10H-SiC besidesβ-SiC structure.The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated.It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength,and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm 3 ,which is about three times higher than that of samples without TaC/SiC fiber coating.The flexural strength and bending strength increase with increasing the density of the composites.The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites,indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.
文摘The mathematical modeling for the preparation of C/C composites from propane by F-CVI (Forced-flow Chemical Vapor Infiltration) was studied. The modeling for the actual processes including overturning the preform in the middle of the deposition process was carried out. Effects of the interval and the number of overturning processes on the time changes of porosity distribution were observed. The actual deposition process could be continued longer by overturning the preform. Furthermore, the total amount of deposition increased twice when several times of overturning were applied. It was confirmed that a low concentration and a slow reaction rate are necessary for a uniform infiltration even when the preform is overturned in the middle of the process.
基金the Key Projects of Equipment Pre-research Foundation of the Ministry of Equipment Development of the Central Military Commission of China (No.6140922010201)the Key R&D Plan of Zhenjiang in 2018(No.GY2018021)。
文摘The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.
基金supported by the National Natural Science Foundation of China(No.52175305)the Industrial Innovation Major Technology Global Unveiling Project of Jining City,China(No.2022JBZP004)the New and Old Kinetic Energy Conversion Major Industrial Research Projects in Shandong Province in 2021,China.
文摘The dissimilar materials joining of C/C composites to T2 copper were performed successfully by thermo-compensated Resistance Brazing Welding(RBW)with AgCuTi filler powder.The interfacial microstructure,phase composition,and shear strength of the resistance brazed joints were investigated by the relevant analysis method.Experiment results indicated that the order affecting the shear strength of the C/C-Cu joint was welding current,welding pressure,and welding time in turn.The shear strength of backward thermo-compensated RBW was higher than that of forward thermo-compensated RBW due to the Peltier effect.The maximum shear strength of the C/C-Cu joint was 11.56 MPa in the optimized welding parameter with welding current of 8.0 kA,welding time of 60 ms,and welding pressure of 0.10 MPa by backward thermo-compensated RBW.The interface structure at the resistance brazed joint with this welding parameter was C/C composites/TiC/Cu(s.s)/T2 copper.The TiC phase was verified at the interface of the brazed joint by Scanning Electron Microscope(SEM),Energy-Dispersive X-ray Spectrometer(EDS),and X-ray Diffraction(XRD).Considerable fractures occurred in the C/C composites and partial fracture occurred at the interfacial reaction layer.
基金supported by the National Natural Science Foundation of China(Grant Nos.52276086 and 52130604)the Basic Research Program of China(Grant No.514010303-102)the K.C.Wong Education Foundation。
文摘Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly been studied,whereas the in-plane thermal conductivity has received less attention due to their limited thickness.
基金supported by the Fundamental Research Funds for the Central Universities (Grant No. D5000210522 and D5000200408)Jiangsu Planned Projects for Postdoctoral Research Funds, National Natural Science Foundation of China [grant number 51772151]+2 种基金Natural Science Foundation of Shaanxi Province (Grant No. 2021JQ-117)Basic Research Programs of Taicang (Grant No.TC2020JC10)Natural Science Foundation of Shandong Province (Grant No. ZR2020QE180)
文摘In the present study,the unique three-dimensional graphene coated nickel(Ni/C)foam reinforced silicon carbide(Ni/C@SiC)composites were first obtained via the precursor impregnation and pyrolysis(PIP)processes.The microstructure images indicated that the SiC fillers were successfully prepared in the skeleton pores of the Ni/C foam.The influence of the PIP cycles on the microwave absorption performances was researched,and the results indicated that after the primary PIP process,Ni/C@SiC-I possessed the optimal microwave absorbing performance with a minimum reflection loss(RL)of-25.87 d B at 5.28 GHz and 5.00 mm.Besides,the RL values could be below-10.00 dB from 5.88 GHz to 7.74 GHz when the corresponding matching thickness was 3.85 mm.However,the microwave absorption properties of Ni/C@SiC-II and Ni/C@SiC-Ⅲwere tremendously degraded as the PIP times increased.At last,the electromagnetic parameter,dielectric loss,attenuation constant as well as impedance matching coefficient were further investigated to analyze the absorbing mechanism,which opened a new path for the certain scientific evaluation of the absorbing materials and had extremely important to the defence technology.