Effects of steam environment on creep behavior of Nextel™720/alumina–mullite ceramic composite at elevated temperature

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1000 and 1100 °C in laboratory air and in steam. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel?720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. The presence of steam accelerated creep rates and dramatically reduced creep lifetimes. The degrading effects of steam become more pronounced with increasing temperature. At 1000 °C, creep run-out (set to 100 h) was achieved in all tests. At 1100 °C, creep run-out was achieved in all tests in air and only in the 87.5 MPa test in steam. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Tension-Compression Fatigue of a Nextel™720/alumina Composite at 1200 °C in Air and in Steam

Tension-compression fatigue behavior of an oxide-oxide ceramic-matrix composite was investigated at 1200 °C in air and in steam. The composite is comprised of an alumina matrix reinforced with Nextel?720 alumina-mullite fibers woven in an eight harness satin weave (8HSW). The composite has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension-compression fatigue behavior was studied for cyclical stresses ranging from 60 to 120 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was ?1.0. Fatigue run-out was defined as 10⁵ cycles and was achieved at 80 MPa in air and at 70 MPa in steam. Steam reduced cyclic lives by an order of magnitude. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Specimens subjected to prior cyclic loading in air retained 100 % of their tensile strength. The steam environment severely degraded tensile properties. Tension-compression cyclic loading was considerably more damaging than tension-tension cyclic loading. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Nextel™ 610 alumina fibre reinforced aluminium: influence of matrix and process on flow stress

Continuous alumina fibre reinforced aluminium matrix composites are produced using two different liquid metal infiltration methods, namely direct squeeze casting and gas pressure infiltration. Net-shape fibre performs for longitudinal parallel tensile bars are prepared by winding the Nextel™ 610 alumina fibre (3M, St Paul, MN) into graphite moulds. High purity aluminium, two binary (Al–6% Zn and Al–1% Mg) and one ternary (Al–6% Zn–0.5% Mg) aluminium alloys are used as matrix materials. The composite is tested in uniaxial tension–compression, using unload–reload loops to monitor the evolution of Young's modulus. A linear dependence between Young's modulus and strain is observed; this is attributed, by deduction, to intrinsic elastic non-linearity of the alumina fibre. This conclusion is then used to compare on the basis of the in situ matrix flow curve the influence of matrix composition and infiltration process on the composite stress–strain behaviour.     

Oxidation-induced microstructural changes of a polymer-derived Nextel™ 610 ceramic composite and impact on the mechanical performance

This study analyses the effects of heat treatments in oxidative atmosphere on the mechanical and microstructural properties of a fiber-reinforced weak interface composite (UMOX?) which is composed of a mullite-SiOC matrix and Nextel? 610 fibers with fugitive coatings. Composites of different porosity grades, depending on the polymer infiltration and pyrolysis cycle, are exposed to 1000 and 1200 °C for 50 h. The exposure provokes the formation of silica, which leads to matrix densification and the formation of silica bridges at the fiber–matrix interface, resulting in an increased interfacial bonding strength. Consequently, the fracture toughness and the flexural strength are significantly reduced. The study confirms that SiOC-based materials are suitable for an application at high temperatures in oxygen-rich atmospheres up to 1000 °C. It is, however, important to consider the microstructural changes and thereby induced decrease of the overall mechanical performance during a high-temperature use.     

Preparation of polycrystalline YAG/alumina composite fibers and YAG fiber by sol–gel method

Polycrystalline yttrium–aluminum garnet, Y₃Al₅O₁₂ (YAG) fiber and α-alumina and YAG matrix composite fiber were prepared by the sol–gel method. α-Alumina and YAG matrix composite fiber with fine and homogeneous microstructure could be successfully fabricated by interpenetrating YAG in alumina matrix and adding α-alumina of seed particles to fibers. Effect of α-alumina seed particles and YAG on crystallization and microstructure of composite fiber were discussed. The size of alumina matrix of the composite fibers heated at 1600°C for 4 h was below 2 μm. The tensile of strength alumina fiber heat-treated at 1500°C was 0.2 GPa, while that of the composite fiber was 1.1 GPa.     

Creep of Nextel™720/alumina–mullite ceramic composite at 1200 °C in air,argon, and steam

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 74.5 GPa and the ultimate tensile strength was 153 MPa. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. Primary and secondary creep regimes were observed in all tests. Creep run-out (set to 100 h) was achieved in laboratory air for creep stress levels ?91 MPa. The presence of either steam or argon accelerated creep rates and reduced creep lifetimes. Composite microstructure, as well as damage and failure mechanisms were investigated.     

The effect of notch depth on J-integral and critical fracture load in plates made of functionally graded aluminum–silicone carbide composite with U-notches under bending

The present paper deals with the effect of notch depth on J-integral and critical fracture load in a plate made of functionally graded aluminum–silicone carbide composite (Al–SiC) with U-notch under bending. The weight fraction of SiC particles varies from 0% to 20% through the specimen width. Using three criteria namely mean stress (MS), point stress (PS), and averaged strain-energy density (ASED), the critical fracture load has been predicted and its variation with respect to the notch depth has been studied. A comparison of the J-integral between functionally graded and homogeneous Al–SiC composite were made, where the notch tip in the functionally graded material is situated in a layer with same mechanical properties as the homogeneous composite. The results indicated that in the case where the notch scene is toward brittleness increment the critical J-integral in functionally graded material (FGM) is larger than that of in homogeneous material with the same mechanical properties at the notch tip. Therefore, FGM is more convenient than homogeneous material against fracture.     

Microstructure,mechanical properties and corrosion behaviour of Al–Si–Mg alloy matrix/zircon and alumina hybrid composite

In the present study, the effect of reinforcement on microstructure, mechanical properties and corrosion behaviour of aluminium–silicon–magnesium (Al–Si–Mg) alloy matrix hybrid composites reinforced with varying amounts of zircon and alumina has been investigated. Hardness and room temperature compressive tests were performed on Al–Si–Mg alloy as well as composites. Hardness and compressive strength was found to be higher for composites containing 3.75?% ZrSiO₄?+?11.25?% Al₂O₃. Similarly, Al–Si–Mg alloy and its composites were studied for corrosion behaviour in 1 N HCl corrosive media. The weight loss of all the composites was found to decrease with time due to the formation of passive oxide layer on the sample surface. The results obtained indicate that composites exhibit superior mechanical properties and corrosion resistance compared to unreinforced alloy.     

Mechanical properties and oxidation behaviors of carbon/carbon composites with C–TaC–C multi-interlayer

To improve the mechanical properties and oxidation-resistance properties, a C–TaC–C multi-interlayer structure was introduced in carbon/carbon (C/C) composites by chemical vapor infiltration. Compared with conventional C/C composites, a higher fracture toughness and strength have been achieved by using the C–TaC–C multi-interlayer. In addition, the composites also exhibit a higher preliminary oxidation temperature and a lower mass loss at high temperatures. The oxidation rate of the composites increases with temperature increasing in the range of 700–1300 °C, reaching a maximum value at 1300 °C, then decreases in 1300–1400 °C. A hexagonal structure of Ta₂O₅ phase is obtained when being oxidized at 700–800 °C, and it transforms to an orthorhombic phase at temperatures above 900 °C. The structures of C–TaC–C multi-interlayer are intact without cracks or porosities after being oxidized at 700–800 °C. In 900–1300 °C, the composites are oxidized uniformly with the formation of pores. At temperatures above 1300 °C, there are oxidation and non-oxidation regions with the oxidation process being controlled by diffusion.     

Processing and thermal stability of a Cfiber/SiCfiller/Si–C–Nmatrix composite: effect of oligomer vaporization and the surface oxide layer of SiC filler

The processing of carbon fiber-reinforced ceramic matrix composites (CMC) made by the precursor impregnation and pyrolysis (PIP) method was improved, and factors which deteriorate the thermal stability of the CMC were investigated. The processing time for cross-linking of a precursor polymer was substantially reduced by the application of a sealed metal container due to the suppression of the vaporization of oligomers. The strength of the as-fabricated CMC was 286 MPa and 77% of the original strength was retained after a heating at 1350 °C for 24 h in Ar. The reduction of the strength after the heating was due to the decomposition of SiO₂ which remained at the surface of the SiC filler particles. The decomposition reaction induced deterioration of carbon fibers and the matrix of the CMC at high temperature.     

Modeling quasi-static and high strain rate deformation and failure behavior of a (±45) symmetric E-glass/polyester composite under compressive loading

Quasi-static (1 × 10⁻³–1 × 10⁻² s⁻¹) and high strain rate (∼1000 s⁻¹) compressive mechanical response and fracture/failure of a (±45) symmetric E-glass/polyester composite along three perpendicular directions were determined experimentally and numerically. A numerical model in LS-DYNA 971 using material model MAT_162 was developed to investigate the compression deformation and fracture of the composite at quasi-static and high strain rates. The compressive stress–strain behaviors of the composite along three directions were found strain rate sensitive. The modulus and maximum stress of the composite increased with increasing strain rate, while the strain rate sensitivity in in-plane direction was higher than that in through-thickness direction. The damage progression determined by high speed camera in the specimens well agreed with that of numerical model. The numerical model successfully predicted the damage initiation and progression as well as the failure modes of the composite.     

Preparation and properties of fluorinated aliphatic alcohols/silica nanocomposites – Application to the encapsulation of anatase titanium oxide nanoparticles into these composite cores

A variety of fluorinated aliphatic alcohols [R_F-CH₂CH₂OH; R_F = CF₃(CF₂)₃CH₂(CF₂)₅, CF₃(CF₂)_n; n = 3, 5, 7] were applied to the preparation of the corresponding fluorinated alcohols/silica nanocomposites [R_F-CH₂CH₂OH/SiO₂] through the sol–gel reactions with tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions. R_F-CH₂CH₂OH/SiO₂ nanocomposites thus obtained have a good dispersibility and stability in not only water but also traditional organic solvents such as methanol, ethanol, 1,2-dichloroethane and tetrahydrofuran. FE–SEM (field emission scanning electron microscopy) and dynamic light scattering (DLS) measurements show that these composites are nanometer size-controlled fine particles in methanol. These fluorinated nanocomposites were also applied to the surface modification of glass to exhibit a superhydrophilic characteristic with a superoleophobicity on the modified surface. Interestingly, R_F-CH₂CH₂OH/SiO₂ nanocomposites were found to exhibit no weight loss behavior corresponding to the contents of the alcohols in the composites even after calcination at 800 °C. In addition, anatase TiO₂ nanoparticles (an-TiO₂) were effectively encapsulated into R_F-CH₂CH₂OH/SiO₂ nanocomposite cores under the similar sol–gel reactions to give the corresponding fluorinated alcohol/SiO₂/an-TiO₂ nanocomposites. These obtained nanocomposites can give a higher photocatalytic activity even after calcination at 1000 °C for the decolorization of methylene blue under UV light irradiation than that of the an-TiO₂ nanoparticles under the similar conditions, although the parent TiO₂ nanoparticles after calcination were unable to give a photocatalytic activity.     

Effect of accelerated aging on the viscoelastic properties of Elast-Eon™: A polyurethane with soft poly(dimethylsiloxane) and poly(hexamethylene oxide) segments

The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Elast-Eon? 3, (a polyurethane with poly(dimethylsiloxane) and poly(hexamethylamine oxide) segments) were investigated before and after the specimens had undergone accelerated aging in saline solution at 70 °C for 38, 76 and 114 days (to simulate aging at 37 °C, for 1, 2 and 3 years, respectively). All sets of specimens were immersed in physiological saline solution at 37 °C during testing and the properties were measured using dynamic mechanical analysis (DMA). A sinusoidal cyclic compression of 40 N ± 5 N was applied over a frequency range, f, of 0.02–100 Hz. Values of the storage, E′, and loss, E″, moduli were found to depend on f; the dependence of E′ or E″ on the logarithm (base 10) of f was represented by a second-order polynomial. After accelerated aging, the E′ and E″ increased significantly (p < 0.05) and the specimens became darker and more opaque. SEM images showed that accelerated aging affected the surface morphology but ATR-FTIR spectra did not show any appreciable change in surface chemistry. DSC thermograms showed some slight changes in thermal properties following accelerated aging.     

Process and mechanical properties of carbon/carbon–silicon carbide composite reinforced with carbon nanotubes grown in situ

A hierarchical C_f/C–SiC composite was fabricated via in situ growth of carbon nanotubes (CNTs) on fiber cloths following polymer impregnation and pyrolysis process. The effects of CNTs grown in situ on mechanical properties of the composite, such as flexural strength, fracture toughness, crack propagation behavior and interfacial bonding strength, were evaluated. Fiber push-out test showed that the interfacial bonding strength between fiber and matrix was enhanced by CNTs grown in situ. The propagation of cracks into and in fiber bundles was impeded, which results in decreased crack density and a “pull-out of fiber bundle” failure mode. The flexural strength was increased while the fracture toughness was not improved significantly due to the decreased crack density and few interfacial debonding between fiber and matrix, although the local toughness can be improved by the pull-out of CNTs.     

Formation and sintering of 75 mol% alumina/25 mol% zirconia (2–3.5 mol% yttria) composite powder prepared by the hydrazine method

Al₂O₃/Y₂O₃-doped ZrO₂ composite powders with 25 mol% ZrO₂ have been prepared by the hydrazine method. As-prepared powders are the mixtures of AlO (OH) gel solid solutions and amorphous ZrO₂. The formation process leading to -Al₂O₃/t-ZrO₂ composite powders is investigated. Hot isostatic pressing has been performed for 1 h at 1500 °C under 196 MPa. Dense ZrO₂-toughened Al₂O₃ (ZTA) ceramics with homogeneous-dispersed ZrO₂ particles show excellent mechanical properties. The toughening mechanism is discussed.     

Ablation characteristics of a 4D carbon/carbon composite under a high flux of combustion products with a high content of particulate alumina in a solid rocket motor北大核心CSCD

The ablation behavior of a four-directional carbon/carbon (C/C) composite was examined in a lab-scale solid rocket motor under a high flux of combustion products containing a high content of particulate alumina. The composite consisted of three braided carbon fiber bundles at 120 to each other in the XY plane and a hexagonal array of carbon rods in the Z direction, all in a pitch carbon matrix. The rods consisted of a unidirectional array of the same carbon fibers in a pitch carbon matrix The composite was placed in the rocket motor with its XY plane perpendicular to the gas flow and its ablation rate, ablation behavior and microstructure were investigated. The flow field of the combustion products was simulated by solving the Reynolds-averaged NavierStokes equations. A deep pit was formed on the surface of the composite, the center of which coincides with the simulated particle accumulation area. The mechanical erosion was significantly increased when the particle impact velocity exceeded 96. 82 m/s. The carbon rods were more susceptible to erosion than the surrounding fiber bundles. The maximum ablation rates of the carbon rod and bundles were increased almost by an order of magnitude by increasing the particle impact velocity by a factor of two. Numerous crater-like pores on the ends of the carbon rods were formed by alumina particle impaction, and the tips of the fibers in the carbon rods were almost flat and lower than the surrounding matrix. Heating caused by the particle impact increased the thermal oxidization and hence the overall ablation rate of the composite.     

Facile preparation of three-dimensional graphene oxide/ $${\iota}$$ ι -carrageenan composite aerogel and its efficient ability for selective adsorption of methylene blue

Journal of Materials Science - A three-dimensional graphene oxide/ $${\iota}$$ -carrageenan composite aerogel (GO/ $${\iota}$$ -Car) has been facilely manufactured in a benign approach and...     

Sol‒gel synthesis,properties and protein loading/delivery capacity of hollow bioactive glass nanospheres with large hollow cavity and mesoporous shell

Hollow nanospheres exhibit unique properties and find a wide interest in several potential applications such as drug delivery. Herein, novel hollow bioactive glass nanospheres (HBGn) with large hollow cavity and large mesopores in their outer shells were synthesized by a simple and facile one-pot ultrasound assisted sol‒gel method using PEG as the core soft-template. Interestingly, the produced HBGn exhibited large hollow cavity with ~43 nm in diameter and mesoporous shell of ~37 nm in thickness and 7 nm pore size along with nanosphere size around 117 nm. XPS confirmed the presence of Si and Ca elements at the surface of the HBGn outer shell. Notably, HBGn showed high protein loading capacity (~570 mg of Cyto c per 1 g of HBGn) in addition to controlled protein release over 5 d. HBGn also demonstrated a good in vitro capability of releasing calcium (Ca²⁺: 170 ppm) and silicate (SiO₄⁴⁻: 78 ppm) ions in an aqueous medium over 2 weeks under physiological-like conditions. Excellent in vitro growth of bone-like hydroxyapatite nanocrystals was exhibited by HBGn during the soaking in SBF. A possible underlying mechanism involving the formation of spherical aggregates (coils) of PEG was proposed for the formation process of HBGn.     

Preparation and characterization of the graphene–carbon nanotube/CoFe2O4/polyaniline composite with reticular branch structures

A novel graphene–carbon nanotube (graphene–CNT)/CoFe₂O₄/polyaniline composite with reticular branch structures had been fabricated by in situ chemical polymerization method. The textured structures of the as-prepared composites were characterized by the fourier transform infrared (FTIR) and X-ray diffraction (XRD). The morphology was analyzed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic properties were tested by vibrating sample magnetometer and four-probe conductivity tester. The results showed that the graphene–CNT/CoFe₂O₄/polyaniline composite had the unique reticular branch structures. When the mass ratio of the graphene–CNT/CoFe₂O₄ to aniline was 1:3, the magnetic saturation value of the composite achieved 39.6 emu g⁻¹, and the conductivity reached 1.957 S cm⁻¹. Based on the experimental results, a probable formation mechanism for the unique reticular branch structures was proposed.