Ceramic matrix composites (CMCs) are the preferred materials for solving advanced aerospace high-temperature structural components;it has the comprehensive advantages of higher temperature (~1500˚C) and low density. I...Ceramic matrix composites (CMCs) are the preferred materials for solving advanced aerospace high-temperature structural components;it has the comprehensive advantages of higher temperature (~1500˚C) and low density. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso-architecture and inhere defects. In this paper, the in-plane tensile mechanical behavior of a plain-woven SiCf/SiC composite at room and elevated temperatures was investigated, and the factors affecting the tensile strength of the material were discussed in depth. The results show that the tensile modulus and strength of SiCf/SiC composites at high temperature are lower, but the fracture strain increases and the toughness of the composites is enhanced;the stitching holes significantly weaken the tensile strength of the material, resulting in the material is easy to break at the cross-section with stitching holes.展开更多
To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducte...To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducted by using 7.62 mm armor piercing incendiary(API).Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.展开更多
We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surf...We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.展开更多
Si C nanowires are excellent high-temperature electromagnetic wave (EMW) absorbing materials. However, their polymer matrix composites are difficult to work at temperatures above 300℃, while their ceramic matrix comp...Si C nanowires are excellent high-temperature electromagnetic wave (EMW) absorbing materials. However, their polymer matrix composites are difficult to work at temperatures above 300℃, while their ceramic matrix composites must be prepared above 1000℃ in an inert atmosphere. Thus, for addressing the abovementioned problems, SiC/low-melting-point glass composites were well designed and prepared at 580℃ in an air atmosphere. Based on the X-ray diffraction results, SiC nanowires were not oxidized during air atmosphere sintering because of the low sintering temperature. Additionally, SiC nanowires were uniformly distributed in the glass matrix material. The composites exhibited good mechanical and EMW absorption properties. As the filling ratio of SiC nanowires increased from 5wt%to 20wt%, the Vickers hardness and flexural strength of the composite reached HV 564 and 213 MPa, which were improved by 27.7%and 72.8%, respectively, compared with the low-melting-point glass. Meanwhile, the dielectric loss and EMW absorption ability of SiC nanowires at 8.2–12.4 GHz were also gradually improved. The dielectric loss ability of low-melting-point glass was close to 0. However, when the filling ratio of SiC nanowires was 20wt%, the composite showed a minimum reflection loss (RL) of-20.2 dB and an effective absorption (RL≤-10 dB) bandwidth of2.3 GHz at an absorber layer thickness of 2.3 mm. The synergistic effect of polarization loss and conductivity loss in SiC nanowires was responsible for this improvement.展开更多
This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC pro...This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))展开更多
SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum ...SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.展开更多
A novel Y_(3)Si_(2)C_(2)material was synthesized at a relatively low temperature(900℃)using a molten salt method for the first time,and subsequently used as the joining material for carbon fiber reinforced SiC(Cf/SiC...A novel Y_(3)Si_(2)C_(2)material was synthesized at a relatively low temperature(900℃)using a molten salt method for the first time,and subsequently used as the joining material for carbon fiber reinforced SiC(Cf/SiC)composites.The sound near-seamless joints with no obvious remaining interlayer were obtained at 1600℃using an electric field-assisted sintering technique(FAST).During joining,a liquid phase was formed by the eutectic reaction among Y_(3)Si_(2)C_(2),γ(Y–C)phase,and SiC,followed by the precipitation of SiC particles.The presence of the liquid promoted the sintering of newly formed SiC particles,leading to their complete consolidation with the Cf/SiC matrix.On the other hand,the excess of the liquid was pushed away from the joining area under the effect of a uniaxial pressure of 30 MPa,leading to the formation of the near-seamless joints.The highest shear strength(Ä)of 17.2±2.9 MPa was obtained after being joined at 1600℃for 10 min.The failure of the joints occurred in the Cf/SiC matrix,indicating that the interface was stronger than that of the Cf/SiC matrix.The formation of a near-seamless joint minimizes the mismatch of thermal expansion coefficients and also irradiation-induced swelling,suggesting that the proposed joining strategy can be potentially applied to SiC-based ceramic matrix composites(CMCs)for extreme environmental applications.展开更多
Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresse...Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresses in SiCf/Ti2AlNb composites.Two coating systems were comparatively studied,namely C coating and C/Mo duplex-coating.The thermal residual stresses after 1 080 ℃/1 h solution treatment and 800 ℃/20 h ageing treatment in the composites were also analyzed.The experimental results show that Mo coating can decrease thermal residual stress magnitude in the matrix.However,it would increase the thermal residual stresses in the interfacial reaction layer of TiC.The change of radial thermal residual stress in TiC layer is inconspicuous after solid solution and ageing treatment,but the hoop and axial thermal residual stresses increase obviously.However,the heat treatment can obviously reduce hoop and axial thermal residual stresses of the matrix,which is benefit to restrain the initiation and propagation of cracks in the matrix.展开更多
The properties and structures of 3D-Cf/ SiC composites prepared by rapid precursor infiltration pyrolysis process were studied.PCS solution was infiltrated into 3D-carbon fiber perform in vacuum,then these performs we...The properties and structures of 3D-Cf/ SiC composites prepared by rapid precursor infiltration pyrolysis process were studied.PCS solution was infiltrated into 3D-carbon fiber perform in vacuum,then these performs were dried at room temperature and pyrolyzed with three kinds of heating rate,3 900 min,1 500 min and 1 000 min respectively.The distinction of 3D-Cf/SiC samples fabricated at three kinds of heating rate was not obvious.Bending strength of sample at 1 000 min heating rate was 762.5 MPa,and a little better than the others.Three samples at various heating rate had similar micro-graph of fracture surface and fracture toughness.The research results show that mechanics performances of Cf/SiC composites did not decrease when heating rate was properly increased.展开更多
Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity ...Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity and cracks were not observed at weld interfaces of all the joints. Penetration of filler material in to voids and pores existing in the Cf-SiC composites was observed. Average shear strength of 25.7 MPa was achieved for joints of Cf-SiC composites. By incorporation of Cf-SiC(CVD) ground short fibre reinforcement the(ZrB_2-SiC-B_4C-YAG) composite was machinable with tungsten carbide tool. The joint and machined composites were resistance to oxidation and thermal shock when exposed to the oxy-propane flame at 2300℃ for 300s. The combination of(ZrB_2-SiC-B_4C-YAG) and Cf-SiC based composites can be used for making parts like thermal protection system or nozzles for high temperature applications.展开更多
Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing (PP-HP) and precursor impregnation-pyrolysis (PIP), respectively. The effect of fabrication methods on the microstructure an...Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing (PP-HP) and precursor impregnation-pyrolysis (PIP), respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa.m^1/2.展开更多
SiC with fiber-reinforced composites, which are presently considered as the primary structural materials in some fusion reactor conceptual designs, are more attractive and competitive for structural materials in a fus...SiC with fiber-reinforced composites, which are presently considered as the primary structural materials in some fusion reactor conceptual designs, are more attractive and competitive for structural materials in a fusion energy system because of its excellent chemical and mechanical properties such as high fracture toughness, induced-low activation, afterheat under 14MeV neutron irradiation environment at elevated temperature, and good compatibility with coolant and breeder materials. Thus it is important to investigate the research progress of advanced SiC composite, including transmuted helium gas, radiation swelling, radiation effects on mechanical properties, irradiation-enhanced creep, fatigue, physical properties associated with fusion design and their critical issues. This report summarized these results and addressed the major critical issues under irradiation conditions.展开更多
The compression creep deformation of the high volume fraction of SiC particles reinforced AI-Mg-Si composite fabricated by pressure-less infiltration was investigated. The experimental results show that the creep stre...The compression creep deformation of the high volume fraction of SiC particles reinforced AI-Mg-Si composite fabricated by pressure-less infiltration was investigated. The experimental results show that the creep stress exponents are very high at temperatures of 673 K, 723 K and 773 K, and if taking the threshold stress into account, the true stress exponent of minimum creep strain rate is still approximately 5, although the volume fraction of reinforcements is very high. The creep strain rate in the high volume fraction reinforced aluminum alloy matrix composites is controlled by matrix lattice diffusion. It is found that the creep-strengthening effect of high volume fraction of silicon carbide particles is significant, although the particles do not form effective obstacles to dislocation motion.展开更多
文摘Ceramic matrix composites (CMCs) are the preferred materials for solving advanced aerospace high-temperature structural components;it has the comprehensive advantages of higher temperature (~1500˚C) and low density. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso-architecture and inhere defects. In this paper, the in-plane tensile mechanical behavior of a plain-woven SiCf/SiC composite at room and elevated temperatures was investigated, and the factors affecting the tensile strength of the material were discussed in depth. The results show that the tensile modulus and strength of SiCf/SiC composites at high temperature are lower, but the fracture strain increases and the toughness of the composites is enhanced;the stitching holes significantly weaken the tensile strength of the material, resulting in the material is easy to break at the cross-section with stitching holes.
基金Funded by the National Natural Science Foundation of China(No.51271036)
文摘To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducted by using 7.62 mm armor piercing incendiary(API).Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.
基金Supported by Innovation and Technology Fund (No.ITP/045/19AP)Commercial Research&Development (CRD) Funding Supported by Hong Kong Productivity Council (No.10008787)。
文摘We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.
基金financially supported by the National Natural Science Foundation of China (Nos.51702011 and 51572018)the Fundamental Research Funds for the Central Universities of China (No.FRF-TP-20-006A3)the Scientific Research Project of Hunan Province Department of Education,China (No.20B323)。
文摘Si C nanowires are excellent high-temperature electromagnetic wave (EMW) absorbing materials. However, their polymer matrix composites are difficult to work at temperatures above 300℃, while their ceramic matrix composites must be prepared above 1000℃ in an inert atmosphere. Thus, for addressing the abovementioned problems, SiC/low-melting-point glass composites were well designed and prepared at 580℃ in an air atmosphere. Based on the X-ray diffraction results, SiC nanowires were not oxidized during air atmosphere sintering because of the low sintering temperature. Additionally, SiC nanowires were uniformly distributed in the glass matrix material. The composites exhibited good mechanical and EMW absorption properties. As the filling ratio of SiC nanowires increased from 5wt%to 20wt%, the Vickers hardness and flexural strength of the composite reached HV 564 and 213 MPa, which were improved by 27.7%and 72.8%, respectively, compared with the low-melting-point glass. Meanwhile, the dielectric loss and EMW absorption ability of SiC nanowires at 8.2–12.4 GHz were also gradually improved. The dielectric loss ability of low-melting-point glass was close to 0. However, when the filling ratio of SiC nanowires was 20wt%, the composite showed a minimum reflection loss (RL) of-20.2 dB and an effective absorption (RL≤-10 dB) bandwidth of2.3 GHz at an absorber layer thickness of 2.3 mm. The synergistic effect of polarization loss and conductivity loss in SiC nanowires was responsible for this improvement.
基金This work was supported by the National Natural Science Foundation of China(Grant Numbers of U1902220,51674166,51374145,51074106,50674067)the National Key Research and Development Program of China(Grant Number 2016YFB0301001).
文摘This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))
基金Funded by the National Key R&D Program of China(No.2018YFB1501002)。
文摘SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.
基金This study was supported by the National Natural Science Foundation of China(Grant No.11975296)the Natural Science Foundation of Ningbo City(Grant No.2021J199)+3 种基金We would like to recognize the support from the Ningbo 3315 Innovative Teams Program,China(Grant No.2019A-14-C)Peter TATARKO gratefully acknowledges the financial support of the project APVV-17-0328this study was performed as part of the implementation of the project“Building-up Centre for advanced materials application of the Slovak Academy of Sciences”and ITMS project(Grant No.313021T081)supported by the Research&Innovation Operational Programme funded by the ERDF.
文摘A novel Y_(3)Si_(2)C_(2)material was synthesized at a relatively low temperature(900℃)using a molten salt method for the first time,and subsequently used as the joining material for carbon fiber reinforced SiC(Cf/SiC)composites.The sound near-seamless joints with no obvious remaining interlayer were obtained at 1600℃using an electric field-assisted sintering technique(FAST).During joining,a liquid phase was formed by the eutectic reaction among Y_(3)Si_(2)C_(2),γ(Y–C)phase,and SiC,followed by the precipitation of SiC particles.The presence of the liquid promoted the sintering of newly formed SiC particles,leading to their complete consolidation with the Cf/SiC matrix.On the other hand,the excess of the liquid was pushed away from the joining area under the effect of a uniaxial pressure of 30 MPa,leading to the formation of the near-seamless joints.The highest shear strength(Ä)of 17.2±2.9 MPa was obtained after being joined at 1600℃for 10 min.The failure of the joints occurred in the Cf/SiC matrix,indicating that the interface was stronger than that of the Cf/SiC matrix.The formation of a near-seamless joint minimizes the mismatch of thermal expansion coefficients and also irradiation-induced swelling,suggesting that the proposed joining strategy can be potentially applied to SiC-based ceramic matrix composites(CMCs)for extreme environmental applications.
基金Funded by the National Natural Science Foundation of China (No. 51201134)the Key Research Foundation of Yiwu Industrial and Commercial College (No. ZD2020CS414-01)。
文摘Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresses in SiCf/Ti2AlNb composites.Two coating systems were comparatively studied,namely C coating and C/Mo duplex-coating.The thermal residual stresses after 1 080 ℃/1 h solution treatment and 800 ℃/20 h ageing treatment in the composites were also analyzed.The experimental results show that Mo coating can decrease thermal residual stress magnitude in the matrix.However,it would increase the thermal residual stresses in the interfacial reaction layer of TiC.The change of radial thermal residual stress in TiC layer is inconspicuous after solid solution and ageing treatment,but the hoop and axial thermal residual stresses increase obviously.However,the heat treatment can obviously reduce hoop and axial thermal residual stresses of the matrix,which is benefit to restrain the initiation and propagation of cracks in the matrix.
文摘The properties and structures of 3D-Cf/ SiC composites prepared by rapid precursor infiltration pyrolysis process were studied.PCS solution was infiltrated into 3D-carbon fiber perform in vacuum,then these performs were dried at room temperature and pyrolyzed with three kinds of heating rate,3 900 min,1 500 min and 1 000 min respectively.The distinction of 3D-Cf/SiC samples fabricated at three kinds of heating rate was not obvious.Bending strength of sample at 1 000 min heating rate was 762.5 MPa,and a little better than the others.Three samples at various heating rate had similar micro-graph of fracture surface and fracture toughness.The research results show that mechanics performances of Cf/SiC composites did not decrease when heating rate was properly increased.
基金financial support from the Defence Research and Development Organisation, Ministry of Defence, Govt. of India, New Delhi in order to carry out the present study under project DMR-295
文摘Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity and cracks were not observed at weld interfaces of all the joints. Penetration of filler material in to voids and pores existing in the Cf-SiC composites was observed. Average shear strength of 25.7 MPa was achieved for joints of Cf-SiC composites. By incorporation of Cf-SiC(CVD) ground short fibre reinforcement the(ZrB_2-SiC-B_4C-YAG) composite was machinable with tungsten carbide tool. The joint and machined composites were resistance to oxidation and thermal shock when exposed to the oxy-propane flame at 2300℃ for 300s. The combination of(ZrB_2-SiC-B_4C-YAG) and Cf-SiC based composites can be used for making parts like thermal protection system or nozzles for high temperature applications.
基金This research was financially supported by the National Natural Science Foundation of China (No. 50404012)
文摘Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing (PP-HP) and precursor impregnation-pyrolysis (PIP), respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa.m^1/2.
基金The project supported by the 21st COE research program of Kyoto University on the establishment of sustainable energy system
文摘SiC with fiber-reinforced composites, which are presently considered as the primary structural materials in some fusion reactor conceptual designs, are more attractive and competitive for structural materials in a fusion energy system because of its excellent chemical and mechanical properties such as high fracture toughness, induced-low activation, afterheat under 14MeV neutron irradiation environment at elevated temperature, and good compatibility with coolant and breeder materials. Thus it is important to investigate the research progress of advanced SiC composite, including transmuted helium gas, radiation swelling, radiation effects on mechanical properties, irradiation-enhanced creep, fatigue, physical properties associated with fusion design and their critical issues. This report summarized these results and addressed the major critical issues under irradiation conditions.
文摘The compression creep deformation of the high volume fraction of SiC particles reinforced AI-Mg-Si composite fabricated by pressure-less infiltration was investigated. The experimental results show that the creep stress exponents are very high at temperatures of 673 K, 723 K and 773 K, and if taking the threshold stress into account, the true stress exponent of minimum creep strain rate is still approximately 5, although the volume fraction of reinforcements is very high. The creep strain rate in the high volume fraction reinforced aluminum alloy matrix composites is controlled by matrix lattice diffusion. It is found that the creep-strengthening effect of high volume fraction of silicon carbide particles is significant, although the particles do not form effective obstacles to dislocation motion.