Processing and properties of Nextel™ 720 fiber reinforced alumina-zirconia ceramic matrix composites

The continuous Nextel? 720 fiber-reinforced zirconia/alumina ceramic matrix composites (CMCs) were prepared by slurry infiltration process and precursor infiltration pyrolysis (PIP) process. The introduction of submicron zirconia powders into the aqueous slurry was optimized to offer comprehensively good sintering activity, high thermal resistance and good mechanical properties for the CMCs. Meanwhile, the zirconia and alumina preceramic polymers were used to strengthen the porous ceramic matrix through the PIP process. The final CMC sample achieved a high flexural strength of 200 MPa after one infiltration cycle of alumina preceramic polymer and thermal treatment at 1150 °C for 2 h. The flexural strength retention of the improved CMC sample was 104% and 89% respectively after thermal exposure at 1100 °C and 1200 °C for 24 h.     

All-oxide ceramic matrix composites (OCMC) based on low cost 3M Nextel™ 610 fabrics

Cost reduction without loss of quality is a key factor during the development of engineering materials. This is particularly true for oxide fibers, which can represent up to 70 % of the real cost of all-oxide ceramic matrix composites (OCMC). Therefore, the objective of this work is to produce and evaluate OCMCs based on novel low-cost Nextel? 610 fiber fabrics with deniers of 3000?20,000. Experiments were divided into fiber and composite characterizations. In general, fiber bundles with higher denier show lower apparent strength; although fiber characteristic strength is very similar for bundles with denier below 4500. Composite characterization showed that certain properties, such as tensile strength, are in accordance to the measured fiber characteristic strength. Other properties like interlaminar shear strength and notch sensitivity did not depend on the type of fabric used. In summary, composites with the new fiber fabrics were successfully produced, showing properties similar to commercially available OCMCs.     

On the mechanical,thermophysical and dielectric properties of Nextel™ 440 fiber reinforced nitride matrix (N440/Nitride) composites

The Nextel? 440 fiber reinforced nitride matrix (N440/Nitride) composites were fabricated by precursor infiltration and pyrolysis (PIP) route. The results demonstrated that the original N440 fiber had a phase composition of amorphous SiO₂ and γ-Al₂O₃. Its single filament tensile strength was 3.03 GPa (at room temperature), while it dropped to 72.6% and 35.1% at 1200 °C and 1400 °C, respectively. The phase content of N440/Ntride composites was mainly γ-Al₂O₃ and amorphous BN, as well as mullite phase (formed at > 1100 °C). The composites owned a flexural strength up to 76.0 MPa at room temperature. The stair-stepping decrease in the load-displacement curve and fiber pull-outs in the fracture surface indicated a good fiber/matrix interface and toughness. By heating at 1400 °C, the composites still possessed 67.4% of original bending strength. It was found that the high temperatures caused strong fiber-matrix bonding and severe fiber degradation. The specific heat, CTE and thermal conductivity of the composites were 0.325–0.586 J g^?1 K^?1, (3.2–4.0) × 10^?6 K^?1 and 0.78–3.47 W m^?1 K^?1, respectively. The composites possessed a dielectric constant of 4.25–4.35 and loss tangent of 0.004–0.01 at 8–12 GHz. The good overall performances enabled the N440/Nitride composites advanced high-temperature wave-transparent applications.     

Relationships between the accumulative damage and dielectric properties of woven BN-coated Hi-Nicalon™ SiC fibre-reinforced SiC matrix composites

The accumulative damage behaviour of BN-coated Hi-Nicalon™ SiC fibre-reinforced SiC matrix composite was examined under tensile cyclic loading at room and elevated temperatures. The accumulative damage occurring during the cyclic loading was quantitatively characterised using the damage parameter obtained by the hysteresis loop curves. The damage parameter increased with increasing applied stress beyond the matrix cracking stress, and it subsequently retained a nearly constant value until just before fracture. Moreover, the dielectric constant, dielectric loss and loss tangent of the composite were measured before and after the fracture in the frequency range 1–1000 MHz. The dielectric properties had similar frequency dependency before and after the fracture. However, the dielectric constant, dielectric loss and loss tangent were lower in the post-fractured specimens than in the pristine ones. The reduction of the dielectric properties was associated with the accumulative damage stored in the specimens. In addition, the relationships between the dielectric properties and the damage parameter were described in detail.     

Joining and mechanical testing of oxide/oxide (Nextel ™610/alumina-zirconia) ceramic composites

Efficient joining materials and techniques are of critical importance for the integration of CMCs in high performance structures. Continuous oxide fiber Nextel^? 610/alumina-zirconia composites were successfully joined to themselves by using a novel glass-ceramic based on the SiO₂-CaO-Al₂O₃-MgO-Y₂O₃-ZrO₂ system.Crystallization kinetic of the novel glass-ceramic was studied using Matusita, Sakka and Ozawa equations. Single lap off-set shear tests and four-point bending tests were performed at room temperature and at 850 °C to investigate the mechanical strength of the joints. Thermal ageing was performed at 850 °C for 100 h in air to check the thermal stability of the joined components. The results showed that the joints were oxidation resistant and the joined interfaces were well bonded. Single lap off-set shear tests on joined samples resulted in delamination of the composites. The average flexural strengths of the joined samples were 71 MPa and 81 MPa, at room temperature and at 850 °C, respectively.     

P(VDF–TrFE–CFE)-based percolative composites exhibiting significantly enhanced dielectric properties

All-organic three-component composites were fabricated by embedding conductive polyaniline (PANI) into a dielectrically enhanced matrix of poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene) [P(VDF–TrFE–CFE)] with both chemically grafted and physically blended copper phthalocyanine oligomer (CuPc). Dielectric behavior of the composites with different volume fraction of dispersed PANI phase can be described by percolation theory. One of such composites with the PANI content close to the percolation threshold (f _c = 0.146) has a dielectric constant 516 and a loss factor of 0.51 at 100 Hz, and the breakdown field is 28.0 MV/m. The composite remains very flexible with an elastic modulus close to that of the parent copolymer.     

Thermophysical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Three kinds of carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites (n = 1, 2 and 4) were prepared by means of layer-by-layer deposition of PyC and SiC via chemical vapor infiltration. Thermal expansion behaviors in the temperature range of 800–2500 °C and thermal conductivity from room temperature to 1900 °C of C/(PyC–SiC)_n composites with various microstructures were investigated. The results show that with increasing PyC–SiC sequences number (n), the coefficients of thermal expansion of the composites decrease due to the increase of interfacial delamination, providing room for thermal expansion. The thermal diffusivity and thermal conductivity also decrease with the increase of sequences number, which are attributed to the enhancement of phonon-interface scattering resulted from the increasing number of interfaces. Modified parallel and series models considering the interfacial thermal resistance are proposed to elaborate thermal conductivity of the composites, which is in accordance with the experimental results.     

Effects of storage on thermomechanical properties of poly(ɛ-caprolactone) blends containing poly(vinyl pyrrolidone/iodine)

Abstract

This study reports the effects of: the molecular weight ratio of poly(?-caprolactone) (PCL) in blends containing polymer of high (50 000 g mol^-1 ) and low (4000 g mol^-1 ) molecular weight; the concentration (0, 1, and 5 wt-%) of poly(vinyl pyrrolidone/iodine) (PVP/I); and storage at 30°C and 75% relative humidity; on the thermomechanical properties of films prepared by solvent evaporation from solutions containing both PCL and PVP/I. The tensile properties were found to be statistically dependent on the molecular weight ratio of PCL but not on the concentration of PVP/I. The reductions in tensile strength and elongation at break associated with increasing amounts of low molecular weight PCL were attributed to a reduction in the concentration of chain entanglements. No changes were observed in viscoelastic properties or the glass transition temperature. Following storage there were no changes in the tensile strength, glass transition temperature, or viscoelastic properties of the films; however, significant reductions in elongation at break were observed. It is suggested that this is due to hydrolytic chain scission of amorphous PCL. Inclusion of 5 wt-% PVP/I increased this process in films containing 100 : 0 and 80 : 20 high/low molecular weight PCL (but not 60 : 40), but the extent of this was small. This study highlighted significant aging properties of PCL in a moist atmosphere. Consequently, it is recommended that suitable packaging materials should be employed to control the exposure of PCL films to water during storage.     

Structures and mechanical properties of electrospun cellulose nanofibers/poly(ε-caprolactone) composites

Poly(ε-caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA-NF) and the cellulose nanofibers (C-NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA-NF were prepared by electrospinning and converted into C-NF afterward by deacetylation. It was found that the Young's modulus of the CA-NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C-NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA-NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C-NF/PCL could not reach the theoretical values. It indicates that CA-NF possessed better compatibility with PCL than C-NF, agreeing well with the fracture-surface analyses of the two composites by the scanning electron microscopy.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)??nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150?°C and 20?MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E??) and loss modulus (E??) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)—nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150 °C and 20 MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E’) and loss modulus (E”) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

The processing and properties of (Zr,Hf)B2–SiC nanostructured composites

(Zr, Hf)B₂–SiC nanostructured composites were fabricated by high energy ball milling and reactive spark plasma sintering (RSPS) of HfB₂, ZrSi₂, B₄C and C. Highly dense composites with homogeneously intermixed ultra-fine (Zr, Hf)B₂ and SiC grains (100–300 nm) were obtained after RSPS at 1600 °C for 10 min. The densification was promoted by high energy ball milling and ZrSi₂ additive. The additives were almost completely transformed into ZrB₂ and SiC during densification. The improvement of flexural strength and fracture toughness (641 MPa and 5.36 MPa m^1/2, respectively) was achieved. The relationships between the ultra-fine microstructure and mechanical properties were discussed.     

Improved dielectric properties of poly(vinylidene fluoride)–BaTiO3 composites by solvent-free processing

Composites of poly(vinylidene fluoride) (PVDF) and BaTiO₃ nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent-free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·10⁴ Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents.     

Fullerene (C60)–transitional metal (Ti) composites: Structural and biological properties of the thin films

Thin films of the binary C₆₀/Ti composites (with various phase ratios) were deposited on the Si(001) wafers and microscopic glass coverslips in continuous and micropatterned forms. The composites acquired a nanogranular structure with granules of about 50 nm in size. The RBS inspection confirmed homogeneous distribution of the phases and also the presence of oxygen. The Raman study suggested polymerization of the C₆₀/Ti composites into polymeric structures. The hybrid substrates were tested on biocompatibility—the films were seeded with human osteoblast-like MG 63 cells, and their proliferation was analyzed for 7 days. It has been found that the C₆₀/Ti composites can be counted as good supports for the adhesion of the selected MG 63 cells. The composites exhibited similar biocompatibility as the mix of amorphous carbon and titanium, but different than fullerene (C₆₀) solids.     

Nonlinear optical properties of (1−x) CaFe2O4–xBaTiO3 composites

In this paper, we report nonlinear optical properties of a composite nanostructure with the general formula (1−x) CaFe₂O₄–(x) BaTiO₃ (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) prepared by sol–gel and conventional solid-state reaction methods. Structural properties and chemical compositions of the samples were characterized using XRD and HRTEM. Basic optical constants, band gap energy and linear absorption coefficient were calculated through optical absorbance measurements. The nonlinear optical properties were investigated using the single-beam open aperture Z-scan technique. The obtained nonlinearity fits to Two-photon absorption process and all samples display high nonlinear absorption effect. The incorporation of BaTiO₃ into CaFe₂O₄ systems show a significant improvement in the nonlinear optical properties. These composite that exhibit efficient optical limiting can have potential applications in photonic devices.     

Microstructure,mechanical properties and thermal conductivity of (Ti0.5Nb0.5)C–SiC composites

A series of (Ti_0.5Nb_0.5)C-x wt.% SiC (x = 0, 5, 10, 20) composites were prepared by spark plasma sintering. Dense microstructures with well‐dispersed SiC particles were obtained for all composites. With the increment of SiC content, the Vickers hardness, Young's modulus and fracture toughness increase monotonically. An optimized flexural strength of 706 MPa was achieved in (Ti_0.5Nb_0.5)C-5 wt.%SiC composite. (Ti_0.5Nb_0.5)C-20 wt%SiC composite exhibits the highest fracture toughness of 6.8 MPa m^1/2. The crack deflections and the suppression of grain growth were the main strengthening and toughening mechanisms. Besides, (Ti_0.5Nb_0.5)C-20 wt%SiC composite exhibit the highest thermal conductivity of 45 W/m·K at 800 °C.     

Mechanical properties of poly(ε-caprolactone) composites with electrospun cellulose nanofibers surface modified by 3-aminopropyltriethoxysilane

To enhance the reinforcement effects of regenerated cellulose nanofibers (RC-NF) in poly(ε-caprolactone) (PCL), we synthesized RC-NF-3-aminopropyltriethoxysilane (APS), the surface-modified RC-NF by APS. The RC-NF were fabricated by the saponification of electrospun cellulose–acetate nanofibers. The surface modification by APS was confirmed by the X-ray photoelectron spectroscopy (XPS). To enhance the mechanical property of PCL, the RC-NF and the RC-NF-APS were separately compounded into PCL by compression molding. It was found that, when the fiber concentration of RC-NF-APS was 17 wt %, the Young's modulus at room temperature increased from 698.0 to 744.7 MPa, whereas the storage modulus at 55 °C almost increased from 180 to 220 MPa. The micrographs of the fracture surface of the composites revealed that the surface modification prevented the pull-out of RC-NF from PCL. It was concluded that the mechanical properties of the composites were enhanced due to the improvement of the compatibility between RC-NF and PCL by the surface modification with APS. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48599.     

Bond characteristics,mechanical properties,and high-temperature thermal conductivity of (Hf1−xTax)C composites

Bond characteristics, mechanical properties, and high-temperature thermal conductivity of ultrahigh-temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first-principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high-temperature thermal conductivity.     

Detailed electrical and mechanical retention characteristics of MoSi2–RSiC composites exhibiting three-dimensional (3D) interpenetrated network structure during long-term high-temperature oxidation process

MoSi₂–RSiC composites were prepared via a combination of precursor impregnation pyrolysis and high-temperature melt infiltration, in which re-crystallized silicon carbide (RSiC) was used as matrix. The composition, microstructure, oxidation resistance, electrical and mechanical retention characteristics of the composites during long-term high-temperature oxidation process were studied. SEM images revealed that dense MoSi₂–RSiC composites exhibiting three-dimensional (3D) interpenetrated network structure were obtained. XRD patterns confirmed that the primary compositions of the composites were 6H-SiC and hexagonal MoSi₂, as well as a small amount of Mo_4.8Si₃C_0.6. The weight gain rate of the MoSi₂–RSiC composites was about 50% lower than that of RSiC, indicating that the MoSi₂–RSiC composites possess improved oxidation resistance, which was mainly attributed to the acute decrease in porosity of the composites and the oxidation only occurred on the surface of it. The electrical properties of the MoSi₂–RSiC composites decreased slightly and then reached a flat with the increase in oxidation time, suggesting that the MoSi₂–RSiC composites possessed an excellent electrical retention characteristic. The calculated infactor I of the modified mixture value indicated that the interface combination played a more important role than that of interpenetrated network structure on the electrical retention characteristic of the composites. The composites oxidized for 50 h achieved the maximal flexural strength and elastic modulus, and values were 132.38 MPa (flexural strength) and 335.45 GPa (elastic modulus) for MoSi₂-RSiC-2, respectively, exhibiting 31.30% and 27.7% improvement compared with their initial values. The mechanical properties of MoSi₂–RSiC composites were higher than their original values even after 100 h of oxidation. This phenomenon can be due to the dense 3D interpenetrated network structure of the composites, in which oxidation reaction only occurred on the external surface.     

Mechanical properties and morphology of coal gasification fine slag glass bead-filled acrylonitrile–butadiene–styrene (ABS) composites

Coal gasification fine slag glass beads (CGFSGBs) were processed via an efficient pneumatic separation technique. CGFSGB products (CGFSGB-S1, CGFSGB-S2, and CGFSGB-S3) with different sizes were acquired. The heavy calcium carbonate (CaCO₃) was used as comparative filler. Effects of particle size and geometric shape on mechanical strengths, flow properties, and solid density of filled acrylonitrile–butadiene–styrene (ABS) were investigated. The mechanical strengths of composites decreased with increasing CGFSGB weight fraction, while MFR and solid density increased. The mechanical strengths were found to increase with decreasing CGFSGB size, and spherical surface of the CGFSGB is more beneficial to improve interface adhesion strength than square surface of the CaCO₃. The flow property analysis showed that the ABS/CaCO₃ composites have better fluidity and the advantages in the processing energy consumption. However, the incorporation of CaCO₃ resulted in the higher solid-state density. In summary, CGFSGBs have the potential to replace CaCO₃ in the ABS market. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48601.