PyC interphase growth mechanism and control models of C/SiC composites

To better understand the pyrocarbon (PyC) interphase growth mechanism, a series of experiments was conducted on the PyC deposited on T-300™ and T-700™ carbon fibers by the chemical vapor infiltration (CVI) method. Nine groups of fabrication parameters were used to analyze the effects of deposition temperature, pressure, and residence time on the PyC interphase growth mechanism. Atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Raman spectroscopy, and nanoindentation tests were performed to characterize the microstructures of carbon fibers and PyC interphase. The PyC interphase growth mechanism was discussed, and the relationships between the fabrication parameters, R (C₂/C₆) value, texture type, and interphase thickness were established through numerical simulations. The hardness and modulus of PyC for T-300™ and T-700™ carbon fibers were measured. The tensile behaviors of C/SiC minicomposites with medium and high textures PyC interphases were analyzed. The C/SiC composite with the medium texture PyC interphase possessed the higher fracture strength and failure strain with a longer fiber pullout length at the fracture surface.     

Effect of pyrocarbon interphase texture and thickness on tensile damage and fracture in T-700™ carbon fiber–reinforced silicon carbide minicomposites

In this paper, T-700™ carbon fiber–reinforced silicon carbide (C/SiC) minicomposites with pyrocarbon (PyC) interphase with different textural microstructure and thickness were fabricated using the chemical vapor infiltration method. The interface properties (i.e., textural microstructure, thickness, hardness, and modulus) were obtained through multiple testing methods (i.e., Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and nanoindentation tests). Relationships between the deposition temperature and residence time with the texture type (i.e., low, medium, and high texture) were established. Uniaxial tensile experiments were conducted for C/SiC minicomposites with different PyC interphases to characterize the composite's internal damage evolution and fracture. Relationships between the composite's tensile nonlinear damage evolution, fracture strength and strain, PyC interphase texture, and thickness were established. The composite's tensile strength and fracture strain were the highest for the C/SiC minicomposite with medium-high texture PyC interphase. For the C/SiC minicomposite with the same texture interphase, the composite's tensile strength and fracture strain were affected by the coating thickness. The higher the thickness of the coating, the lower the composite's tensile strength and fracture strain.     

Fabrication and properties of SiCnw-reinforced SiC composites by reactive melt infiltration with BN and PyC interface

To tailor the fiber–matrix interface of SiC nanowires-reinforced SiC (SiC_nw/SiC) ceramic matrix composites (CMCs) for improved mechanical properties, SiC nanowires were coated with BN and pyrolytic carbon (PyC) compound coatings prepared by the dip-coating process in boric acid and urea solution and the pyrolysis of phenolic resin. SiC_nw/SiC CMC with PyC/BN interfaces were fabricated by reactive melt infiltration (RMI) at 1680°C for 1 h. The influences of phenolic resin content on the microstructure and mechanical properties of the CMC were investigated. The results showed that the flexural strength and fracture toughness reach the maximum values of 294 MPa and 4.74 MPa m^1/2 as the phenolic resin content was 16 and 12 wt%, respectively. The displacement–load curve of the sample exhibited a gradient drop with increasing phenolic resin content up to 12 wt%. The results demonstrated that the PyC/BN compound coatings could play the role of protecting the SiC_nw from degradation as well as improving the more moderate interfacial bonding strengths during the RMI.     

Mechanical properties of SiCf/SiC composites with alternating PyC/BN multilayer interfaces

Alternating pyrolytic carbon/boron nitride (PyC/BN)_n multilayer coatings were applied to the KD–II silicon carbide (SiC) fibres by chemical vapour deposition technique to fabricate continuous SiC fibre-reinforced SiC matrix (SiC_f/SiC) composites with improved flexural strength and fracture toughness. Three-dimensional SiC_f/SiC composites with different interfaces were fabricated by polymer infiltration and pyrolysis process. The microstructure of the coating was characterised by scanning electron microscopy, X–photoelectron spectroscopy and transmission electron microscopy. The interfacial shear strength was determined by the single-fibre push-out test. Single-edge notched beam (SENB) test and three-point bending test were used to evaluate the influence of multilayer interfaces on the mechanical properties of SiC_f/SiC composites. The results indicated that the (PyC/BN)_n multilayer interface led to optimum flexural strength and fracture toughness of 566.0?MPa and 21.5?MPa?m^1/2, respectively, thus the fracture toughness of the composites was significantly improved.     

Fabrication and performance of mini SiC/SiC composites with an electrophoresis-deposited BN fiber/matrix interphase

The feasibility of fabricating a BN matrix/fiber interphase of SiC/SiC composites via electrophoresis deposition (EPD) was investigated based on the simplicity and non-destructiveness of the process and the excellent interfacial modification effects of BN. The BN suspension and SiC fiber surface properties were both adjusted to generate suitable conditions for the EPD process of the BN interphase. Next, the deposition dynamics and mechanism were studied under different deposition voltages and time, and the relationship between the deposition morphology of the BN interphase and mechanical properties of the fabricated mini SiC/SiC composites were also discussed. After oxidation at high temperature (600–1000 ℃), the mechanical properties of the mini SiC/SiC composites were studied to verify the oxidation resistance effect of the EPD-deposited BN interphase, whose oxidation resistance mechanism was briefly analyzed as well.     

Effect of interphase on mechanical properties and microstructures of 3D Cf/SiBCN composites at elevated temperatures

Interphase between the fibers and matrix plays a key role on the properties of fiber reinforced composites. In this work, the effect of interphase on mechanical properties and microstructures of 3D C_f/SiBCN composites at elevated temperatures was investigated. When PyC interphase is used, flexural strength and elastic modulus of the C_f/SiBCN composites decrease seriously at 1600°C (92 ± 15 MPa, 12 ± 2 GPa), compared with the properties at room temperature (371 ± 31 MPa, 31 ± 2 GPa). While, the flexural strength and elastic modulus of C_f/SiBCN composites with PyC/SiC multilayered interphase at 1600°C are as high as 330 ± 7 MPa and 30 ± 2 GPa, respectively, which are 97% and 73% of the values at room temperature (341 ± 20 MPa, 41 ± 2 GPa). To clarify the effect mechanism of the interphase on mechanical properties of the C_f/SiBCN composites at elevated temperature, interfacial bonding strength (IFBS) and microstructures of the composites were investigated in detail. It reveals that the PyC/SiC multilayered interphase can retard the SiBCN matrix degradation at elevated temperature, leading to the high strength retention of the composites at 1600°C.     

Improved tensile strength and toughness of dense C/SiC-SiBC with tailored PyC interphase

In this study, in order to improve the tensile strength and toughness of dense C/SiC-SiBC, the thickness of PyC interphase (e_PyC) was increased from 200 nm to 400 nm. C/SiC (e_PyC≈200 nm) was also fabricated as a benchmark comparison. C/SiC-SiBC (e_PyC≈200 nm) exhibited higher axial thermal residual stress (TRS) than C/SiC (e_PyC≈200 nm). Increased axial TRS resulted in increased interfacial shear strength (τ) through fiber bending, which caused lowered mechanical properties of C/SiC-SiBC (e_PyC≈200 nm). By increasing the thickness of PyC interphase from 200 nm to 400 nm, the axial TRS in C/SiC-SiBC decreased. Accordingly, the radial stress induced by fiber bending decreased, leading to a reduced τ in C/SiC-SiBC (e_PyC≈400 nm). Decreased axial TRS and τ are beneficial to the effective loading of fiber bundles and pull out of fibers. Therefore, C/SiC-SiBC (e_PyC≈400 nm) performed excellent tensile strength (250 ± 11 MPa) and fracture toughness (23.7 ± 0.5 MPa·m^1/2).     

Ablative and mechanical properties of C/C-SiC-ZrC composites modified with PyC/SiC and PyC/BN interface layers

Two kinds of novel modified C/C-SiC-ZrC composites were prepared via precursor infiltration and pyrolysis, as pyrocarbon (PyC)/silicon carbide (SiC) and PyC/boron nitride (BN) dual-layer interphases were separately structured on the fibers by means of chemical vapor infiltration. Data analysis and conclusions are served for investigating the effects of these two interface layers on mechanical and anti-ablative properties. On the mechanical property hand, both PyC/BN and PyC/SiC interphase layers play positive roles, resting with the reduction of fiber damage during the fabrication process. Compared with BN, SiC shows better enhancement as the flexural strength of PyC/BN and PyC/SiC interphase-modified composites are 214.9 and 229.2 MPa, respectively. On the ablative property hand, after oxyacetylene flame ablation for 60 s, the mass and linear ablation rates of the composites modified by PyC/SiC interface were 2.2 mg/s and 9.7 μm/s, which is much lower than that modified by PyC/BN. The inferior ablation properties of PyC/BN-CSZ were attributed to the vaporization of the B₂O₃ gas that destroys the integrity of the oxide film and oxygen erosion on the substrate through the damaged BN interface.     

Enhanced mechanical and dielectric properties of SiCf/SiC composites with silicon oxycarbide interphase

SiC_f/SiC composites with silicon oxycarbide (SiOC) interphase were successfully prepared using silicone resin as interphase precursor for dip-coating process and polycarbosilane as matrix precursor for PIP process assisted with hot mold pressing. The effects of SiOC interphase on mechanical and dielectric properties were investigated. XRD and Raman spectrum results show that SiOC interphase is composed of silicon oxycarbide and free carbon with a relatively low crystalline degree. The surface morphology of SiC fibers with SiOC interphase is smooth and homogeneous observed by SEM. The flexural strength and failure displacement of SiC_f/SiC composites with SiOC interphase vary with the thickness of interphase and the maximum value of flexural strength is 289 MPa with a failure displacement of 0.39 mm when the thickness of SiOC interphase is 0.25 µm. The complex permittivity of the composites increases from 8.8-i5.7 to 9.8-i8.3 with the interphase thicker.     

Crystallographic textures and magnetic properties of electroformed nickel

The magnetic properties of nickel deposits are known to be related to their crystallographic textures. Although there has been significant work investigating the relationship between crystallographic textures and magnetic properties of sputtered ferro-magnetic films, relatively less effort has been spent on studying electroformed nickels. Orientation distribution functions and coercivity of the nickel deposits, electroformed by using a nickel sulphamate bath and pulse-reverse currents, have been determined and their relationship examined. It was found that the [100] fibre texture with different orientation densities was formed at different on-times and off-times, and that at the same deposition thickness the coercivity increased with increase in the orientation density of the [100] fibre texture. This findings are of high significance as they can serve as guidelines for the production of nickel deposits with defined magnetic properties through the control of crystallographic te xture by varying the pulse parameters in pulse-reverse current electroforming.     

Effects of oxidation temperature on microstructure and EMI shielding performance of layered SiC/PyC porous ceramics

Herein, the influence of oxidation temperature on the oxidation behavior, microstructure and electromagnetic shielding performance of layered porous ceramics has been systematically investigated. Layered SiC/PyC porous ceramics were prepared by using low-pressure chemical vapor infiltration (LPCVI) method. The oxidized SiC/PyC layered porous ceramics exhibited a negligible mass reduction of 11.94 mg·cm^?3, which indicates the excellent high-temperature oxidation resistance of porous ceramics. The electromagnetic shielding performance of SiC/PyC porous ceramics did not exhibit any obvious change even after oxidation at high temperature from 900 to 1300 °C for 10 h. The SE_T of the layered SiC/PyC porous ceramics was 24.1, 20.0, 19.5, 19.0, 19.8 dB after oxidation at 25 °C, 900 °C, 1000 °C, 1100 °C and 1300 °C, which corresponds to a decrease of 17.01%, 19.09%, 21.16% and 17.84%, respectively. The high-temperature oxidation has rendered a more significant influence on the reflection efficiency of the layered SiC/PyC porous ceramics.     

Nanoscale crystal imperfection-induced characterization changes of manganite nanolayers with various crystallographic textures

(La,Sr)MnO₃ (LSMO) nanolayers with various crystallographic textures were grown on the sapphire substrate with and without In₂O₃ epitaxial buffering. The LSMO nanolayer with In₂O₃ epitaxial buffering has a (110) preferred orientation. However, the nanolayer without buffering shows a highly (100)-oriented texture. Detailed microstructure analyses show that the LSMO nanolayer with In₂O₃ epitaxial buffering has a high degree of nanoscale disordered regions (such as subgrain boundaries and incoherent heterointerfaces) in the film. These structural inhomogeneities caused a low degree of ferromagnetic ordering in LSMO with In₂O₃ epitaxial buffering, which leads to a lower saturation magnetization value and Curie temperature, and higher coercivity and resistivity.     

Microstructure and mechanical properties of carbon/carbon composites with PyC/SiC/TiC multilayer interphases

Carbon/carbon composites with PyC/SiC/TiC multilayer interphases (CCs-PST) have been successfully prepared by a joint process of chemical vapor deposition and carbothermal reduction. Effect of the Ti(OC₄H₉)₄/C₆H₄(OH)₂ molar ratio on the morphology of TiC particles was investigated and the ratio was optimized as 8:1. When the Ti(OC₄H₉)₄/C₆H₄(OH)₂ molar ratio was 8:1, many homogeneously distributed TiC nanoparticles with the sizes of 100–500 nm on the fibers were observed. The structural evolution of CCs-PST was discussed and the mechanical properties of as-prepared materials were investigated by flexural and interlaminar shear tests. The resulted composites demonstrated a PyC and SiC mixed inner interphase with the thickness of 0.5–1 $\mathrm{\mu }\mathrm{m}$ and a TiC outer interphase with a thickness about 0.5 µm. Flexural strength of 201.45 ± 5.27 MPa and modulus of 21.21 ± 1.58 GPa showed a 41.7% and 7.83% improvement respectively as compared with that of the neat CCs. The interlaminar shear strength of CCs-PST was 66.71 ± 4.87 MPa, which was 51.20% higher than that of the CCs. The improved mechanical properties were attributed to the enhanced interface bond between fibers and matrix induced by the PST.     

Fabrication and characterization of novel zirconia filled glass fiber reinforced polyester hybrid composites

Novel hybrid glass fiber reinforced polyester composites (GFRPCs) filled with 1‐5 wt % microsized zirconia (ZrO₂) particles, were fabricated by hand lay‐up process followed by compression molding and evaluated their physical, mechanical and thermal behaviors. The consumption of styrene in cured GFRPCs was confirmed by Fourier transform infrared spectroscopy. The potential implementation of ZrO₂ particles lessened the void contents marginally and substantially enhanced the mechanical and thermal properties in the resultant hybrid composites. The GFRPCs filled with 4 wt % ZrO₂ illustrated noteworthy improvement in tensile strength (66.672 MPa) and flexural strength (67.890 MPa) while with 5 wt % ZrO₂ showed 63.93% rise in hardness, respectively, as compared to unfilled GFRPCs. Physical nature of polyester matrix for composites and an improved glass transition temperature (T_g) from 103 to 112 °C was perceived by differential scanning calorimetry thermograms. Thermogravimetric analysis revealed that the thermal stability of GFRPCs was remarkably augmented with the addition of ZrO₂. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43615.     

Fabrication of Surlyn ionomer fibers using a novel coextrusion approach and mechanical property characterization

We report the fabrication of poly (ethylene-co-methacrylic acid) sodium-neutralized ionomer (Surlyn 8940) fibers via a forced-assembly coextrusion and layer multiplication process with polystyrene (PS) as the matrix material. The PS separating materials were removed by toluene extraction to yield independent Surlyn fibers. The tensile properties of Surlyn fiber strands were studied under different strain rates. Surlyn fibers were oriented to 300% strain at different temperatures to study the effect of orientation on the tensile properties. The oriented Surlyn fibers were annealed after orientation to further enhance the mechanical properties. Further drawing of these oriented fiber mats to a draw ratio of 4 at 60 °C followed by annealing at 60 °C can afford moduli in excess of 350 MPa and tensile strengths in excess of 70 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48046.     

Characterization of the passive inorganic interphase and polypyrrole coatings formed on steel by the aqueous electrochemical process

Polypyrrole coatings have been successfully formed on steel from aqueous oxalic acid‐pyrrole solutions by electrochemical polymerization. Formation of the coatings was found to be dependent on the pH of the reaction solution and the applied current. In acidic medium, the formation of polypyrrole was characterized by an induction (passivation) period before electropolymerization of pyrrole. At the end of the induction period, a crystalline passive interphase was formed. The morphology and composition of the electrodeposited passive interphase and the resultant polypyrrole coatings were investigated by scanning electron microscopy, reflection‐absorption infrared spectroscopy, and X‐ray photoelectron spectroscopy. Our results reveal that the chemical composition of the passive interphase was similar to that of iron(II) oxalate dihydrate, FeC₂O₄ · 2H₂O, crystals. Size and orientation of the crystalline passive interphase varied with electrochemical process variables. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2075–2086, 1999     

Friction behaviors of carbon/carbon composites with different pyrolytic carbon textures

Friction and wear properties of carbon/carbon (C/C) composites with a smooth laminar (SL), a medium textured rough laminar (RL) and a high textured RL pyrolytic carbon texture were investigated with a home-made laboratory scale dynamometer to simulate airplane normal landing (NL), over landing (OL) and rejected take-off (RTO) conditions. The morphology of worn surfaces at different braking levels was observed with scanning electron microscopy. The results show that C/C composites with RL have nearly constant friction coefficients, stable friction curves and proper wear loss at different braking levels, while friction coefficients of C/C composites with SL pyrolytic carbon decrease intensely and their oxidation losses increase greatly under OL and RTO conditions. Therefore, C/C composites with a high and medium textured RL pyrolytic carbon may satisfy the requirements of aircraft brakes. The good friction and wear properties of C/C composites with RL are due to the properties of RL, which leads to a uniform friction film forming on the friction surface.     

Fabrication of continuous nanofiber yarn using novel multi‐nozzle bubble electrospinning

A novel multi‐nozzle bubble electrospinning apparatus, including spinning unit, metering pump, constant flow pump, metal funnel and yarn winder, was designed for the preparation of continuous twisted polyacrylonitrile nanofiber yarns, and the principle of nanofiber yarn spinning was studied. An innovative spinning unit consisting of nozzle and air chamber was used to improve the production of nanofibers. Double conjugate electrospinning was developed using two pairs of oppositely charged spinning units to neutralize the charges. The effects of applied voltage, air flow rate, overall solution flow rate and funnel rotary speed on the fiber diameter, production rate and mechanical properties of the nanofiber yarns were analyzed. Nanofibers could be aggregated stably and bundled continuously, then twisted into nanofiber yarns uniformly at an applied voltage of 34 kV, air flow rate of 1200 mL min^?1 and overall solution flow rate of 32 mL h^?1. With an increase in the funnel rotary speed, the twist angle of the nanofiber yarns gradually increased when the take‐up speed was constant. The yarn tensile strength and elongation at break showed an increasing trend with increasing twist angle. Nanofiber yarns obtained using this novel method could be produced at a rate from 2.189 to 3.227 g h^?1 with yarn diameters ranging from 200 to 386 µm. Nanofiber yarns with a twist angle of 49.7° showed a tensile strength of 0.592 cN dtex^?1 and an elongation at break of 65.7%. © 2013 Society of Chemical Industry     

A novel process of preparing glass-ceramics with pseudo-bioclastic texture

Water quenching-induced cracked-glass was used as parent glass to prepare glass-ceramics in this work. The cracked-glass panel was first heat-treated through two-step method, i.e. sintering for 1 h at 860 °C and subsequent crystallization for 1.5 h at 1080 °C, and then naturally cooled down to room temperature to be transformed into glass-ceramics. XRD and SEM observations confirm that the cracked-glass can be used as parent glass to deposit β-wollastonite crystals depending on crack crystallization mechanism. The volume densities, porosities and bending strengths of the glass-ceramics are respectively around 2.7 g/cm³, 0.5% and 40 MPa. As compared with glass-ceramics prepared by conventional glass grain sintering process, the new type of glass-ceramics produced by CGC process shows pseudo-bioclastic texture and has less gas pore flaws, and may therefore become an alternative for materials of architectural decoration.