Tensile Strength Of SiC Fiber Research Articles

SiC fibers with different diameters exhibiting excellent high-temperature resistance and oxidation resistance

SiC fibers have important application in aerospace and other high-tech equipment due to their excellent mechanical properties and thermal resistance. In this work, SiC fibers with diameters of 9, 14, 60 μm were prepared in order to investigate the influence of different diameters on the precursor-derived SiC fibers. The results showed that the polycrystalline structure and near stoichiometric composition of the SiC-9 and SiC-14 fibers were achieved by the “one-step” approach. However, the sintering for SiC-60 fiber was insufficient due to the largest diameter. Moreover, the tensile strength of SiC fibers decreased from 1.88 GPa to only 0.28 GPa with increment of the fiber diameter. The fibers exhibited excellent high temperature resistance with tensile strength retention reaching over 94% after being kept at 1900 °C in argon for 1 h. Furthermore, the SiC fibers with sintered and densified microstructure showed good oxidation resistance. This work could help to further optimize the structure of the polycrystalline near stoichiometric SiC fibers for higher mechanical and thermal performance.

Role of H2 and Ar as the diluent gas in continuous hot-wire CVD synthesis of SiC fiber

W-core SiC fiber was synthesized with CH3SiCl3 as the precursor by continuous hot-wire CVD approach. Using H2 and Ar as the diluent gas, the temperature profile and the production of atomic hydrogen (H) in high-speed deposition process were studied by computational flow dynamics (CFD) simulation, and the growth kinetics and microstructure of the deposit were systematically investigated. H2 significantly increases the H production, which reduces the formation of amorphous phase and structural defects (e.g. stacking faults and twins) during SiC growth. Ar could establish a steep thermal gradient in reactor, which enhances the deposit’s surface quality. The mean tensile strength of SiC fiber reaches its peak value (3.15 GPa) with H2 at 1200 sccm, and a high Weibull modulus (14.7) is achieved with Ar at 1600 sccm. These findings indicate H2 is crucial to promote the mechanical performance of SiC fiber, while Ar is beneficial to improving its uniformity.

Revealing the formation mechanism of the skin-core structure in nearly stoichiometric polycrystalline SiC fibers

The polymer-derived SiC fibers have broad application prospects in the fields of aerospace, nuclear industry and high-tech weapon. Oxygen plays an essential role in adjusting the composition, structure and tensile strength of SiC fibers. Our studies have found that introducing too much oxygen during air curing process will form the skin-core structure in nearly stoichiometric polycrystalline SiC fibers. In order to reveal the formation mechanism of the skin-core structure, gradient oxygen was introduced into the fibers. The morphologies, phase distributions and defects of the fibers were well characterized. By strictly controlling the introduction of oxygen, the polycrystalline product fiber exhibits intragranular fracture behavior and excellent high-temperature resistance. The retention rate of its tensile strength can reach up to 91% and 61% after exposure at 1800 °C for 1 h and 10 h, respectively. The present results give valuable insights into the structural optimization of the nearly stoichiometric polycrystalline SiC fibers.

Reduced Pressure Curing on Polycarbosilane Precursor for Synthesis of Silicon Carbide Fiber

Low pressure curing method with iodine vapor was used on low softening temperature polycarbosilane (PCS) precursor for fabrication of continuous SiC fiber at relatively low temperature. The low curing temperature can provide with a wide range of softening temperature PCS precursors, especially with low softening PCSs, which have a good spinnability, but many difficulties with conventional oxidation curing method. The low pressure curing method having the presence of iodine vapor have shown the more positive effect on pyrolysis with early stage crystallization of β-SiC at 1300 °C. Crystal size of β-SiC, cured at 0.008 kPa is around 2–3 nm larger than cured at 101 kPa. In addition, the higher tensile strength of SiC fiber at elevated temperature can be obtained at 0.008 kPa with a value of 2.1 GPa, compare to 1.3 GPa at 101 kPa of curing pressure condition.

Mechanical and microwave dielectric properties of SiCf/SiC composites with BN interphase prepared by dip-coating process

Abstract The BN interphase of SiC fiber-reinforced SiC matrix (SiCf/SiC) composites was fabricated by dip-coating process with boric acid and urea as precursor. The results show that the tensile strength of SiC fiber decreases about 30% after BN coating treatment, but the BN coating has little influence on the electrical resistivity of SiC fiber. Compared with the as-received SiCf/SiC composites, the SiCf/SiC composites with BN interphase exhibit a toughened fracture behavior, and the flexural strength is about 2 times that of the as-received SiCf/SiC composites. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in weakening interfacial bonding, which can improve the mechanical properties of SiCf/SiC composites remarkably. Owing to the close dielectric properties between SiC and BN, the complex permittivity of SiCf/SiC composites with and without the BN interphase is similar.

Hot Corrosion, Oxidation and Their Effects on the Tensile Strength of SiC Fiber in Alkaline Melts

An experimental study on the behavior of hot corrosion and oxidation of SiC fiber (Hi-NicalonTM) coated with the film of varied alkaline melts was investigated at 1000°C. The hot corrosion and oxidation of SiC fiber were characterized by specific mass loss. The tensile properties on the fibers before and after hot corrosion were evaluated by room temperature single filament test technique. The specific mass loss and strength retention after hot corrosion indicated that the corrosion effect of Hi-NicalonTM fiber in sodium carbonate was more severe than in sodium sulfate. The corrosion effects of Na2SO4 could be enhanced by addition of small amount of Na2CO3/NaNO3. Scanning electron microscopy (SEM) and X-ray diffractometer (XRD) revealed that the degradation of SiC fiber in corrosive and oxidative environment was mainly related to the interaction between the alkaline melts and silica scale. Furthermore, the excess carbon in Hi-NicalonTM fiber must enhance the hot corrosion and oxidation leading to the degradation in microstructure and mechanical properties.

Microstructure and role of outermost coating for tensile strength of SiC fiber

The detailed microstructure of the SiC fiber surface and the outermost coating of SiC(SCS-6) fiber are observed using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The tensile strengths of the SiC fibers: uncoated fiber (SCS-0), coated fiber (SCS-6) and extracted fiber from fatigue-loaded SiC(SCS-6) fiber-reinforced Ti-15-3 composite are determined. Fractographic analysis is done on these fibers and the mirror radius is compared with the tensile strength. Thickness of the outermost coating is ≈3.6 μm and it consists of three different layers (i.e. sublayers I, II and III). Basically, these sublayers consist of a carbon matrix in which β-SiC crystallites are dispersed. The fracture toughness of the SiC fiber is ≈3.3 MPa m 1/2. The outermost coating increases the fiber strength twofold because it reduces stress concentration at the surface of the SiC fiber. The tensile strength of the extracted fiber (SCS-6) from fatigue-loaded specimens shows a reduced strength which is attributed to the debonding of the outermost coating while the composite is loaded.

Tensile Strength of SiC Fibers

An experimental investigation has been conducted on the effects of gauge length on the tensile strength of SiC fibers. The results show that the overall strength distribution cannot be described solely in terms of the two‐parameter Weibull function. The overall distribution is found to be consistent with two concurrent flaw populations, one of them being characteristic of the pristine fibers, and the other characteristic of the additional flaws introduced into the fiber during processing of the composite.

Influence of interfacial reaction on tensile strength of SiC fiber embedded in a γ-titanium-aluminide alloy

The influences of interfacial reaction on tensile strength of continuous SiC fiber (SCS-6, Textron Specialty Materials) embedded in the Ti-48 at% Al matrix consisting of γ-TiAl and α 2-Ti 3Al compounds were studied. Due to the heat-treatment at 1423 K for various times, four reaction layers were formed; (A) degenerated layer in the periphery of the fiber in which pitts were observed for prolonged heat-treating time, and (B) TiC, (C) Ti 2AlC and (D) Ti 5Si 3 layers in the matrix side. The interfacial debonding between layer (B) and the originally coated C-rich layer observed in the fracture surface of composite samples suggests that the premature fracture of the layers (B)-(D) is not a main reason for the reaction-induced reduction in fiber strength in composites. The tensile strength of the fibers extracted from the composite samples, in which only the layer (A) was contained (the other reaction layers (B)-(D) were removed during extraction), was reduced with increasing heat-treatment time. The reduction could be attributed mainly to the premature fracture of the layer (A) and the pits on its surface.

炭化ケイ素繊維強化エポキシ樹脂の沸騰水中吸水劣化

SiC fiber and glass fiber reinforced epoxy resins (SiCFRP and GFRP), which were fabricated by using matching male and female metal molds, were immersed in boiling water for the periods from 5 to 500 hours. The amount of water absorption of SiCFRP was less than that of GFRP, and those of SiCFRP and GFRP immersed for 100 hours were 38.5mg/cm3 and 76.6mg/cm3, respectively. The amount of water absorption at the time when the width of SiCFRP specimen began to increase was 9.5mg/cm3 against 44mg/cm3 of that of GFRP. ILSS retention of SiCFRP immersed decreased with increasing immersion time, while the diameter, weight and tensile strength of SiC fiber were not affected at all by immersion in boiling water up to 500 hours. The ILSS retension of 74% for SiCFRP immersed for 100 hours was almost the same as that of 76% for GFRP. The reason of such low durability of SiCFRP to hot water was interpretated as the bond between the fiber and resin was weak to water because the surface of SiC fiber was not treated.

Mechanical properties of neutron irradiated SiC fibers

SiC fibers were irradiated at neutron fluences of 8 × 10 23 and 2 × 10 24 n/m 2 in JMTR ( E >1 MeV). The tensile strength of SiC fibers measured at gauge length of 5 mm essentially unchanged after the neutron irradiation, but the strength at a length of 25 mm and 50 mm increased by 40% and 25% after the irradiation, respectively. The tensile strength variations of the irradiated SiC fibers with respect to gauge length were examined in terms of Weibull statistics. The Weibull modulus of the tensile strength in the SiC fibers increased slightly by the neutron irradiation. SiC fibers and SiC fiber reinforced aluminum preform wires (SiC/Al) were irradiated in JOYO ( E > 0.1 MeV) at neutron fluences of 1 × 10 24 , and 1 × 10 24 and 1 × 10 25 n/m 2 , respectively. The mechanical properties of the irradiated SiC fibers and the SiC fibers extracted from the irradiated SiC/Al preform wires were essentially unchanged in comparison with the unirradiated SiC fibers.