Mechanical properties and surface characteristics of SiC fibers irradiated by swift heavy ions

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.

Effect of High-temperature Annealing on Mechanical Performance and Microstructures of Different Oxygen SiC Fibers

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.

Microstructural Changes of T1-6A1-4V Matrix by the Incorporation of Continuous SiC Fibers

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.

A review of third generation SiC fibers and SiC_f/SiC composites

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.

Enhancement of the Mechanical Performance of SiCf/Phenolic Composites after High-temperature Pyrolysis Using ZrC/B_(4)C Particles

The composites were prepared by modifying silicon carbide fiber with particles of zirconium carbide(ZrC)and boron carbide(B_(4)C)and incorporating them into a phenolic resin matrix.The influence of ZrC and B_(4)C on the mechanical performance of SiCf/phenolic composites after high-temperature pyrolysis was studied through flexural performance test.The results show that the composite material has good thermal stability and high-temperature mechanical properties.After static ablation at 1400℃ for 15 minutes,the flexural strength of the composite material reaches 286 MPa,which is still 7.3%higher than at room temperature,indicating that the composite material still has good mechanical properties even after heat treatment at 1400℃.

Microstructure Characterization of Long W Core SiC Fiber

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.

Effect of C/Mo Duplex-coating on Thermal Residual Stresses in SiCf/Ti2AlNb Composites

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.

CVD SiC Fiber Electrochemically Treated by AC Current

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.

Ablative behavior and mechanism of SiC_(f) /SiBCZr composites prepared by PIP process

SiC_(f)/SiBCZr composites were prepared by polymer precursor impregnation and pyrolysis process with near stoichiometric ratio SiC fiber preform as reinforcement phase and SiBCZr multiphase ceramic precursor as impregnating reagent.The results highlighted that the SiC_(f)/SiBCZr composites exhibited excellent ablative properties after ablative tests at 1200℃/3600 s and 1400℃/3600 s,and the strength retention rates of the composites reached 90%and 85%,respectively.This was mainly due to the liquid sealing effect of the ablative products represented by B2O_(3) and SiO_(2)∙B_(2)O_(3),which inhibited the ablative reaction by reducing the diffusion rate of the oxidation medium,and the solid pinning effect of the substances represented by SiO_(2),ZrO_(2),and ZrSiO_(4),which could play high viscosity and high strength characteristics to improve anti-erosion ability.The above-mentioned SiC_(f)/SiBCZr composites with corrosion resistance,oxidation resistance,and ablative resistance provided a solid material foundation and technical support for the development of reusable spacecraft hot-end components.

Analysis of Microstructure of Silicon Carbide Fiber by Raman Spectroscopy

The SiC fiber was prepared by chemical vapour depostion, which consists of tungsten core, SiC layer and carbon coating. The microstructure of the fiber was investigated using Raman spectroscopy, illustrating SiC variation in different region of the fiber. The result shows that the SiC layer can be subdivided into two parts in the morphologies of SiC grains; their sizes increase and their orientations become order with increasing distance from the fiber center. It is demonstrated that the mount of free carbon in the fiber is responsible for the variation of SiC grains in sizes and morphologies. The analysis of Raman spectra shows that the predominant β-SiC has extensive stacking faults within the crystallites and mixes other polytypes and amorphous SiC into the structure in the fiber.

Thermal conductivity and bending strength of SiC composites reinforced by pitch-based carbon fibers

In this work,pitch-based carbon fibers were utilized to reinforce silicon carbide(SiC)composites via reaction melting infiltration(RMI)method by controlling the reaction temperature and resin carbon content.Thermal conductivities and bending strengths of composites obtained under different preparation conditions were characterized by various analytical methods.Results showed the formation of SiC whiskers(SiC_(w))during RMI process according to vapor–solid(VS)mechanism.SiC_(w) played an important role in toughening the C_(pf)/SiC composites due to crack bridging,crack deflection,and SiC_(w) pull-out.Increase in reaction temperature during RMI process led to an initial increase in thermal conductivity along in-plane and thickness directions of composites,followed by a decline.At reaction temperature of 1600℃,thermal conductivities along the in-plane and thickness directions were estimated to be 203.00 and 39.59 W/(m×K),respectively.Under these conditions,bending strength was recorded as 186.15±3.95 MPa.Increase in resin carbon content before RMI process led to the generation of more SiC matrix.Thermal conductivities along in-plane and thickness directions remained stable with desirable values of 175.79 and 38.86 W/(m×K),respectively.By comparison,optimal bending strength improved to 244.62±3.07 MPa.In sum,these findings look promising for future application of pitch-based carbon fibers for reinforcement of SiC ceramic composites.

Online preparation of high-quality BN coatings with atomic diffusion based on carbon-free water-soluble precursor

Efficient and environmentally friendly production of high-quality continuous fiber coatings using current preparation methods is highly challenging due to issues such as scale and batch processing restrictions,low deposition rate,high energy consumption,and utilization of multiple environmentally hazardous steps.To address these challenges,we propose a stable and efficient wet chemical deposition coating method for high-throughput online continuous preparation of boron nitride(BN)coatings on ceramic fibers under an ambient environment.Our process involves surface modification,in-situ wet chemical deposition,and heat treatment,and all seamlessly connecting with the ceramic fiber preparation process through continuous stretching.Hydrophilic groups were introduced via surface modification enhancing wettability of the fiber surface with impregnating solution.An in-situ reaction and atom migration improve uniformity and binding of the coating.As a result,outstanding impregnation and adhesion properties are achieved.A comprehensive analysis to evaluate the impact of the BN coatings was conducted,which demonstrates that the BN-coated fibers exhibit a remarkable 36%increase in tensile strength,a 133%increase in fracture toughness,and enhanced temperature resistance of up to 1600℃.It provides a secure and efficient platform for cost-effective production of functional and high-quality coatings through targeted surface modification and rapid stretching impregnation.

An effective strategy towards construction of CVD SiC fiber-reinforced superalloy matrix composite

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.

Improved mechanical properties of SiC fiber reinforced silica-based ceramic cores fabricated by stereolithography

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.

Preparation of SiC Fiber Reinforced Nickel Matrix Composite

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.

Oxidation behaviors of carbon fiber reinforced multilayer SiC–Si_(3)N_(4) matrix composites

Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion(CTEs)and elastic modulus between carbon fiber and SiC matrix.In order to improve the oxidation resistance,multilayer SiC–Si_(3)N_(4) matrices were fabricated by chemical vapor infiltration(CVI)to alleviate the above two kinds of mismatch and change the local stress distribution.For the oxidation of C/SiC with multilayer matrices,matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC–Si_(3)N_(4) matrix to lengthen the oxygen diffusion channels,thereby improving the oxidation resistance of C/SiC,especially at 800 and 1000℃.The strength retention ratio was increased from 61.9%(C/SiC–SiC/SiC)to 75.7%(C/SiC–Si_(3)N_(4)/SiC/SiC)and 67.8%(C/SiC–SiC/Si_(3)N_(4)/SiC)after oxidation at 800℃for 10 h.

Effects of Cr and Al Contents on the Preparation of SiC Fiber-Reinforced NiCrAl Alloy Matrix Composite

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.