SiC Interphase Research Articles

Microstructure, interfacial and mechanical properties of SiC interphase modified C/C-SiC composites prepared by reactive melt infiltration

Interfacial modification can effectively regulate the interfacial properties of ceramic matrix composites. This paper reports on the effect of SiC interphase thickness on the microstructure, interfacial and mechanical properties of C/C-SiC composites. As the SiC interphase thickness increased to 2 μm, the flexural strength and modulus of the C/C-SiC composites increased up to 252 MPa and 40 GPa, an increase of 36 % and 40 %, respectively. Because the SiC interphase protected the carbon fibers from the corrosion of liquid silicon, thereby increasing the effective fiber volume fraction. Furthermore, the increased interfacial shear strength (IFSS) measured by the fiber push-in test improved the load transfer efficiency. Raman spectrum and transmission electron microscopy indicated that the damage process of the interface with high IFSS after the fiber push-in test showed fiber/pyrolytic carbon interface debonding, release of thermal residual stress, and larger upward rebound protrusion of carbon fibers without interface crushing.

Microstructure and mechanical properties of SiCf/SiC–AlN composites prepared by low temperature reactive melt infiltration

In this work, SiCf/SiC–AlN composites were fabricated by low temperature reactive melt infiltration of Si–Al alloy into porous SiCf/C–Si3N4 preforms prepared through slurry brushing. The effect of the preforms pore structure on the melt infiltration was studied, and the erosion behaviors of Si–Al alloy melt on the fibers and the interphases were investigated. The results indicate that the preforms with smaller pore size can hinder the alloy melt infiltration, making it difficult for the infiltration process to proceed adequately. In contrast, when the preforms with larger pore size are utilized, the alloy melt can completely infiltrate into the preforms and form dense SiC–AlN matrix in the intra-fiber bundle by in-situ reaction. Moreover, the bending strength of the composites derived from larger pore size preforms could reach 160.2 MPa, which is about 1.5 times higher than that of the composites derived from smaller pore size preforms. In addition, the damage of the SiC interphase caused by the preforms preparation aggravates the erosion of the internal BN interphase and SiC fibers by Al melt. The eroded interphases and fibers could adversely affect the mechanical properties of both composites. This study lays the foundation for the preparation of the composites with excellent properties.

Effect of CVI SiC interphase on tensile properties of SiC fibers with different surfaces

The microstructure, and tensile properties of as-received SiC fiber and SiC coated fiber with different surfaces were investigated. The surface microstructure and composition of the fibers were analyzed through the AFM, SEM, Raman, AES, and TEM analysis. The SiC fibers were or not desized firstly, and then BN interphase or SiC interphase was deposited by CVI process. The tensile properties of the fibers before and after the deposition of the SiC interphase were evaluated, and the influence of the surface composition of SiC fibers on its tensile properties was studied. The results showed that the fiber surface is rich in free carbon and oxygen. The fibers without interphase showed the best tensile properties than those with coated fibers. After depositing SiC interphase, the tensile strength of SiC monofilament without sizing agent and BN interphase reduced mostly.

Effect of SiC interphase on the mechanical, high-temperature dielectric and high-temperature microwave absorption properties of the SiCf/SiC/Mu composites

In this study, SiC interphase was prepared via a precursor infiltration-pyrolysis process, and effects of dipping concentrations on the mechanical, high-temperature dielectric and microwave absorption properties of the SiCf/SiC/Mu composites had been investigated. Results indicated that different dipping concentrations influenced ultimate interfacial morphology. The SiC interphase prepared with 5 wt% PCS/xylene solution was smooth and homogeneous, and no bridging between the fiber monofilament could be observed. At the same time, SiC interphase prepared with 5 wt% PCS/xylene solution had significantly improved mechanical properties of the composite. In particular, the flexural strength of the composite prepared with 5 wt% PCS/xylene solution reached 281 MPa. Both ε′ and ε′′ of the SiCf/SiC/Mu composites were enhanced after preparing SiC interphase at room temperature. The SiCf/SiC/Mu composite prepared with 5 wt% PCS/xylene solution showed the maximum dielectric loss value of 0.38 at 10 GHz. Under the dual action of polarization mechanism and conductance loss, both ε′ and ε′′ of the SiCf/SiC/Mu composites enhanced as the temperature increased. At 700 °C, the corresponding bandwidth (RL ≤ −5 dB) of SiCf/SiC/Mu composites prepared with 5 wt% PCS/xylene solution can reach 3.3 GHz at 2.6 mm. The SiCf/SiC/Mu composite with SiC interphase prepared with 5 wt% PCS/xylene solution is expected to be an excellent structural-functional material.

Construction of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with good mechanical and anti-ablation properties

Four kinds of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with or without a SiC interphase deposited by isothermal chemical vapor infiltration (ICVI), were designed and fabricated by a joint process of electromagnetic coupling chemical vapor infiltration (ECVI) and precursor infiltration and pyrolysis (PIP). The fabricated composites are macroscopically nonhomogeneous materials with low density, high strength and low ablation rate. The interphase and matrix constituents had remarkable effects on the mechanical and ablation properties of these composites. The C/C-SiC composites with an ICVI-SiC interphase exhibited the highest flexural strength of 306.5 MPa. While the C/C-SiC-ZrC composites with the interphase showed the best anti-ablation performance with low linear and mass ablation rates of 0.37 μm/s and 0.04 mg/cm2·s, respectively, after the ablation for 500 s under an oxyacetylene flame test at around 2000 °C.

Effect of C/SiC interphase on interfacial and mechanical properties of SiC fiber reinforced mullite matrix composites

Continuous SiC fiber reinforced mullite (SiCf/Mu) matrix composite was fabricated via sol–gel process. The capability of fiber coatings to weaken the interfacial interaction, thus to enhance the fracture toughness of the SiCf/Mu composite was explored. The results show that the SiC interphase fabricated by chemical vapor deposition (CVD) process was columnar-grain structured. A thin carbon layer was also produced during the CVD process, forming C/SiC interphase. The interfacial shear strength of the SiCf/Mu composite was significantly reduced from ≈537 to ≈115 MPa after the introduction of C/SiC interphase, as quantified by in situ fiber push-in tests. Accordingly, the macro fracture toughness of the composite was remarkably enhanced from ≈0.9 to ≈10.5 MPa m1/2. The work highlights the efficiency of using C/SiC interphase to weaken the interfacial bonding, thus greatly toughen the SiCf/Mu composite.

Impedance Spectroscopy Study on the Two-phase to Three-phase Transformation in Polymer Derived SiC Pyrolyzed at High Temperature

The electrical behavior and evolution of free carbon phase and ceramic phase in pristine polymer derived (PDC) SiC matrix with high pyrolysis temperature were studied by complex impedance spectroscopy. The results from low pyrolysis temperature (1300-1500°C) showed that the contact resistance at the free carbon and amorphous PDC SiC interphase decreases with increasing pyrolysis temperature. At this temperature range, the dielectric response of the system is not sensitive to the increased ordering of non-ferromagnetic carbon clusters. At higher pyrolysis temperature (1600-1800°C), transformation of free carbon from nanocrystalline carbon to turbostratic phase occurs. This phenomenon leads to the introduction of inductance in the equivalent circuit. The percolative network of turbostratic carbon acts as a conductive helical winding in the PDC system. The study demonstrated that when an alternate current of certain frequency made to flow through the PDC system, it behaves as an inductor. Also, carbon cluster- turbostratic carbon transition observed with microstructural investigation is correlated with the equivalent circuit model.

The Effect of PyC/SiC Compound Interphase on the Properties of PIP SiC/SiC Composite

In order to improve the properties of SiC/SiC composite, chemical vapor infiltration (CVI) process was applied for fabricating the PyC/SiC compound interphase. Precursor infiltration and pyrolysis (PIP) process was used to fabricate SiC matrix. Then an investigation was carried out for the effect of PyC/SiC compound interphase thicknesses on the properties of the composites. According to the results, it was found that the mechanical properties of composites with the PyC/SiC compound interphase are much higher than those of composite with only PyC interphase. The flexural strength, flexural modulus, fracture toughness and interlaminar shear strength of the composites increase gradually when the thickness of CVI SiC interphase is lesser than 2 μm. Further increase of the thickness of CVI SiC interphase to 4μm leads to a continuous increase on the modulus of the composites, while a decrease trend occurs on the flexural strength, fracture toughness and interlaminar shear strength of the composites because of the different coefficients of thermal expansion of the CVI SiC interphase and the PIP SiC matrix. SiC/(PyC/SiCx)/SiC composites showed the better properties of oxidation resistance than those of SiC/PyC/SiC composite. It was due to the survived PyC interphase protected by CVI SiC interphase when the oxygen diffuses into the compound PyC/SiCx intherphase.

Predictions of thermal conductivity and degradation of irradiated SiC/SiC composites by materials-genome-based multiscale modeling

A new materials-genome-based multiscale modeling method is proposed to predict the thermal conductivity of SiC/SiC composites subjected to neutron irradiation. The modeling method bridges different scales from the atomic scale to the macro scale of a 2D SiC/SiC composite. The irradiation-induced point defects in the interphase of SiC/SiC composites are first studied using molecular dynamics simulations to compute the degradation of thermal conductivity as a function of irradiation dose and temperature. The thermal conductivities of SiC fibers, matrices and interphase are then used as input for the new materials genome model to compute the thermal conductivities of 2D SiC/SiC composites subject to neutron irradiation. The predicted thermal conductivities for both unirradiated and irradiated SiC/SiC composites are found to decrease with an increase of temperature while the irradiation effect on interphase needs to be considered for irradiated SiC/SiC composites.

Effects of SiC interphase on the mechanical and ablation properties of C/C-ZrC-ZrB2-SiC composites prepared by precursor infiltration and pyrolysis

Carbon/Carbon (C/C) composites modified with ZrC-ZrB2-SiC particles were prepared by precursor infiltration and pyrolysis (PIP) process. Effects of SiC interphase on the mechanical and ablation properties of C/C-ZrC-ZrB2-SiC composites were investigated. The SiC interphase was deposited through low pressure chemical vapor infiltration (LPCVI). It was found that as the SiC interphase was introduced into the modified C/C composites, the flexural strength increased by 24% and the failure mode showed brittle fracture. The mechanisms for the strengthening of the modified C/C composites with SiC interphase were identified as (I) the deposition of SiC interphase in short-cut webs that strengthened the bonding between fibers and matrix promoting to stress transfer, and (II) the production of weak bonding between fiber bundles and matrix in non-woven webs improved the utilization of carbon fiber strength. SiC interphase increased adhesion between the ablation products and matrix, it could enhance the ablation resistance of the modified C/C composites in short term under the action of the evaporation. However, the long-time ablation resistance was reduced since the ceramic particles could not be incorporated into the composites during preparation due to the existence of SiC interphase.

Effect of interface type on the static and dynamic mechanical properties of 3D braided SiCf/SiC composites

The static and dynamic mechanical properties of three dimensional (3D) braided SiCf/SiC composites with pycrocarbon (PyC) and SiC and without an interphase layer prepared by polymer infiltration and pyrolysis (PIP), were investigated using static and dynamic bending tests as well as microstructural characterization. Test results indicated that the interfacial shear stress, flexural strength, elastic modulus, and storage modulus of 3D braided SiCf/SiC composites with an interphase layer were superior to those the composites without an interlayer; the former also showed a lower internal friction than the latter. Results from Weibull statistical analysis also indicated that the scale parameter σ0 (337.1MPa and 630.6MPa, respectively) and Weibull modulus m (16.85 and 19.91, respectively) of 3D braided SiCf/SiC composites with SiC and PyC interphase were higher than those of composites without an interphase (103.2MPa, 14.02). The composite with the PyC interphase presented the highest flexural strength and the most ductile fractures because it featured relatively ideal interfacial bonding and a layered interphase structure, leading to effective energy-dissipation mechanisms, such as fiber pull-out. The composite with the SiC interphase exhibited highest elastic and dynamic moduli because of strong interfacial bonding and a non-layered rough interphase structure, which enhanced its ability to resist strain. The ideal interface improves load transfer and did not contribute to damping. The occurrence of interfacial damping in the 3D braided SiCf/SiC caused the internal friction to become more sensitive to temperature, frequency and amplitude. The static and dynamic mechanical properties, including internal friction and storage modulus, as well as failure behavior of the 3D braided composites were remarkably affected by the interface type.

Enhanced mechanical and microwave-absorption properties of SiCf/AlPO4 composite with PIP–SiC interphase and the MWCNTs filler

A single-layer radar-absorbing structure in the X-band (8.2GHz to 12.4GHz) was designed and fabricated by blending multi-walled carbon nanotubes (MWCNTs) with the binder matrix of SiC fiber/aluminum phosphate matrix (SiCf/AlPO4) composite. The SiC interphase was successfully prepared on SiC fibers by a precursor infiltration and pyrolysis (PIP) method. The morphology of as-received interphase was observed by SEM, and its structure was characterized by XRD and Raman spectrum. The effects of PIP–SiC interphase on the mechanical and dielectric properties of the composite were investigated. The influence of MWCNTs content on the dielectric and microwave-absorption properties of coated SiCf/AlPO4 composite was discussed. When the content of MWCNTs was between 1.5wt% and 3.5wt% and the composite thickness is in the range of 2.5–3.5mm, the SiCf/AlPO4 composite achieved excellent absorbing wave property in X-band.

Dielectric properties of Cf–Si3N4 sandwich composites prepared by gelcasting

Cf–Si3N4 sandwich composites were prepared by gelcasting using α-Si3N4 powder, SiC-coated carbon fibers and sintering additives as starting materials. The microstructure and composition, dielectric properties of Cf–Si3N4 sandwich composites were investigated. SEM and EDS analysis results reveal that the SiC interphase could effectively overcome incompatibility between carbon fiber and silicon nitride matrix under the condition of pressure-less sintering at 1700°C. The investigation of microwave absorbing property reveals that, compared with the Si3N4 ceramics, both the real (ε׳) and imaginary (ε׳׳) permittivity of Cf–Si3N4 sandwich composites show strong frequency dispersion characteristics at X-band. Microwave absorption ability of the Cf–Si3N4 sandwich composites are significantly enhanced compared with pure Si3N4 ceramic, and the reflection loss gradually decreases from −3.5dB to −14.4dB with the increase of frequency, while the pure Si3N4 ceramic keeps at −0.1dB. Particularly, the relationship between permittivity of Cf–Si3N4 sandwich composites and frequency at X-band has been established through an equivalent RC circuit model. Results showed that both ε׳ and ωε׳׳ are inversely proportional to the frequency square ω2, and the predicted results agree quite well with the measured data.

Electromagnetic interference shielding effectiveness of SiCf/SiC composites with PIP–SiC interphase after thermal oxidation in air

SiCf/SiC composites with PIP–SiC interphase were prepared as electromagnetic interference (EMI) shielding materials by chemical vapor infiltration method. Effects of thermal oxidation on electrical and EMI shielding properties of the composites in X band were investigated. The as-received composites show high electrical conductivity of 0.12 S/cm and SET value of 29 dB, which is ascribed to the free carbon in the composites. The electrical conductivities and weight retentions of the composites decrease with oxidation temperatures or time increase. Likewise, the shielding properties deteriorate to some degree but the SET value exhibits more than 17 dB after oxidation at 1000 °C for 2 h and 15 dB at 900 °C for 6 h, respectively. The deterioration of electrical and EMI shielding properties during oxidation process is ascribed to the consumption of free carbon. The high SEA value and low SER value imply that absorption is the dominant EMI shielding mechanism. The SiC interphase can protect the fibers and keep EMI shielding properties of the composites at a high level.

Creep behavior of a zirconium diboride–silicon carbide composite

Abstract Flexural creep studies of ZrB 2 –20 vol% SiC ultra-high temperature ceramic were conducted over the range of 1400–1820 °C in an argon shielded testing apparatus. A two decade increase in creep rate, between 1500 and 1600 °C, suggests a clear transition between two distinct creep mechanisms. Low temperature deformation (1400–1500 °C) is dominated by ZrB 2 grain or ZrB 2 –SiC interphase boundary and ZrB 2 lattice diffusion having an activation energy of 364 ± 93 kJ/mol and a stress exponent of unity. At high temperatures (>1600 °C) the rate-controlling processes include ZrB 2 –ZrB 2 and/or ZrB 2 –SiC boundary sliding with an activation energy of 639 ± 1 kJ/mol and stress exponents of 1.7 n n = 2.2. Microstructure observations show cavitation may partially accommodate grain boundary sliding, but of most significance, we find evidence of approximately 5% contribution to the accumulated creep strain.

Properties of Cf/SiC composites modified by a boron- containing phase

Cf/SiC composites added with a self-healing boron-containing phase (Cf/SiC-B) was fabricated by slurry infiltration. The slurry was mixed with a boron-containing precursor and boron powders. By vacuum impregnation process, it can be well permeated into the fiber preforms and filled within the fiber intra-bundle zones. After heat treatment, the slurry was converted into B4C and SiC phases. It was found that the addition of the boron-containing phase led to a significant increase in the SiC matrix crystallinity. Compared with pyrolytic carbon (PyC) interphase, non-catastrophic failure was observed for the Cf/SiC-B composites with SiC interphase. Experimental results show that the oxidation resistance of Cf/SiC-B composites was improved, and that boron oxides formed during Cf/SiC-B composites’ exposure in air at 700 °C.

The effects of CVD SiC interphase on mechanical properties of KD-1 SiC fiber reinforced aluminum phosphate composites

► The SiC fiber reinforced aluminum phosphate composites were fabricated. ► The SiC interphase can protect the fibers from damage during the process. ► The SiC interphase thickness was optimized as 1.5 μm. ► The anti-oxidation of composites was evaluated. The KD-1 SiC fiber reinforced aluminum phosphate (SiC/Al(PO 3 ) 3 ) composites were fabricated by the method of vacuum infiltration and heat treatment using Al(H 2 PO 4 ) 3 as precursor. The major phases of matrix are cubic Al(PO 3 ) 3 and monoclinic Al 2 P 6 O 18 . The KD-1 SiC fibers are degraded by the water vapor released from Al(H 2 PO 4 ) 3 . In order to protect the KD-1 SiC fibers, the CVD SiC are coated on fibers before infiltration of aluminum phosphate. It was found that the flexural strength of composites enhances as increasing of CVD SiC thickness, but the fracture behavior exhibits brittle rupture when the interphase is too thick. The thickness of CVD SiC interphase is optimized as 1.5 μm from the mechanical properties point of view. In addition, the effects of heat treatment in air on mechanical properties of SiC/Al(PO 3 ) 3 composites were researched. The retentions of flexural strength of SiC/Al(PO 3 ) 3 composites with 1.5 μm CVD SiC interphase after heat treatment in air at 800, 900, 1000 °C for 6 h are 90.3%, 70.9% and 67.20%, respectively.

Effect of PyC Content in C/C Greenbody on Structure and Properties of 3D-C/SiC Composite Fabricated by Gas Silicon Infiltration

In order to fabricate high perform carbon fiber reinforced silicon carbide matrix composite (C/SiC). SiC interphase of three dimensional(3D) braided carbon fiber performs was prepared by polymer infiltration pyrolysis(PIP) using polycarbosilane(PCS) as precursor. Then, C/SiC composites were fabricated by gas silicon infiltration(GSI) at 1400～1700°C to C/C greenbody, which was prepared by PIP based on precursor of phenolic resin from one to four cycles. The influence of pyrocarbon(PyC) content in C/C greenbody on the composition, microstructure and mechanical properties of C/SiC composites was investigated via X-ray diffraction(XRD), scanning electron microscope (SEM), physical and chemical methods. The results indicate that there were β-SiC, residual Si ,C and closed pores in C/SiC, and the different pyrocarbon(PyC) content influenced C/SiC mechanical properties via the variable content of β-SiC, residual Si, C and closed pores. The C/SiC composites with 2 cycles of PIP-C, which had fitting relative content of β-SiC, residual Si and C, possessed the best mechanical properties. The flexure strength and flexure modulus were 187.3MPa and 66.5GPa. The β-SiC generated from PCS wrapped the carbon fiber bundles, protecting them from reacting with gaseous silicon. The phenomenon of ‘fibers pull-out’ was observed in all four groups of C/SiC composites, which manifested the mechanism of toughness fracture.

Hi‐NicalonTM‐SSiC Fiber Oxidation and Scale Crystallization Kinetics

The oxidation and scale crystallization kinetics of Hi‐NicalonTM‐S SiC fibers were measured after oxidation in dry air between 700° and 1400°C. Scale thickness, composition, and crystallization were characterized by TEM with EDS, supplemented by SEM and optical microscopy. TEM was used to distinguish oxidation kinetics of amorphous and crystalline scales. Oxidation initially produces an amorphous silica scale that incorporates some carbon. Growth kinetics of the amorphous scale was analyzed using the flat‐plate Deal‐Grove model. The activation energy for parabolic oxidation was 248 kJ/mol. The scales crystallized to tridymite and cristobalite, starting at 1000°C in under 100 h and 1300°C in under 1 h. Crystallization kinetics had activation energy of 514 kJ/mol with a time growth exponent of 1.5. Crystalline silica nucleated at the scale surface, with more rapid growth parallel to the surface. Crystalline scales cracked from thermal residual stress and phase transformations during cool‐down, and during oxidation from tensile hoop growth stress. High growth shear stress was inferred to cause intense dislocation plasticity near the crystalline SiO2–SiC interphase. Crystalline scales were thinner than amorphous scales, except where growth cracks allowed much more rapid oxidation.

Effect of SiC coating and heat treatment on damping behavior of C/SiC composites

Three groups of 2D and 3D C/SiC composites were fabricated by chemical vapor infiltration (CVI) process: the first group was as received, the second group was treated at 1500 °C in vacuum atmosphere for 2 h, and the third group was deposited with a chemical-vapor-deposited (CVD) SiC coating. Damping properties of these composites were measured by dynamical mechanical analyzer (DMA) at different frequencies from room temperature to 400 °C in air atmosphere. The results show that SiC coating and heat treatment decrease damping capacity of C/SiC composites and the damping peak disappears or decreases in the testing temperature range. The effect of CVD SiC coating on damping behavior of 2D and 3D C/SiC composites is mainly related to the change of porosity and is independent of fiber preform architecture. However, the effect of heat treatment on damping behavior of 2D and 3D C/SiC composites is mainly attributed to the change in the SiC matrix and interphase bonding, and it is dependent on fiber preform architecture. Both of CVD SiC coating and heat treatment studied in this paper have no influence on relationship between damping behavior of C/SiC composites and frequency.