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
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
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 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 （lC/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 IC/1D 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
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
Metal phosphides have been studied as prospective anode materials for sodium-ion batteries(SIBs)due to their higher specific capacity compared to other anode materials.However,rapid capacity decay and limited cycle li...Metal phosphides have been studied as prospective anode materials for sodium-ion batteries(SIBs)due to their higher specific capacity compared to other anode materials.However,rapid capacity decay and limited cycle life caused by volume expansion and low electrical conductivity of phosphides in SIBs remain still unsolved.To address these issues,GeP_(3) was first prepared by high-energy ball milling,and then Ketjen black(KB)was introduced to synthesize composite GeP_(3)/KB anode materials under controlled milling speed and time by a secondary ball milling process.During the ball milling process,GeP_(3) and KB form strong chemical bonds,resulting in a closely bonded composite.Consequently,the GeP_(3)/KB anodes was demonstrated excellent sodium storage performance,achieving a high reversible capacity of 933.41 mAh·g^(–1) at a current density of 0.05 A·g^(–1) for a special formula of GeP_(3)/KB-600-40 sample prepared at ball milling speed of 600 r/min for 40 h.Even at a high current density of 2 A·g^(–1) over 200 cycles,the capacity remains 314.52 mAh·g^(–1) with a retention rate of 66.6%.In conclusion,this work successfully prepares GeP_(3)/KB anode-carbon composite for electrodes by high-energy ball milling,which can restrict electrode volume expansion,enhance capacity,and improve cycle stability of SIBs.展开更多
As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation ...As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation and fragmentation.This ultimately leads to a decrease in cell capacity.The trends of volume expansion and capacity change of the SiO/graphite(SiO/C)composite electrode during cycling were investigated via in situ expansion monitoring.First,a series of expansion test schemes were designed,and the linear relationship between negative electrode expansion and cell capacity degradation was quantitatively analyzed.Then,the effects of different initial pressures on the long-term cycling performance of the cell were evaluated.Finally,the mechanism of their effects was analyzed by scanning electron microscope.The results show that after 50 cycles,the cell capacity decreases from 2.556 mAh to 1.689 mAh,with a capacity retention ratio(CRR)of only 66.08%.A linear relationship between the capacity retention ratio and thickness expansion was found.Electrochemical measurements and scanning electron microscope images demonstrate that intense stress inhibits the lithiation of the negative electrode and that the electrode is more susceptible to irreversible damage during cycling.Overall,these results reveal the relationship between the cycling performance of SiO and the internal pressure of the electrode from a macroscopic point of view,which provides some reference for the application of SiO/C composite electrodes in lithium-ion batteries.展开更多
Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical micro...Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.展开更多
The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditiona...The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix.Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi_(2),C/C-ZrB_(2)-ZrC-SiC composites prepared by the vacuum infiltration of ZrB_(2) combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases.The mass and linear ablation rates of the C/C-ZrB_(2)-ZrC-SiC composites were respectively 68.9%and 29.7%lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration.The ablation performance was improved because the volatilization of B_(2)O_(3),removes some of the heat,and the more uniformly distributed ZrO_(2),that helps produce a ZrO2-SiO2 continu-ous protective layer,hinders oxygen infiltration and decreases ablation.展开更多
B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treat...B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treatment.The microstructural evolution and mechanical properties were investigated.Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER.The substructured grains reached 66.5%owing to the pinning effect of nano-sized B4C,and the grain size was refined from 3.12μm to 1.56μm after HER.After T6 treatment,dispersed Mg_(2)Si precipitated phases formed,and the grain size increased to 1.87μm.Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg_(2)Si.The stress distributions of as-rolled and heated composites were similar,considering that the T6 heat treatment was only effective in eliminating the first internal stress.The Vickers,microhardness,and tensile strength of as-SPSed composites were greatly improved from HV 55.45,0.86 GPa,and 180 MPa to HV 77.51,1.08 GPa,and 310 MPa,respectively.Despite the precipitation strengthening,the corresponding values of as-heated composites decreased to HV 70.82,0.85 GPa,and 230 MPa owing to grain coarsening.展开更多
The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C 3H 6, C 3H 6 N 2 and C 3H 6 H 2 was investigated respectively. The mechanism on the r...The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C 3H 6, C 3H 6 N 2 and C 3H 6 H 2 was investigated respectively. The mechanism on the role of carrier gas in chemical vapor infiltration was also discussed. The results shows that whether or not adding N 2 as carrier gas has little influences on the densification behavior of C/C composites with the controlled temperature, the partial pressure of hydrocarbon and the effective residence time of the gas phase remain constant. When the controlled temperature is not less than 1 173 K,using N 2 or H 2 as carrier gas makes pronounced differences in densifying of C/C composites. The average bulk density of C/C composites from C 3H 6 H 2 is eight to ten percent higher than that from C 3H 6 N 2. However, when the controlled temperature is not higher than 1 123 K,the densification rate of C/C composites from C 3H 6 H 2 is much lower than that from C 3H 6 N 2, which implies that effects of carrier gas on densification of C/C composites are closely related to the type of carrier gas and infiltration temperature. At higher temperature, using H 2 as carrier gas is favorable to the densification of C/C composites, while at lower temperature, hydrogen, acting as reactive gas, can inhibit the formation of pyrolytic carbon.展开更多
C/C-SiC composites with SiC island distribution Were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition （CVD）, silico...C/C-SiC composites with SiC island distribution Were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition （CVD）, siliconizing, liquid phase impregnation and carbonization. The wear and friction properties were tested by an MM-1000 wet friction machine. The results show that SiC phases are mainly distributed between carbon fibers and pyrocarbons as well as among the pryoearbons. The dynamic friction coefficient of the composites decreases gradually from 0.126 to 0.088 with the increase of the surface pressure from 0.5 to 2.5 MPa at the same rotary speed. Furthermore, under the constant surface pressure, the dynamic friction coefficient increases from 0.114 to 0.126 with the increase of the rotary speed from 1 500 to 2 500 r/min. However, the coefficient decreases to 0.104 when the rotary speed exceeds 4 500 r/min. During the friction process, the friction coefficient of C/C-SiC composite is between 0.088 and 0.126, and the wear value is zero after 300 times brake testing.展开更多
Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the compo...Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the composites before and after erosion.The results indicate that a U shape relationship curve presents between the erosion rates and Al content,and the lowest erosion rate occurs at 40 wt%Al.Except for the important influence of compactness,the increasing soft Al mixed with reactive SiC,namely the mixture located between carbon and residual Si also,plays a key role in the erosion of the C/C-SiC composites through crack deflection,plastic deformation and bonding cracked Si.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
Using low-cost FePO4·2H2O as iron source,Na2FePO4F/C composite is prepared by alcohol-assisted ball milling and solid-state reaction method.The XRD pattern of Na2FePO4F/C composite demonstrates sharp peaks,indica...Using low-cost FePO4·2H2O as iron source,Na2FePO4F/C composite is prepared by alcohol-assisted ball milling and solid-state reaction method.The XRD pattern of Na2FePO4F/C composite demonstrates sharp peaks,indicating high crystalline and phase purity.The SEM and TEM images reveal that diameter of the spherical-like Na2FePO4F/C particles ranges from 50 to 300 nm,and HRTEM image shows that the surface of Na2FePO4F/C composite is uniformly coated by carbon layer with a average thickness of about 3.6 nm.The carbon coating constrains the growth of the particles and effectively reduces the agglomeration of nanoparticles.Using lithium metal as anode,the composite delivers a discharge capacities of 102.8,96.4 and 90.3 mA·h/g at rates of 0.5C,1C and 2C,respectively.After 100 cycles at 0.5C,a discharge capacity of 98.9 mA·h/g is maintained with capacity retention of 96.2%.The Li+diffusion coefficient(D)of Na2FePO4F/C composite is calculated as 1.71×10^–9 cm^2/s.This study reveals that the simple solid state reaction could be a practical and effective synthetic route for the industrial production of Na2FePO4F/C material.展开更多
A LiFePO4/（C＋Fe2P） composite cathode material was prepared by a sol-gel method using Fe（NO3）3.9H20, LiAc·H2O）, NHaH2PO4 and citric acid as raw materials, and the physical properties and electrochemical perf...A LiFePO4/（C＋Fe2P） composite cathode material was prepared by a sol-gel method using Fe（NO3）3.9H20, LiAc·H2O）, NHaH2PO4 and citric acid as raw materials, and the physical properties and electrochemical performance of the composite cathode material were investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical tests. The Fe2P content, morphology and electrochemical performance of LiFePOa/（C＋Fe2P） composite depend on the calcination temperature. The optimized LiFePO4/（C＋FeeP） composite is prepared at 650 ~C and the optimized composite exhibits sphere-like morphology with porous structure and Fe2P content of about 3.2% （mass fraction）. The discharge capacity of the optimized LiFePO4/（C＋FeRP） at 0.1C is 156 and 161 mA.h/g at 25 and 55 ℃, respectively, and the corresponding capacity retentions are 96% after 30 cycles; while the capacity at 1C is 142 and 149 mA.h/g at 25 and 55 ℃, respectively, and the capacity still remains 135 and 142 mA-h/g after 30 cycles at 25 and 55℃, respectively.展开更多
Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) ...Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.展开更多
Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of...Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.展开更多
This work considered the influence of Cr3 C2 particle loading on microstructure and mechanical properties of Zn-SiC-Cr3 C2 nanocomposite produced via electrocodeposition are investigated. The surface nature of the nan...This work considered the influence of Cr3 C2 particle loading on microstructure and mechanical properties of Zn-SiC-Cr3 C2 nanocomposite produced via electrocodeposition are investigated. The surface nature of the nanocomposite coatings were characterized using scanning electron microscope(SEM)coupled with the energy dispersive spectrometer(EDS). Abrasive wear behaviour and hardness property of Zn-SiC-Cr3 C2 nanocomposite produced were investigated using CERT UMT-2 multi-functional tribological tester and Dura Scan hardness tester. The corrosion property was evaluated through linear polarization approach. The result showed that the coatings exhibited good stability and Cr_3 C_2 nanocomposite loading significantly improved the micro structural performance, hardness property,wear resistance as well as corrosion resistance of the coatings.展开更多
Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the tempe...Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the temperatures from 450 °C to 850 °C with the strain rates from 0.001 s-1 to 1 s-1. The results show that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow true stress-strain curves of the composite, and the peak stress increases with the decreasing deformation temperature or the increasing strain rate. The thermal deformation activation energy was calculated as 170.732 k J/mol and the constitutive equation was established. The inflection point in the lnθ-ε curve appears and the minimum value of-(lnθ)/ε-ε curve is presented when the critical state is attained for this composite. The critical strain increases with the increasing strain rate or the decreasing deformation temperature. There is linear relationship between critical strain and peak strain, i.e., εc=0.572εp. The predicting model of critical strain is described by the function of εc=1.062×10-2Z0.0826.展开更多
This paper calculated load-carrying of isogrid and orthogrid of carbon-epoxy composite trellis wound structure(C/E CTWS) using non-linear finite element method.Based on the analysis,test cases were designed and tests ...This paper calculated load-carrying of isogrid and orthogrid of carbon-epoxy composite trellis wound structure(C/E CTWS) using non-linear finite element method.Based on the analysis,test cases were designed and tests of axial compression were carried.Analysis result and test result fit well.In order to be used in the project,this kind of structure cut-out repairing was calculated.The method presented in this paper has been proved and can be used to solve complicated engineering problems.According to calculations and experimental results combined with application,a principle of choosing wound structure is obtained and principle could be applied to engineering.展开更多
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 （lC/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 IC/1D 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 [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National Natural Science Foundation of China Young Scientist Fund(22105120)Shaanxi Province Qin Chuangyuan“Scientist+Engineer”Team Construction Project(2024QCY-KXJ-127)。
文摘Metal phosphides have been studied as prospective anode materials for sodium-ion batteries(SIBs)due to their higher specific capacity compared to other anode materials.However,rapid capacity decay and limited cycle life caused by volume expansion and low electrical conductivity of phosphides in SIBs remain still unsolved.To address these issues,GeP_(3) was first prepared by high-energy ball milling,and then Ketjen black(KB)was introduced to synthesize composite GeP_(3)/KB anode materials under controlled milling speed and time by a secondary ball milling process.During the ball milling process,GeP_(3) and KB form strong chemical bonds,resulting in a closely bonded composite.Consequently,the GeP_(3)/KB anodes was demonstrated excellent sodium storage performance,achieving a high reversible capacity of 933.41 mAh·g^(–1) at a current density of 0.05 A·g^(–1) for a special formula of GeP_(3)/KB-600-40 sample prepared at ball milling speed of 600 r/min for 40 h.Even at a high current density of 2 A·g^(–1) over 200 cycles,the capacity remains 314.52 mAh·g^(–1) with a retention rate of 66.6%.In conclusion,this work successfully prepares GeP_(3)/KB anode-carbon composite for electrodes by high-energy ball milling,which can restrict electrode volume expansion,enhance capacity,and improve cycle stability of SIBs.
基金supported by the Fundamental Research Funds for the Central Universities(WK2090000055)Anhui Provincial Natural Science Foundation of China(2308085QG231).
文摘As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation and fragmentation.This ultimately leads to a decrease in cell capacity.The trends of volume expansion and capacity change of the SiO/graphite(SiO/C)composite electrode during cycling were investigated via in situ expansion monitoring.First,a series of expansion test schemes were designed,and the linear relationship between negative electrode expansion and cell capacity degradation was quantitatively analyzed.Then,the effects of different initial pressures on the long-term cycling performance of the cell were evaluated.Finally,the mechanism of their effects was analyzed by scanning electron microscope.The results show that after 50 cycles,the cell capacity decreases from 2.556 mAh to 1.689 mAh,with a capacity retention ratio(CRR)of only 66.08%.A linear relationship between the capacity retention ratio and thickness expansion was found.Electrochemical measurements and scanning electron microscope images demonstrate that intense stress inhibits the lithiation of the negative electrode and that the electrode is more susceptible to irreversible damage during cycling.Overall,these results reveal the relationship between the cycling performance of SiO and the internal pressure of the electrode from a macroscopic point of view,which provides some reference for the application of SiO/C composite electrodes in lithium-ion batteries.
基金Project(61391) supported by the National Security Basic Research Program of ChinaProject (91016029) supported by the National Natural Science Foundation of China
文摘Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.
文摘The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix.Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi_(2),C/C-ZrB_(2)-ZrC-SiC composites prepared by the vacuum infiltration of ZrB_(2) combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases.The mass and linear ablation rates of the C/C-ZrB_(2)-ZrC-SiC composites were respectively 68.9%and 29.7%lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration.The ablation performance was improved because the volatilization of B_(2)O_(3),removes some of the heat,and the more uniformly distributed ZrO_(2),that helps produce a ZrO2-SiO2 continu-ous protective layer,hinders oxygen infiltration and decreases ablation.
基金Projects(51775366,51805358)supported by the National Natural Science Foundation of ChinaProject(20130321024)supported by the Key Science and Technology Program of Shanxi Province,China。
文摘B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treatment.The microstructural evolution and mechanical properties were investigated.Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER.The substructured grains reached 66.5%owing to the pinning effect of nano-sized B4C,and the grain size was refined from 3.12μm to 1.56μm after HER.After T6 treatment,dispersed Mg_(2)Si precipitated phases formed,and the grain size increased to 1.87μm.Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg_(2)Si.The stress distributions of as-rolled and heated composites were similar,considering that the T6 heat treatment was only effective in eliminating the first internal stress.The Vickers,microhardness,and tensile strength of as-SPSed composites were greatly improved from HV 55.45,0.86 GPa,and 180 MPa to HV 77.51,1.08 GPa,and 310 MPa,respectively.Despite the precipitation strengthening,the corresponding values of as-heated composites decreased to HV 70.82,0.85 GPa,and 230 MPa owing to grain coarsening.
文摘The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C 3H 6, C 3H 6 N 2 and C 3H 6 H 2 was investigated respectively. The mechanism on the role of carrier gas in chemical vapor infiltration was also discussed. The results shows that whether or not adding N 2 as carrier gas has little influences on the densification behavior of C/C composites with the controlled temperature, the partial pressure of hydrocarbon and the effective residence time of the gas phase remain constant. When the controlled temperature is not less than 1 173 K,using N 2 or H 2 as carrier gas makes pronounced differences in densifying of C/C composites. The average bulk density of C/C composites from C 3H 6 H 2 is eight to ten percent higher than that from C 3H 6 N 2. However, when the controlled temperature is not higher than 1 123 K,the densification rate of C/C composites from C 3H 6 H 2 is much lower than that from C 3H 6 N 2, which implies that effects of carrier gas on densification of C/C composites are closely related to the type of carrier gas and infiltration temperature. At higher temperature, using H 2 as carrier gas is favorable to the densification of C/C composites, while at lower temperature, hydrogen, acting as reactive gas, can inhibit the formation of pyrolytic carbon.
基金Project(2006CB600901) supported by the Major State Basic Research and Development Program of ChinaProject(0991015) supported by Guangxi Science Found, ChinaProject(200808MS083) supported by Guangxi Education Department Found
文摘C/C-SiC composites with SiC island distribution Were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition （CVD）, siliconizing, liquid phase impregnation and carbonization. The wear and friction properties were tested by an MM-1000 wet friction machine. The results show that SiC phases are mainly distributed between carbon fibers and pyrocarbons as well as among the pryoearbons. The dynamic friction coefficient of the composites decreases gradually from 0.126 to 0.088 with the increase of the surface pressure from 0.5 to 2.5 MPa at the same rotary speed. Furthermore, under the constant surface pressure, the dynamic friction coefficient increases from 0.114 to 0.126 with the increase of the rotary speed from 1 500 to 2 500 r/min. However, the coefficient decreases to 0.104 when the rotary speed exceeds 4 500 r/min. During the friction process, the friction coefficient of C/C-SiC composite is between 0.088 and 0.126, and the wear value is zero after 300 times brake testing.
基金Project(51902239)supported by the National Natural Science Foundation of ChinaProject(2020JQ-808)supported by the Science and Technology Fund of Shaanxi Province,China+3 种基金Projects(19JK0400,19JK0402)supported by the Education Fund of Shaanxi Province,ChinaProject(SKLSP201752)supported by the State Key Laboratory of Solidification Processing in Northwestern Poly Technical University,ChinaProject(XAGDXJJ17008)supported by the Principal Fund of Xi’an Technological University,ChinaProject supported by the Youth Innovation Team of Shaanxi Universities,China。
文摘Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the composites before and after erosion.The results indicate that a U shape relationship curve presents between the erosion rates and Al content,and the lowest erosion rate occurs at 40 wt%Al.Except for the important influence of compactness,the increasing soft Al mixed with reactive SiC,namely the mixture located between carbon and residual Si also,plays a key role in the erosion of the C/C-SiC composites through crack deflection,plastic deformation and bonding cracked Si.
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.
基金Projects(51472211,51502256)supported by the National Natural Science Foundation of ChinaProjects(2016GK4005,2016GK4030)supported by the Strategic New Industry of Hunan Province,ChinaProject(13C925)supported by the Research Foundation of Education Bureau of Hunan Province,China
文摘Using low-cost FePO4·2H2O as iron source,Na2FePO4F/C composite is prepared by alcohol-assisted ball milling and solid-state reaction method.The XRD pattern of Na2FePO4F/C composite demonstrates sharp peaks,indicating high crystalline and phase purity.The SEM and TEM images reveal that diameter of the spherical-like Na2FePO4F/C particles ranges from 50 to 300 nm,and HRTEM image shows that the surface of Na2FePO4F/C composite is uniformly coated by carbon layer with a average thickness of about 3.6 nm.The carbon coating constrains the growth of the particles and effectively reduces the agglomeration of nanoparticles.Using lithium metal as anode,the composite delivers a discharge capacities of 102.8,96.4 and 90.3 mA·h/g at rates of 0.5C,1C and 2C,respectively.After 100 cycles at 0.5C,a discharge capacity of 98.9 mA·h/g is maintained with capacity retention of 96.2%.The Li+diffusion coefficient(D)of Na2FePO4F/C composite is calculated as 1.71×10^–9 cm^2/s.This study reveals that the simple solid state reaction could be a practical and effective synthetic route for the industrial production of Na2FePO4F/C material.
基金Project(50571091) supported by the National Natural Science Foundation of ChinaProject(09C947) supported by the Scientific Research Fund of Hunan Provincial Education Department,China
文摘A LiFePO4/（C＋Fe2P） composite cathode material was prepared by a sol-gel method using Fe（NO3）3.9H20, LiAc·H2O）, NHaH2PO4 and citric acid as raw materials, and the physical properties and electrochemical performance of the composite cathode material were investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical tests. The Fe2P content, morphology and electrochemical performance of LiFePOa/（C＋Fe2P） composite depend on the calcination temperature. The optimized LiFePO4/（C＋FeeP） composite is prepared at 650 ~C and the optimized composite exhibits sphere-like morphology with porous structure and Fe2P content of about 3.2% （mass fraction）. The discharge capacity of the optimized LiFePO4/（C＋FeRP） at 0.1C is 156 and 161 mA.h/g at 25 and 55 ℃, respectively, and the corresponding capacity retentions are 96% after 30 cycles; while the capacity at 1C is 142 and 149 mA.h/g at 25 and 55 ℃, respectively, and the capacity still remains 135 and 142 mA-h/g after 30 cycles at 25 and 55℃, respectively.
基金Project(51271012)supported by the National Natural Science Foundation of China
文摘Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.
基金Project (2005CB623703) supported by the Major State Basic Research and Development Program of ChinaProject (2008AA030502) supported by the National High-Tech Research and Development Program of China
文摘Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.
基金National Research FoundationSurface Engineering Research Centre (SERC)+1 种基金Tshwane University of Technology,Pretoria,South Africa were acknowledge for their supportCovenant University Centre for Research Innovation and Discovery (CUCRID) Ota, Nigeria for the provision of financial support
文摘This work considered the influence of Cr3 C2 particle loading on microstructure and mechanical properties of Zn-SiC-Cr3 C2 nanocomposite produced via electrocodeposition are investigated. The surface nature of the nanocomposite coatings were characterized using scanning electron microscope(SEM)coupled with the energy dispersive spectrometer(EDS). Abrasive wear behaviour and hardness property of Zn-SiC-Cr3 C2 nanocomposite produced were investigated using CERT UMT-2 multi-functional tribological tester and Dura Scan hardness tester. The corrosion property was evaluated through linear polarization approach. The result showed that the coatings exhibited good stability and Cr_3 C_2 nanocomposite loading significantly improved the micro structural performance, hardness property,wear resistance as well as corrosion resistance of the coatings.
基金Project(51101052) supported by the National Natural Science Foundation of China
文摘Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the temperatures from 450 °C to 850 °C with the strain rates from 0.001 s-1 to 1 s-1. The results show that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow true stress-strain curves of the composite, and the peak stress increases with the decreasing deformation temperature or the increasing strain rate. The thermal deformation activation energy was calculated as 170.732 k J/mol and the constitutive equation was established. The inflection point in the lnθ-ε curve appears and the minimum value of-(lnθ)/ε-ε curve is presented when the critical state is attained for this composite. The critical strain increases with the increasing strain rate or the decreasing deformation temperature. There is linear relationship between critical strain and peak strain, i.e., εc=0.572εp. The predicting model of critical strain is described by the function of εc=1.062×10-2Z0.0826.
文摘This paper calculated load-carrying of isogrid and orthogrid of carbon-epoxy composite trellis wound structure(C/E CTWS) using non-linear finite element method.Based on the analysis,test cases were designed and tests of axial compression were carried.Analysis result and test result fit well.In order to be used in the project,this kind of structure cut-out repairing was calculated.The method presented in this paper has been proved and can be used to solve complicated engineering problems.According to calculations and experimental results combined with application,a principle of choosing wound structure is obtained and principle could be applied to engineering.
