With vigorous developments in nanotechnology,the elaborate regulation of microstructure shows attractive potential in the design of electromagnetic wave absorbers.Herein,a hierarchical porous structure and composite h...With vigorous developments in nanotechnology,the elaborate regulation of microstructure shows attractive potential in the design of electromagnetic wave absorbers.Herein,a hierarchical porous structure and composite heterogeneous interface are constructed successfully to optimize the electromagnetic loss capacity.The macro–micro-synergistic graphene aerogel formed by the ice template‑assisted 3D printing strategy is cut by silicon carbide nanowires(SiC_(nws))grown in situ,while boron nitride(BN)interfacial structure is introduced on graphene nanoplates.The unique composite structure forces multiple scattering of incident EMWs,ensuring the combined effects of interfacial polarization,conduction networks,and magnetic-dielectric synergy.Therefore,the as-prepared composites present a minimum reflection loss value of−37.8 dB and a wide effective absorption bandwidth(EAB)of 9.2 GHz(from 8.8 to 18.0 GHz)at 2.5 mm.Besides,relying on the intrinsic high-temperature resistance of SiC_(nws) and BN,the EAB also remains above 5.0 GHz after annealing in air environment at 600℃ for 10 h.展开更多
Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession r...Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession rate of 0.15μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m^(2)(2000℃)for 300 s.Associated with the temperature gradient of the ablation surface,the oxidation products at different locations mainly consist of(TiZrHfNbTa)O_(x),(Zr_(x)Hf_(1-x))6(NbyTa_(1-y))_(2)O_(17),Ti(Nb_(x)Ta_(1-x))_(2)O_(7),(Hf_(x)Zr_(1-x))SiO_(4),and SiO_(2).Due to the synergistic effect of the multi-component oxides,oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases.It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring.It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.展开更多
To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,f...To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,flexibility,exceptional mechanical strength,and superior electrothermal and photothermal properties,particularly for flexible and wearable electronics.In this regard,we designed an absorption-based composite film comprising carbon nanotubes(CNT)and α-Fe_(2)O_(3),featuring a CNT layer sandwiched between twoα-Fe_(2)O_(3)layers on the upper and lower surfaces.This composite film was fabricated through an electrodeposition process followed by a thermal annealing procedure to achieve enhanced EMI shielding performance along with improved electrothermal and photothermal properties.The strategically designed sandwich structure allows the rough surface of the upper α-Fe_(2)O_(3)layer to not only improve the impedance mismatch between free space and the composite film,facilitating the penetration of incident electromagnetic(EM)waves into the film and promoting increased EM absorption rather than reflection,but also to enhance electrical conductivity,thereby improving electron mobility and density.Consequently,the average total shielding effectiveness(SE)of the CNT/Fe_(16)-300 composite demonstrates remarkable EMI shielding effectiveness(EMI SE:56.8 dB).Furthermore,the alteration in the absorption-to-reflection ratio(A/R)signifies a transition in the EMI shielding mechanism from reflection(0.69 for the pristine CNT film)to absorption(1.86 for the CNT/Fe_(16)-300)with the incremental deposition of α-Fe_(2)O_(3)nanoparticles.This work presents a feasible manufacturing approach for developing composite films with a sandwich structure that exhibits absorption-dominant EMI shielding capabilities,contributing to advancements in thermal management and multifunctional electromagnetic shielding applications.展开更多
C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene fl...C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.展开更多
Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are ve...Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.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
SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the c...SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.展开更多
To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffra...To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.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
In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites b...In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy）. Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re- sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.展开更多
Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum si...Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum silicate（LAS） glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites（1.75 g/cm3） with a CVD-SiC coating to the C/C-SiC composites with a low density（1.48 g/cm3）.The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.展开更多
Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mecha...Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,the mechanical denudation of the sample only containing acicular crystals and the coating spallation caused by superfluous gaseous products of the sample with the sublayer composed of nanocrystals both indicate their inferior anti-ablation properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.展开更多
A SiC whisker-toughened MoSi2-SiC-Si coating was prepared on carbon/carbon (C/C) composites surface by a two-step technique of slurry and pack cementation, and the effects of thermal shock and oxidation on the mechani...A SiC whisker-toughened MoSi2-SiC-Si coating was prepared on carbon/carbon (C/C) composites surface by a two-step technique of slurry and pack cementation, and the effects of thermal shock and oxidation on the mechanical property of the coated C/C were studied. The flexural strength of C/C composites was improved by 6.8% after coated by SiC whisker-toughened MoSi2-SiC-Si. After thermal cycle between 1773 K and room temperature in air for 10 times, the mass loss of the coated sample was 5.08% and the percentage of remaining strength was 81.97%. After oxidation at 1773K in air for 60 min, the mass loss of the coated sample was 2.57% and the percentage of remaining strength was 89.63%. The decrease of the flexural strength during the thermal cycle and oxidation tests was primarily due to the oxidation of C/C substrate resulting from the cracking of coating.展开更多
C/C-HfC-SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in t...C/C-HfC-SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in the heat flux of 2.38 MW/m2 （HF-L） and 4.18 MW/m2 （HF-H） for 60 s. The mechanical denudation in 4.18 MW/m2 （HF-H） was higher than that in 2.38 MW/m2 （HF-L）, while the results indicated that the composites had a similar and good ablation property under two different flame conditions. C/C- HfC-SiC composites can adapt the heat flux from 2.38 MW/m2 to 4.18 MW/m2. The Hf02 was not melted completely in the heat flux of 2.38 MW/m2 （HF-L）. So, both Hf02 and Si02 layers acted as an effective barrier to the transfer of heat and oxidative gases into the underlying carbon substrate. SiO2 was severely consumed in 4.18 MW/m2 （HF-H）, where the HfO2 molten layer played a more important role in protecting the inner composite.展开更多
A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were st...A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.展开更多
The initial geometric imperfection is one of the primary factors affecting the buckling behaviors of composite cylindrical shells under hydrostatic pressure.In this study,ovality and thickness variations as two repres...The initial geometric imperfection is one of the primary factors affecting the buckling behaviors of composite cylindrical shells under hydrostatic pressure.In this study,ovality and thickness variations as two representative types of the geometric imperfections are considered.After measuring the geometric imperfections,a typical carbon fiber reinforced polymers(CFRP)cylindrical shell is tested to obtain the buckling pressure.The buckling behaviors of the shell sample are analyzed in combination with the strain responses.By using the nonlinear numerical analysis,the buckling shapes of the CFRP cylinder shells with different combinations of ovality and thickness variation are firstly discussed.The rules of influence of such imperfections on the buckling pressure are then obtained by nonlinear regression method.Finally,an empirical formula is proposed to predict the buckling pressure of the composite cylinder shells,and the calculated results from the formula are in good agreement with the numerical results.展开更多
High-purity carbon nanotubes （CNTs） with different orientation and lengths were grafted on carbon fibers （CFs） in woven fabrics by using double injection chemical vapor deposition and adjusting the growth temperat...High-purity carbon nanotubes （CNTs） with different orientation and lengths were grafted on carbon fibers （CFs） in woven fabrics by using double injection chemical vapor deposition and adjusting the growth temperature. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman investigations reveal that the grafted CNTs change from being predominantly aligned and uniform in di- ameter to absolutely disordered and variable in diameter, whilst they show significantly increased crystallinity, as the growth temperature is increased from 730 ~C to 870 ~C. In tensile tests of fiber bundles, much more strength degradation of CFs was observed after the growth process at higher temperature than that at lower temperature. These hybrid preforms produced at different growth temperatures were used to reinforce carbon/carbon （C/C） composites. An increment of 34.4% in out-of-plane compressive strength （OCS） was obtained for the composites containing CNTs grown at 730℃, while the OCS increment exhibits an obvious decrease with increasing the growth temperature. Compared with the higher growth temperature, the lower temperature contributes to the decrease in the strength loss of reinforcing fibers and meanwhile the growth of large extending length of CNTs, which can provide long reinforcement to the pyrocarbon matrix, and thus increase the compressive strength better.展开更多
C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of ...C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of the composites were analyzed by scanning electron microscopy and X-ray diffraction. The ablation resistance of the composites was evaluated under 3,000 °C oxyacetylene torch. After ablation for 120 s, the composites exhibit good ablation properties with the linear and mass ablation rates of 9.1 9 10-4mm/s and 1.30 9 10-3g/s, which are far lower than those of the C/C–SiC composites. The excellent ablative property of the C/C–SiC–HfC composites is resulted from the formation of HfO2 molten layer on the surface of the composites, which could play a positive role in reducing heat transfer and preventing oxygen transport to the underlying carbon substrate.展开更多
Carbon fiber reinforced AZ91 D matrix composites with pyrolytic（PyC） coating deposited on fiber surface（PyC-Cf/AZ91 D composites） have been fabricated by Liquid-solid extrusion following vacuum pressure infiltrati...Carbon fiber reinforced AZ91 D matrix composites with pyrolytic（PyC） coating deposited on fiber surface（PyC-Cf/AZ91 D composites） have been fabricated by Liquid-solid extrusion following vacuum pressure infiltration technique（LSEVI）. Interfacial microstructure and failure behavior of the composites were investigated. Instead of interfacial reaction products, block-shaped interfacial precipitates Mg（17） Al（12） were detected at the interface, which indicates that interfacial reaction was restrained by LSEVI and PyC coating. Nano-MgO was detected at the interface. Interfacial failure behavior of the PyC-Cf/AZ91 D composites,which was the failure between PyC coating and AZ91 D alloy due to the mismatch of thermal expansion and relatively poor bonding, was proposed. Fracture surface of the PyC-Cf/AZ91 D composites was characterized by fibers pulling-out tests. PyC coating served not only as protection to the fibers, but also an adjustment of the interface of the composites.展开更多
Si-SiC coating was prepared on the surface of carbon/carbon （C/C） composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechani...Si-SiC coating was prepared on the surface of carbon/carbon （C/C） composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between !773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.展开更多
基金sponsored by National Natural Science Foundation of China(No.52302121,No.52203386)Shanghai Sailing Program(No.23YF1454700)+1 种基金Shanghai Natural Science Foundation(No.23ZR1472700)Shanghai Post-doctoral Excellent Program(No.2022664).
文摘With vigorous developments in nanotechnology,the elaborate regulation of microstructure shows attractive potential in the design of electromagnetic wave absorbers.Herein,a hierarchical porous structure and composite heterogeneous interface are constructed successfully to optimize the electromagnetic loss capacity.The macro–micro-synergistic graphene aerogel formed by the ice template‑assisted 3D printing strategy is cut by silicon carbide nanowires(SiC_(nws))grown in situ,while boron nitride(BN)interfacial structure is introduced on graphene nanoplates.The unique composite structure forces multiple scattering of incident EMWs,ensuring the combined effects of interfacial polarization,conduction networks,and magnetic-dielectric synergy.Therefore,the as-prepared composites present a minimum reflection loss value of−37.8 dB and a wide effective absorption bandwidth(EAB)of 9.2 GHz(from 8.8 to 18.0 GHz)at 2.5 mm.Besides,relying on the intrinsic high-temperature resistance of SiC_(nws) and BN,the EAB also remains above 5.0 GHz after annealing in air environment at 600℃ for 10 h.
基金supported by the National Key R&D Program of China(No.2022YFB3707700)the Program of Shanghai Academic/Technology Research Leader(No.23XD1424300)the National Natural Science Foundation of China(No.52332003).
文摘Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession rate of 0.15μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m^(2)(2000℃)for 300 s.Associated with the temperature gradient of the ablation surface,the oxidation products at different locations mainly consist of(TiZrHfNbTa)O_(x),(Zr_(x)Hf_(1-x))6(NbyTa_(1-y))_(2)O_(17),Ti(Nb_(x)Ta_(1-x))_(2)O_(7),(Hf_(x)Zr_(1-x))SiO_(4),and SiO_(2).Due to the synergistic effect of the multi-component oxides,oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases.It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring.It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.
基金financially supported by the National Natural Science Foundation of China(Nos.52222202 and 51772310)Chinese Academy of Sciences Key Research Program of Frontier Sciences(No.QYZDY-SSWJSC031)Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(No.JCYJ-SHFY-2021-001).
文摘To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,flexibility,exceptional mechanical strength,and superior electrothermal and photothermal properties,particularly for flexible and wearable electronics.In this regard,we designed an absorption-based composite film comprising carbon nanotubes(CNT)and α-Fe_(2)O_(3),featuring a CNT layer sandwiched between twoα-Fe_(2)O_(3)layers on the upper and lower surfaces.This composite film was fabricated through an electrodeposition process followed by a thermal annealing procedure to achieve enhanced EMI shielding performance along with improved electrothermal and photothermal properties.The strategically designed sandwich structure allows the rough surface of the upper α-Fe_(2)O_(3)layer to not only improve the impedance mismatch between free space and the composite film,facilitating the penetration of incident electromagnetic(EM)waves into the film and promoting increased EM absorption rather than reflection,but also to enhance electrical conductivity,thereby improving electron mobility and density.Consequently,the average total shielding effectiveness(SE)of the CNT/Fe_(16)-300 composite demonstrates remarkable EMI shielding effectiveness(EMI SE:56.8 dB).Furthermore,the alteration in the absorption-to-reflection ratio(A/R)signifies a transition in the EMI shielding mechanism from reflection(0.69 for the pristine CNT film)to absorption(1.86 for the CNT/Fe_(16)-300)with the incremental deposition of α-Fe_(2)O_(3)nanoparticles.This work presents a feasible manufacturing approach for developing composite films with a sandwich structure that exhibits absorption-dominant EMI shielding capabilities,contributing to advancements in thermal management and multifunctional electromagnetic shielding applications.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51221001 and 51272213)the Foundation for the Author of National Excellent Doctoral Dissertation of China 201036+1 种基金the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (Grant No. 25-TZ-2009)the "111" Project (Grant No. B08040)
文摘C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.
基金supported by the National Natural Science Foundation of China(Nos.91860203,51821091,51872239,52002321 and 52061135102)the China Postdoctoral Science Foundation(No.2019M660265)+3 种基金the Fundamental Research Funds for the Central Universities(China,Nos.G2019KY05116,G2020KY05125)the Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD003)the Creative Research Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(Nos.614291102010517,5050200015 and 5150200033)the Shaanxi Provincial Education Department of China(No.2020JQ-170)。
文摘Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.
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financial support of the project from the National Natural Science Foundation of China(No.51821091 and 51872233)the Research Foundation of Chengdu University of Technology(No.10912-KYQD202008264)。
文摘SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.
基金supported by the National Natural Science Foundation of China under Grant Nos. U1435202 and 51521061the “111” Project under Grant No. 08040the Research Fund of the State Key Laboratory of Solidification Processing (Northwestern Polytechnical University), China (Grant No. 142-TZ-2016)
文摘To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.
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supported by the National Natural Science Foundation of China under Grant No.90716024the"111"Introducing Intelligence Project under Grant No.08040.
文摘In order to improve the anti-oxidation property of carbon/carbon （C/C） composites, a novel SiC-Si-ZrSiO4 multiphase oxidation protective coating was produced on the surface of C/SiC coated carbon/carbon compo ites by a pack cementation technique. The phase composition and microstructure of the as-prepared coatings were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy）. Oxidation behavior of the multiphase coated C/C composites was also investigated. It showed that the as-prepared coating characterized by excellent oxidation resistance and thermal shock re- sistance could effectively protect C/C composites from oxidation at 1773 K for 57 h in air and endure the thermal cycle between 1773 K and room temperature for 12 times, whereas the corresponding weight loss is only 1.47%. The excellent oxidation protective ability of the SiC-Si-ZrSiO4 coating could be attributed to the C/SiC gradient inner layer and the multiphase microstructure of the coating.
基金funding supported from the National Natural Science Foundation of China(Grant Nos.51221001 and 51222207)the "111" Project(Grant No.B08040)the Foundation of the National Excellent Doctoral Dissertation of China(No.201036)
文摘Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2（LMAS） was applied to join C/C-SiC composites and lithium aluminum silicate（LAS） glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites（1.75 g/cm3） with a CVD-SiC coating to the C/C-SiC composites with a low density（1.48 g/cm3）.The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.
基金supported by the National Natu-ral Science Foundations of China(Nos.51727804,52130205,and 91860203)the National Key R&D Program of China(No.2021YFA0715803)The authors also thank the Analytical&Testing Center of Northwestern Polytechnical University for the characteri-zation of our samples.
文摘Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,the mechanical denudation of the sample only containing acicular crystals and the coating spallation caused by superfluous gaseous products of the sample with the sublayer composed of nanocrystals both indicate their inferior anti-ablation properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.
基金Supported by the National Natural Science Foundation of China under Grant (90716024)the "111" Project under Grant (08040)
文摘A SiC whisker-toughened MoSi2-SiC-Si coating was prepared on carbon/carbon (C/C) composites surface by a two-step technique of slurry and pack cementation, and the effects of thermal shock and oxidation on the mechanical property of the coated C/C were studied. The flexural strength of C/C composites was improved by 6.8% after coated by SiC whisker-toughened MoSi2-SiC-Si. After thermal cycle between 1773 K and room temperature in air for 10 times, the mass loss of the coated sample was 5.08% and the percentage of remaining strength was 81.97%. After oxidation at 1773K in air for 60 min, the mass loss of the coated sample was 2.57% and the percentage of remaining strength was 89.63%. The decrease of the flexural strength during the thermal cycle and oxidation tests was primarily due to the oxidation of C/C substrate resulting from the cracking of coating.
基金supported by the National Natural Science Foundation of China(Grant Nos.51072166 and 51472202)by the Program of Introducing Talents of Discipline to University(Grant No.B08040)
文摘C/C-HfC-SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in the heat flux of 2.38 MW/m2 （HF-L） and 4.18 MW/m2 （HF-H） for 60 s. The mechanical denudation in 4.18 MW/m2 （HF-H） was higher than that in 2.38 MW/m2 （HF-L）, while the results indicated that the composites had a similar and good ablation property under two different flame conditions. C/C- HfC-SiC composites can adapt the heat flux from 2.38 MW/m2 to 4.18 MW/m2. The Hf02 was not melted completely in the heat flux of 2.38 MW/m2 （HF-L）. So, both Hf02 and Si02 layers acted as an effective barrier to the transfer of heat and oxidative gases into the underlying carbon substrate. SiO2 was severely consumed in 4.18 MW/m2 （HF-H）, where the HfO2 molten layer played a more important role in protecting the inner composite.
基金supported by the National "973"Project under grant No. 2006CB600908
文摘A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.
基金supported by the National Natural Science Foundation of China(Grant No.51909219)the National Key Research and Development Program of China(Grant No.2016YFC0301300)+1 种基金Fundamental Research Funds for the Central Universities(Grant No.3102019JC006)China Postdoctoral Science Foundation(Grand No.2020M673492)。
文摘The initial geometric imperfection is one of the primary factors affecting the buckling behaviors of composite cylindrical shells under hydrostatic pressure.In this study,ovality and thickness variations as two representative types of the geometric imperfections are considered.After measuring the geometric imperfections,a typical carbon fiber reinforced polymers(CFRP)cylindrical shell is tested to obtain the buckling pressure.The buckling behaviors of the shell sample are analyzed in combination with the strain responses.By using the nonlinear numerical analysis,the buckling shapes of the CFRP cylinder shells with different combinations of ovality and thickness variation are firstly discussed.The rules of influence of such imperfections on the buckling pressure are then obtained by nonlinear regression method.Finally,an empirical formula is proposed to predict the buckling pressure of the composite cylinder shells,and the calculated results from the formula are in good agreement with the numerical results.
基金supported by the “111” Project of China(B08040)the National Natural Science Foundation of China(Grant Nos.51521061 and 51472203)
文摘High-purity carbon nanotubes （CNTs） with different orientation and lengths were grafted on carbon fibers （CFs） in woven fabrics by using double injection chemical vapor deposition and adjusting the growth temperature. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman investigations reveal that the grafted CNTs change from being predominantly aligned and uniform in di- ameter to absolutely disordered and variable in diameter, whilst they show significantly increased crystallinity, as the growth temperature is increased from 730 ~C to 870 ~C. In tensile tests of fiber bundles, much more strength degradation of CFs was observed after the growth process at higher temperature than that at lower temperature. These hybrid preforms produced at different growth temperatures were used to reinforce carbon/carbon （C/C） composites. An increment of 34.4% in out-of-plane compressive strength （OCS） was obtained for the composites containing CNTs grown at 730℃, while the OCS increment exhibits an obvious decrease with increasing the growth temperature. Compared with the higher growth temperature, the lower temperature contributes to the decrease in the strength loss of reinforcing fibers and meanwhile the growth of large extending length of CNTs, which can provide long reinforcement to the pyrocarbon matrix, and thus increase the compressive strength better.
基金financially supported by the National Natural Science Foundation of China(Nos.51221001 and 51272213)the Author of National Excellent Doctoral Dissertation of China(No.201036),the ‘‘111’’ project of China (No.B08040)National Basic Research program of China (No.2011CB605806)
文摘C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of the composites were analyzed by scanning electron microscopy and X-ray diffraction. The ablation resistance of the composites was evaluated under 3,000 °C oxyacetylene torch. After ablation for 120 s, the composites exhibit good ablation properties with the linear and mass ablation rates of 9.1 9 10-4mm/s and 1.30 9 10-3g/s, which are far lower than those of the C/C–SiC composites. The excellent ablative property of the C/C–SiC–HfC composites is resulted from the formation of HfO2 molten layer on the surface of the composites, which could play a positive role in reducing heat transfer and preventing oxygen transport to the underlying carbon substrate.
基金supported by the National Natural Science Foundation of China (Nos. 51472203, 51575447, 51521061)
文摘Carbon fiber reinforced AZ91 D matrix composites with pyrolytic（PyC） coating deposited on fiber surface（PyC-Cf/AZ91 D composites） have been fabricated by Liquid-solid extrusion following vacuum pressure infiltration technique（LSEVI）. Interfacial microstructure and failure behavior of the composites were investigated. Instead of interfacial reaction products, block-shaped interfacial precipitates Mg（17） Al（12） were detected at the interface, which indicates that interfacial reaction was restrained by LSEVI and PyC coating. Nano-MgO was detected at the interface. Interfacial failure behavior of the PyC-Cf/AZ91 D composites,which was the failure between PyC coating and AZ91 D alloy due to the mismatch of thermal expansion and relatively poor bonding, was proposed. Fracture surface of the PyC-Cf/AZ91 D composites was characterized by fibers pulling-out tests. PyC coating served not only as protection to the fibers, but also an adjustment of the interface of the composites.
基金supported by the National Natural Sci-ence Foundation of China under grant Nos. 50802075 and90716024, the "111" Project, China under grant No.08040.
文摘Si-SiC coating was prepared on the surface of carbon/carbon （C/C） composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between !773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.
