Silicon carbide fibers are considered ideal reinforcing materials for ceramic matrix composites due to their excellent mechanical properties and high-temperature performance.Different types of fibers necessitate indiv...Silicon carbide fibers are considered ideal reinforcing materials for ceramic matrix composites due to their excellent mechanical properties and high-temperature performance.Different types of fibers necessitate individual investigation due to variations in their composition and fabrication processes.This study presents a comprehensive investigation into evolution of the mechanical properties,surface microstructure,and composition of Shicolon-Ⅱ fibers subjected to argon heat treatment at temperatures ranging from 1300℃to 1700℃.The Shicolon-Ⅱ fibers are composed of small-sized β-SiC grains,SiC_(x)O_(y) amorphous phase,and a minor amount of graphite microcrystals.Following treatment in an argon atmosphere at 1300℃,the fibers maintain a monofilament tensile strength of 3.620 GPa,corresponding to a retention of 98.32%.This strength diminishes to 2.875 GPa,equating to a retention of 78.08%,after treatment at 1500℃.The reduction in mechanical properties of the fibers can be ascribed to the decomposition of the amorphous phase and the growth of β-SiC grains.Furthermore,creep resistance is an essential factor influencing the long-term performance of composite materials.After treatment at temperatures above 1400℃,the high-temperature creep resistance of the fibers is significantly enhanced due to growth of β-SiC grains.This study offers valuable theoretical insights into high-temperature applications of second-generation fibers,contributing to an enhanced understanding of their performance under extreme conditions.展开更多
C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl com...C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl composites were also prepared under the same processing condition for comparision. Both kinds of the composites were thermally exposed in vacuum at 800 and 900℃ for different durations in order to study thermal stability of the interfacial zone. With the aids of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）, the interracial microstructures of the composites were investigated. The results reveal that, although adding the Mo coating, the interfacial reaction product of the SiCf/C/Mo/TiAl composite is the same with that of the SiCf/C/TiA1 composite, which is TiC/Ti2AlC between the coating and the matrix. However, C/Mo duplex coating is more efficient in hindering interfacial reaction than C single coating at 900 ℃ and below. In addition, a new layer of interfacial reaction product was found between Ti2AlC and the matrix after 900 ℃, 200 h thermal exposure, which is rich in V and close to the chemical composition of B2 phase.展开更多
Compared with the first and second generations SiC fibers, the third generation SiC fibers have obvious improvement in heat-resistance, oxidation-resistance and creep-resistance, which promote the development of SiCf/...Compared with the first and second generations SiC fibers, the third generation SiC fibers have obvious improvement in heat-resistance, oxidation-resistance and creep-resistance, which promote the development of SiCf/SiC composite materials. Therefore, the third generation SiC fibers have more advantages and broader prospects in engineering applications. In this paper, the fabrication and properties of the third generation SiC fibers are compared and discussed. The preparation processes of the third generation SiC fibers reinforced SiC matrix composites and their application in aeroengine and nuclear energy fields are summarized, while their future development is prospected as well.展开更多
Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with ...Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with SiC fiber addition were prepared via stereolithography,and the influence of SiC fiber content on mechanical properties of the obtained silica-based ceramics was investigated.With the increase of SiC fiber content,linear shrinkage gradually decreased,while room temperature flexural strength and high temperature flexural strength first increased and then decreased.As SiC fiber content increased to 4.0 wt%,linear shrinkage was reduced to 0.62%resulting from the oxidation of SiC.Furthermore,room temperature flexural strength was improved from 11.79 MPa to 23.83 MPa and high temperature flexural strength was enhanced from 15.64 MPa to 34.62 MPa with 4.0 wt%SiC fiber addition due to the reinforcement of fibers and the enhancedβ-cristobalite content,which meets the need of ceramic cores.Therefore,it demonstrates the capability of fabricating high-performance and high-precision silica-based ceramic cores reinforced by SiC fibers via stereolithography for rapid manufacturing of hollow blades.展开更多
In this work,a modified approach for preparing CVD SiC fiber-reinforced superalloy matrix composites was rationally developed.The composites were fabricated by vacuum hot pressing(VHP)process using precursor wires coa...In this work,a modified approach for preparing CVD SiC fiber-reinforced superalloy matrix composites was rationally developed.The composites were fabricated by vacuum hot pressing(VHP)process using precursor wires coated with(Al+Al2O3)diffusion barrier layers and GH4169 superalloy coatings.BNi-7 brazing filler metals were introduced on the surface of precursor wires in order to decrease the temperature of the VHP process.It was found that the VHP temperature was reduced by about 100℃,and the melting,diffusion,nucleation and growth processes of BNi-7 fillers at 900?C motivated the recrystallization and plastic flow of the matrix under the increasing pressure,thereby a compact composite composed of intact SiC fibers and fine equiaxial grain structure superalloy matrix was achieved.Meanwhile,the elements were distributed homogeneously among the fibers in the composite and no interfacial reactions occurred.This method provides a new insight for designing and manufacturing high-quality composites in practical engineering.展开更多
In this work,the effects of Cr and Al contents on the preparation of SiC fiber-reinforced NiCrAl alloy matrix composites(SiCf/Ni-20Cr-5Al,SiCf/Ni-15Cr-5Al,SiCf/Ni-10Cr-5Al and SiCf/Ni-10Cr-3Al)were thoroughly discusse...In this work,the effects of Cr and Al contents on the preparation of SiC fiber-reinforced NiCrAl alloy matrix composites(SiCf/Ni-20Cr-5Al,SiCf/Ni-15Cr-5Al,SiCf/Ni-10Cr-5Al and SiCf/Ni-10Cr-3Al)were thoroughly discussed.The composites were prepared by vacuum hot pressing process using matrix-coated fibers.It was found that Cr solute atoms played a significant role in retarding the recrystallization of NiCrAl alloy matrix,and the Al elements in the form of γ'-Ni3Al phase had a suppression effect on the plastic flow of the matrix.Therefore,the reduction in Cr and Al contents was conductive to the recrystallization and plastic flow of NiCrAl alloy matrix,thereby reduced the size and number of micro-voids in the composite.In addition,this work provides some guidance for designing and manufacturing reasonable SiC fiber-reinforced Ni alloy matrix composites.展开更多
Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation ...Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.展开更多
Microstructure of SiC fiber manufactured by chemical vapor deposition （CVD） onto tungsten （W） wire core was investigated by analytical electron microscopy （AEM）. The results reveal that the fiber consists of W c...Microstructure of SiC fiber manufactured by chemical vapor deposition （CVD） onto tungsten （W） wire core was investigated by analytical electron microscopy （AEM）. The results reveal that the fiber consists of W core, SiC sheath and C-coating. SiC sheath could be subdivided into two parts according to whether containing C rich stripe, or not. An emphasis was put on W/SiC interfacial reaction products and the transition zone between sub-layers in SiC sheath. The W/SiC interface consists of three layers of reaction production, namely, W2C, W5Si3 and WC. And there are amounts of facet faults existing in （100） face of WC crystalline and two classes of stack faults in WC have been revealed. The formation essence of different sublayers in SiC sheath was also discussed.展开更多
SiC fibers were irradiated by 414.4-MeV^(112)Sn^(27.3+)ions to different fluences(5.0×10^(12),6.0×10^(13),1.6×10^(14),and 1.92×10^(15)ions/cm^(2)).^(112)Sn^(27.3+)deposited its energy mainly via el...SiC fibers were irradiated by 414.4-MeV^(112)Sn^(27.3+)ions to different fluences(5.0×10^(12),6.0×10^(13),1.6×10^(14),and 1.92×10^(15)ions/cm^(2)).^(112)Sn^(27.3+)deposited its energy mainly via electron energy loss and passed through the SiC fiber.Then,the mechanical properties and surface characteristics of fibers were studied using a specific single filament tensile test and field emission scanning electron microscopy.Results revealed that the carbon concentration on the fiber surface increased while the silicon concentration decreased.Moreover,the addition of oxygen was found to correlate with an increase in ion fluence.Meanwhile,the fiber surface morphology of the least fluence(5.0×10^(12)ions/cm^(2))irradiated specimen displayed no obvious changes and its diameter was slightly reduced.With successive increases of ion fluence,large grains/bubbles on the fiber surface first appeared and then disappeared,and the diameter of fibers evidently increased.Moreover,at the highest fluence(1.92×10^(15)Sn ions/cm^(2))irradiated specimen,some fibers were brittle fractured.As a result,the mean tensile strength and the average elastic modulus of the fibers generally decreased with respect to the ion fluence.The degradation mechanisms of mechanical properties of SiC fibers under irradiation are discussed in detail.展开更多
A method of preparing continuous（Al＋Al2O3）-coated SiC fiber reinforced nickel matrix composite was presented,in which the diffusion between SiC fiber and nickel matrix could be prevented.Magnetron sputtering is use...A method of preparing continuous（Al＋Al2O3）-coated SiC fiber reinforced nickel matrix composite was presented,in which the diffusion between SiC fiber and nickel matrix could be prevented.Magnetron sputtering is used to deposit Ni coating on the surface of the（Al＋Al2O3）-coated SiC fiber in preparation of the precursor wires.It is shown that the deposited Ni coating combines well with the（Al＋Al2O3） coating and has little negative effect on the tensile strength of（Al＋Al2O3）-coated SiC fiber.Solid-state diffusion bonding process is employed to prepare the（Al＋Al2O3）-coated SiC fiber reinforced nickel matrix with 37% fibers in volume.The solid-state diffusion bonding process is optimized and the optimum parameters are temperature of 870,pressure of 50 MPa and holding time of 2 h.Under this condition,the precursor wires can diffuse well,composite of full density can be formed and the（Al＋Al2O3） coating is effective to restrict the reaction between SiC fiber and nickel matrix.展开更多
In SiC（f）/Ti-6Al-4V composites, the microstructure of the matrix close to the fiber was different from that of the fiber-less material. Microstructure observations show that a layer of fine grains was located adjace...In SiC（f）/Ti-6Al-4V composites, the microstructure of the matrix close to the fiber was different from that of the fiber-less material. Microstructure observations show that a layer of fine grains was located adjacent to the fiber, and more dislocations and faults were found in this region. Higher recrystallization nucleation rate due to the undeformed SiC fiber and thermal residual stress induced during cooling from the fabrication temperature caused the microstructural changes of the matrix. Hardness measurement indicates that the matrix in the fiber neighborhood was strengthened, and the strengthening effect decreased with distance away from the fiber.展开更多
In order to explore the effect of high-temperature annealing on the mechanical performances and microstructures of different oxygen SiC fibers, two types of silicon carbide（SiC）-based fibers, specified as XD-SiC fib...In order to explore the effect of high-temperature annealing on the mechanical performances and microstructures of different oxygen SiC fibers, two types of silicon carbide（SiC）-based fibers, specified as XD-SiC fibers（low oxygen） and Nicalon-201 fibers（high oxygen）, were annealed in Ar for 1 h at 800 ℃, 1 000 and 1 200 ℃, respectively. Mechanical properties of these fibers were characterized via a monofilament tensile method, with observation of the damaged monofilament by SEM. Also, the effects of annealing on the microstructure and chemical compositions of the fibers were studied. The experimental results indicated that the tensile strength decreased with the increase of annealing temperatures,after annealing-treatment at 1200℃, XD-SiC fibers remained 84% of its original strength, while Nicalon-201 fibers remained only 58% of its original strength. Crystallization and chemical composition of the fibers are the dominating factors for their mechanical performance at high temperatures. The microstructure changes of XD-SiC fibers are mainly composed of the growth of β-SiC, for Nicalon-201 fibers, evaporation of gases is the main change for microstructure.展开更多
The tensile strength of CVD SiC fiber was remarkably improved by electrochemical surface treatment. SEM analyses reveal that AC current treatment could form a more compact and complete SiO2 layer than DC current on th...The tensile strength of CVD SiC fiber was remarkably improved by electrochemical surface treatment. SEM analyses reveal that AC current treatment could form a more compact and complete SiO2 layer than DC current on the surface of the SiC fiber, which was beneficial to the improvement of tensile strength. It was also verified that AC current was more effective for producing high performance SiC fiber with SiO2 surface layer than DC current. The frequency is a sensitive parameter for the process; but the signals of input current had relatively small effect on the tensile strength of SiC fiber. A further discussion for this phenomenon was completed. The proposed operational parameters are 0.3 A, 5 kHz of sine wave and 91 m/h of the receiving rate respectively.展开更多
In this paper, the creep resistance of 2D braided SiC/SiC composites was studied under the stress conditions of 120MPa and 140MPa at 1200℃. The creep curve is obtained through the experiment. Through the analysis and...In this paper, the creep resistance of 2D braided SiC/SiC composites was studied under the stress conditions of 120MPa and 140MPa at 1200℃. The creep curve is obtained through the experiment. Through the analysis and calculation of the creep curve, the material has excellent creep resistance in the environment of 1200℃ and 120MPa, and the creep resistance is reduced due to higher stress in the environment of 1200℃ and 140MPa. Through calculation, the average creep rate of the materials under the two stresses is (5±1) × 10-8/s, (1.6±0.6) × 10-7/s respectively, and the creep rate is increased by 3.2 times under 140MPa stress.展开更多
Raman spectroscopy was used to measure Raman spectra of the inner SiC fibers and surface C-rich layers of SiC fibers, composite precursors and SiCf/Ni-Cr-Al composites. The residual stresses of the inner SiC fibers an...Raman spectroscopy was used to measure Raman spectra of the inner SiC fibers and surface C-rich layers of SiC fibers, composite precursors and SiCf/Ni-Cr-Al composites. The residual stresses of the inner SiC fibers and surface C-rich layers were calculated, and the effect of the(Al + Al_2O_3) diffusion barrier layer on the interfacial residual stress in the composites was analyzed in combination with the interface microstructure and energy disperse spectroscopy(EDS) elements lining maps. The results show that the existence of(Al + Al_2O_3) diffusion barrier improves the compatibility of the SiCf/Ni-Cr-Al interface,inhibits the adverse interfacial reaction, and relieves the residual stress inside SiC fibers and at the interface of composite material. Heat treatment can reduce the residual stress at the interface. As the heat treatment time increases, the residual stress at the interface decreases.展开更多
Three types of SiC fibers with different tensile strength were employed to prepare unidirectional titanium matrix composites. The strengths of the original SiC fibers and extracted fibers from the composites were meas...Three types of SiC fibers with different tensile strength were employed to prepare unidirectional titanium matrix composites. The strengths of the original SiC fibers and extracted fibers from the composites were measured. The results show that the mechanical properties of fibers are greatly damaged by the consolidation processing of the composite. The strength data of the extracted fibers are used to predict the strength of the composites according to two theoretic models. The Globe Load-Sharing(GLS) model overestimates the strength of the composites. If the Local Load-Sharing(LLS) model assumes that failure occurs after the formation of a cluster with three broken fibers, the model can predict the strength of the composites exactly.展开更多
Air-curing is usually applied to the polymer-derived SiC fibers and, as a result, oxygen is embedded to the material. An effective relationship between oxygen content of the SiC fibers and mass gain of their precursor...Air-curing is usually applied to the polymer-derived SiC fibers and, as a result, oxygen is embedded to the material. An effective relationship between oxygen content of the SiC fibers and mass gain of their precursor fibers was established. Results also showed that oxygen content has a great influence on the mechanical properties and excellent tensile strength is usually obtained at the oxygen content of 12%～13%, similar to the density of SiC fibers. Oxygen content has a positive effect on the ceramic yield, and thus, is good to the density and tensile strength; while, oxygen content is also negative to volume content of SiC phase and crystallization of the SiC fibers, and thus, detrimental to the density and tensile strength. Both of the two effects result in the peak behavior of the tensile strength of SiC fibers.展开更多
A new SiC fiber was prepared by the pyrolysis of polycarbosilane(PCS)fiber cured with unsaturated hydrocarbons.The fiber,with oxygen content of 4-6 wt%,offers high tensile strength of 2.5-2.8 GPa.The electrical resist...A new SiC fiber was prepared by the pyrolysis of polycarbosilane(PCS)fiber cured with unsaturated hydrocarbons.The fiber,with oxygen content of 4-6 wt%,offers high tensile strength of 2.5-2.8 GPa.The electrical resistivity of the fiber is only about 0.5Ω·cm,much lower than general SiC fiber obtained from traditional air curing process.Degradation of mechanical property in argon and air at high temperature is retarded by 200-300℃with respect to the Nicalon NL-202 fiber.The low electrical resistivity of the fiber exhibits excellent thermal stability,it almost remains 0.4-0.8Ω·cm after thermal exposure test from the room temperature to 1600℃in argon.The low electrical resistivity mainly attribute to an excess carbon layer which is about 50 nm in the circular outer part.展开更多
基金National Natural Science Foundation of China(52172108)National Key R&D Program of China(2022YFB3707700)Strategic Priority Research Program of the Chinese Academy of Sciences(XDC0144005)。
文摘Silicon carbide fibers are considered ideal reinforcing materials for ceramic matrix composites due to their excellent mechanical properties and high-temperature performance.Different types of fibers necessitate individual investigation due to variations in their composition and fabrication processes.This study presents a comprehensive investigation into evolution of the mechanical properties,surface microstructure,and composition of Shicolon-Ⅱ fibers subjected to argon heat treatment at temperatures ranging from 1300℃to 1700℃.The Shicolon-Ⅱ fibers are composed of small-sized β-SiC grains,SiC_(x)O_(y) amorphous phase,and a minor amount of graphite microcrystals.Following treatment in an argon atmosphere at 1300℃,the fibers maintain a monofilament tensile strength of 3.620 GPa,corresponding to a retention of 98.32%.This strength diminishes to 2.875 GPa,equating to a retention of 78.08%,after treatment at 1500℃.The reduction in mechanical properties of the fibers can be ascribed to the decomposition of the amorphous phase and the growth of β-SiC grains.Furthermore,creep resistance is an essential factor influencing the long-term performance of composite materials.After treatment at temperatures above 1400℃,the high-temperature creep resistance of the fibers is significantly enhanced due to growth of β-SiC grains.This study offers valuable theoretical insights into high-temperature applications of second-generation fibers,contributing to an enhanced understanding of their performance under extreme conditions.
基金Projects(51201134,51271147)supported by the National Natural Science Foundation of ChinaProject(2015JM5181)supported by the Natural Science Foundation of Shaanxi Province,China+1 种基金Project(115-QP-2014)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject(3102014JCQ01023)supported by the Fundamental Research Funds for the Central Universities,China
文摘C/Mo duplex coating interfacially modified SiC fiber-reinforced γ-TiAl matrix composite （SiCf/C/Mo/γ-TiA1） was prepared by foil-fiber-foil method to investigate its interfacial modification effect. SiCf/C/TiAl composites were also prepared under the same processing condition for comparision. Both kinds of the composites were thermally exposed in vacuum at 800 and 900℃ for different durations in order to study thermal stability of the interfacial zone. With the aids of scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）, the interracial microstructures of the composites were investigated. The results reveal that, although adding the Mo coating, the interfacial reaction product of the SiCf/C/Mo/TiAl composite is the same with that of the SiCf/C/TiA1 composite, which is TiC/Ti2AlC between the coating and the matrix. However, C/Mo duplex coating is more efficient in hindering interfacial reaction than C single coating at 900 ℃ and below. In addition, a new layer of interfacial reaction product was found between Ti2AlC and the matrix after 900 ℃, 200 h thermal exposure, which is rich in V and close to the chemical composition of B2 phase.
文摘Compared with the first and second generations SiC fibers, the third generation SiC fibers have obvious improvement in heat-resistance, oxidation-resistance and creep-resistance, which promote the development of SiCf/SiC composite materials. Therefore, the third generation SiC fibers have more advantages and broader prospects in engineering applications. In this paper, the fabrication and properties of the third generation SiC fibers are compared and discussed. The preparation processes of the third generation SiC fibers reinforced SiC matrix composites and their application in aeroengine and nuclear energy fields are summarized, while their future development is prospected as well.
基金supported by National Science and Technology Major Project(no.2017-Ⅶ-0008-0102)National Natural Science Foundation of China(no.51975230)Fundamental Research Funds for the Central Universities(nos.2019kfy XMPY020,2020kfy FPZX003,2018KFYYXJJ030,2019kfy XKJC011)。
文摘Silica-based ceramic cores have been widely used to fabricate aero-engine hollow blades due to their moderate high temperature mechanical properties and excellent leachability.In this study,silica-based ceramics with SiC fiber addition were prepared via stereolithography,and the influence of SiC fiber content on mechanical properties of the obtained silica-based ceramics was investigated.With the increase of SiC fiber content,linear shrinkage gradually decreased,while room temperature flexural strength and high temperature flexural strength first increased and then decreased.As SiC fiber content increased to 4.0 wt%,linear shrinkage was reduced to 0.62%resulting from the oxidation of SiC.Furthermore,room temperature flexural strength was improved from 11.79 MPa to 23.83 MPa and high temperature flexural strength was enhanced from 15.64 MPa to 34.62 MPa with 4.0 wt%SiC fiber addition due to the reinforcement of fibers and the enhancedβ-cristobalite content,which meets the need of ceramic cores.Therefore,it demonstrates the capability of fabricating high-performance and high-precision silica-based ceramic cores reinforced by SiC fibers via stereolithography for rapid manufacturing of hollow blades.
基金financially supported by the National Natural Science Foundation of China(No.51371170)。
文摘In this work,a modified approach for preparing CVD SiC fiber-reinforced superalloy matrix composites was rationally developed.The composites were fabricated by vacuum hot pressing(VHP)process using precursor wires coated with(Al+Al2O3)diffusion barrier layers and GH4169 superalloy coatings.BNi-7 brazing filler metals were introduced on the surface of precursor wires in order to decrease the temperature of the VHP process.It was found that the VHP temperature was reduced by about 100℃,and the melting,diffusion,nucleation and growth processes of BNi-7 fillers at 900?C motivated the recrystallization and plastic flow of the matrix under the increasing pressure,thereby a compact composite composed of intact SiC fibers and fine equiaxial grain structure superalloy matrix was achieved.Meanwhile,the elements were distributed homogeneously among the fibers in the composite and no interfacial reactions occurred.This method provides a new insight for designing and manufacturing high-quality composites in practical engineering.
基金financially supported by the National Natural Science Foundation of China(No.51371170)。
文摘In this work,the effects of Cr and Al contents on the preparation of SiC fiber-reinforced NiCrAl alloy matrix composites(SiCf/Ni-20Cr-5Al,SiCf/Ni-15Cr-5Al,SiCf/Ni-10Cr-5Al and SiCf/Ni-10Cr-3Al)were thoroughly discussed.The composites were prepared by vacuum hot pressing process using matrix-coated fibers.It was found that Cr solute atoms played a significant role in retarding the recrystallization of NiCrAl alloy matrix,and the Al elements in the form of γ'-Ni3Al phase had a suppression effect on the plastic flow of the matrix.Therefore,the reduction in Cr and Al contents was conductive to the recrystallization and plastic flow of NiCrAl alloy matrix,thereby reduced the size and number of micro-voids in the composite.In addition,this work provides some guidance for designing and manufacturing reasonable SiC fiber-reinforced Ni alloy matrix composites.
基金The authors wish to thank the Royal Society, UK, and the Chinese Academy of Sciences for sponsoring a joint project-Grant No.761. The nitridation of the SiC fiber (Sigma SM1240) was carried out at QM, University of London, UK. Supply of the SiC fiber by
文摘Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.
文摘Microstructure of SiC fiber manufactured by chemical vapor deposition （CVD） onto tungsten （W） wire core was investigated by analytical electron microscopy （AEM）. The results reveal that the fiber consists of W core, SiC sheath and C-coating. SiC sheath could be subdivided into two parts according to whether containing C rich stripe, or not. An emphasis was put on W/SiC interfacial reaction products and the transition zone between sub-layers in SiC sheath. The W/SiC interface consists of three layers of reaction production, namely, W2C, W5Si3 and WC. And there are amounts of facet faults existing in （100） face of WC crystalline and two classes of stack faults in WC have been revealed. The formation essence of different sublayers in SiC sheath was also discussed.
基金the National Natural Science Foundation of China(Nos.11675231,91426304)the Sichuan Science and Technology Program(No.2022YFG0263)the Scientific Research Starting Foundation for talents(Nos.21zx7109,21zx7110).
文摘SiC fibers were irradiated by 414.4-MeV^(112)Sn^(27.3+)ions to different fluences(5.0×10^(12),6.0×10^(13),1.6×10^(14),and 1.92×10^(15)ions/cm^(2)).^(112)Sn^(27.3+)deposited its energy mainly via electron energy loss and passed through the SiC fiber.Then,the mechanical properties and surface characteristics of fibers were studied using a specific single filament tensile test and field emission scanning electron microscopy.Results revealed that the carbon concentration on the fiber surface increased while the silicon concentration decreased.Moreover,the addition of oxygen was found to correlate with an increase in ion fluence.Meanwhile,the fiber surface morphology of the least fluence(5.0×10^(12)ions/cm^(2))irradiated specimen displayed no obvious changes and its diameter was slightly reduced.With successive increases of ion fluence,large grains/bubbles on the fiber surface first appeared and then disappeared,and the diameter of fibers evidently increased.Moreover,at the highest fluence(1.92×10^(15)Sn ions/cm^(2))irradiated specimen,some fibers were brittle fractured.As a result,the mean tensile strength and the average elastic modulus of the fibers generally decreased with respect to the ion fluence.The degradation mechanisms of mechanical properties of SiC fibers under irradiation are discussed in detail.
文摘A method of preparing continuous（Al＋Al2O3）-coated SiC fiber reinforced nickel matrix composite was presented,in which the diffusion between SiC fiber and nickel matrix could be prevented.Magnetron sputtering is used to deposit Ni coating on the surface of the（Al＋Al2O3）-coated SiC fiber in preparation of the precursor wires.It is shown that the deposited Ni coating combines well with the（Al＋Al2O3） coating and has little negative effect on the tensile strength of（Al＋Al2O3）-coated SiC fiber.Solid-state diffusion bonding process is employed to prepare the（Al＋Al2O3）-coated SiC fiber reinforced nickel matrix with 37% fibers in volume.The solid-state diffusion bonding process is optimized and the optimum parameters are temperature of 870,pressure of 50 MPa and holding time of 2 h.Under this condition,the precursor wires can diffuse well,composite of full density can be formed and the（Al＋Al2O3） coating is effective to restrict the reaction between SiC fiber and nickel matrix.
文摘In SiC（f）/Ti-6Al-4V composites, the microstructure of the matrix close to the fiber was different from that of the fiber-less material. Microstructure observations show that a layer of fine grains was located adjacent to the fiber, and more dislocations and faults were found in this region. Higher recrystallization nucleation rate due to the undeformed SiC fiber and thermal residual stress induced during cooling from the fabrication temperature caused the microstructural changes of the matrix. Hardness measurement indicates that the matrix in the fiber neighborhood was strengthened, and the strengthening effect decreased with distance away from the fiber.
文摘In order to explore the effect of high-temperature annealing on the mechanical performances and microstructures of different oxygen SiC fibers, two types of silicon carbide（SiC）-based fibers, specified as XD-SiC fibers（low oxygen） and Nicalon-201 fibers（high oxygen）, were annealed in Ar for 1 h at 800 ℃, 1 000 and 1 200 ℃, respectively. Mechanical properties of these fibers were characterized via a monofilament tensile method, with observation of the damaged monofilament by SEM. Also, the effects of annealing on the microstructure and chemical compositions of the fibers were studied. The experimental results indicated that the tensile strength decreased with the increase of annealing temperatures,after annealing-treatment at 1200℃, XD-SiC fibers remained 84% of its original strength, while Nicalon-201 fibers remained only 58% of its original strength. Crystallization and chemical composition of the fibers are the dominating factors for their mechanical performance at high temperatures. The microstructure changes of XD-SiC fibers are mainly composed of the growth of β-SiC, for Nicalon-201 fibers, evaporation of gases is the main change for microstructure.
文摘The tensile strength of CVD SiC fiber was remarkably improved by electrochemical surface treatment. SEM analyses reveal that AC current treatment could form a more compact and complete SiO2 layer than DC current on the surface of the SiC fiber, which was beneficial to the improvement of tensile strength. It was also verified that AC current was more effective for producing high performance SiC fiber with SiO2 surface layer than DC current. The frequency is a sensitive parameter for the process; but the signals of input current had relatively small effect on the tensile strength of SiC fiber. A further discussion for this phenomenon was completed. The proposed operational parameters are 0.3 A, 5 kHz of sine wave and 91 m/h of the receiving rate respectively.
文摘In this paper, the creep resistance of 2D braided SiC/SiC composites was studied under the stress conditions of 120MPa and 140MPa at 1200℃. The creep curve is obtained through the experiment. Through the analysis and calculation of the creep curve, the material has excellent creep resistance in the environment of 1200℃ and 120MPa, and the creep resistance is reduced due to higher stress in the environment of 1200℃ and 140MPa. Through calculation, the average creep rate of the materials under the two stresses is (5±1) × 10-8/s, (1.6±0.6) × 10-7/s respectively, and the creep rate is increased by 3.2 times under 140MPa stress.
基金supported by the National Natural Science Foundation of China(No.51371170)
文摘Raman spectroscopy was used to measure Raman spectra of the inner SiC fibers and surface C-rich layers of SiC fibers, composite precursors and SiCf/Ni-Cr-Al composites. The residual stresses of the inner SiC fibers and surface C-rich layers were calculated, and the effect of the(Al + Al_2O_3) diffusion barrier layer on the interfacial residual stress in the composites was analyzed in combination with the interface microstructure and energy disperse spectroscopy(EDS) elements lining maps. The results show that the existence of(Al + Al_2O_3) diffusion barrier improves the compatibility of the SiCf/Ni-Cr-Al interface,inhibits the adverse interfacial reaction, and relieves the residual stress inside SiC fibers and at the interface of composite material. Heat treatment can reduce the residual stress at the interface. As the heat treatment time increases, the residual stress at the interface decreases.
基金Project(50371069) supported by the National Natural Science Foundation of Chinaproject(2006B20) supported by the Doctoral Innovation Foundation of Northwestern Polytechnical University, China
文摘Three types of SiC fibers with different tensile strength were employed to prepare unidirectional titanium matrix composites. The strengths of the original SiC fibers and extracted fibers from the composites were measured. The results show that the mechanical properties of fibers are greatly damaged by the consolidation processing of the composite. The strength data of the extracted fibers are used to predict the strength of the composites according to two theoretic models. The Globe Load-Sharing(GLS) model overestimates the strength of the composites. If the Local Load-Sharing(LLS) model assumes that failure occurs after the formation of a cluster with three broken fibers, the model can predict the strength of the composites exactly.
文摘Air-curing is usually applied to the polymer-derived SiC fibers and, as a result, oxygen is embedded to the material. An effective relationship between oxygen content of the SiC fibers and mass gain of their precursor fibers was established. Results also showed that oxygen content has a great influence on the mechanical properties and excellent tensile strength is usually obtained at the oxygen content of 12%～13%, similar to the density of SiC fibers. Oxygen content has a positive effect on the ceramic yield, and thus, is good to the density and tensile strength; while, oxygen content is also negative to volume content of SiC phase and crystallization of the SiC fibers, and thus, detrimental to the density and tensile strength. Both of the two effects result in the peak behavior of the tensile strength of SiC fibers.
文摘A new SiC fiber was prepared by the pyrolysis of polycarbosilane(PCS)fiber cured with unsaturated hydrocarbons.The fiber,with oxygen content of 4-6 wt%,offers high tensile strength of 2.5-2.8 GPa.The electrical resistivity of the fiber is only about 0.5Ω·cm,much lower than general SiC fiber obtained from traditional air curing process.Degradation of mechanical property in argon and air at high temperature is retarded by 200-300℃with respect to the Nicalon NL-202 fiber.The low electrical resistivity of the fiber exhibits excellent thermal stability,it almost remains 0.4-0.8Ω·cm after thermal exposure test from the room temperature to 1600℃in argon.The low electrical resistivity mainly attribute to an excess carbon layer which is about 50 nm in the circular outer part.
