All-poly(ethylene terephthalate) composites by film stacking of oriented tapes

Self-reinforced polymer or all-polymer composites have been developed to replace traditional fibre reinforced plastic (FRP) with good interfacial adhesion and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, all-PET composites were prepared by film stacking of oriented PET tapes. A processing temperature window was determined by a series of tests on PET tapes and co-PET films, including DSC and T-peel tests. Tensile properties of PET tape, co-PET film and all-PET composites are reported and compared with a commercial co-extruded PURE^® polypropylene tape. The effect of compaction temperatures and pressures on tensile properties of all-PET composites was investigated to explore the optimum processing parameters for balancing good interfacial adhesion between tapes and residual tensile properties of PET tapes.     

Microstructure and mechanical properties of short carbon fibre/SiC multilayer composites prepared by tape casting

Silicon carbide multilayer composites containing short carbon fibres (C_sf/SiC) were prepared by tape casting and pressureless sintering. The C fibres were dispersed in solvents with dispersant (Triton X-100) firstly and then mixed with the SiC slurry to make green C_sf/SiC tapes. Fibres were homogeneously distributed in the tape and tended to align fairly well along the tape casting direction. The addition of short C fibre hindered the shrinkage in the plane containing the fibres as well as the grain growth of SiC during sintering. The weight loss occurring during oxidation tests of C_sf/SiC multilayer composites increased with fibre amount and material porosity. Elastic modulus of C_sf/SiC multilayer composites decreased linearly with fibre amount. Bending strength presented clear relationship with the relative density, that is with the total porosity.     

On the green density, sintering behavior and electrical property of tape cast Ce0.9Gd0.1O1.95 electrolyte films

Gadolinia doped ceria (Ce_0.9Gd_0.1O_1.95, GDC) electrolyte films were tape cast from oxalate coprecipitated GDC powders, gelcast GDC powders and their mixtures, respectively, to evaluate the effects of the original particle size and distribution on the properties of the green and sintered GDC cast tapes. The apparent density of different original powders, as well as the green density, sintered behavior, and electrical conductivity of tapes cast from the various starting powders were investigated. Mixing the coprecipitated and the gelcast GDC powders not only results in a higher packing efficiency of particles in the loose powders, but also results in higher green and sintered densities of cast tapes. Furthermore, tapes cast from the 50/50 powder mixtures can be sintered to 96.2% of theoretical density at relatively low sintering temperature of 1400°C, whereas those from the oxalate coprecipitated and from the gelcast powders were only 89.7 and 94.1% dense, respectively. The ac impedance measurement shows that GDC films cast from the 50/50 powder mixture exhibit good electrical conductivity (4.2 and 6.0 S m⁻¹ at 700 and 800°C in air, respectively). The test results have revealed that high-density GDC films can be fabricated by tape casting technique at relatively low sintering temperature by optimizing the particle size distribution of the starting powders.     

Residual stress distribution in carbon fibre/thermoplastic matrix pre-impregnated composite tapes

The distribution of residual strain in carbon fibre (P75) reinforced thermo-plastic (polyetheretherketone, PEEK) composites has been studied by monitoring the Raman frequencies of the embedded carbon fibres at the microscopic level. The average longitudinal strain in the fibre measured in a 100 mm² section of a P75/PEEK prepreg was found to be compressive and comparable in magnitude to residual strain values computed analytically. The combined effects of differential thermal expansion of the two materials, differences in fibre size and in the thickness of resin layer, are offered as likely explanations for the incurred variations in the Raman frequency values and the considerable spread of the fibre Raman frequency distribution in the prepreg tape. Finally, it is demonstrated that the previously reported high values of apparent compressive strain in similar composite tapes by means of Raman spectroscopy were artefacts of the experimental procedure.     

Towards cost effective manufacturing of Ti/SiC fibre composites and components

Abstract

Titanium/silicon carbide fibre composites offer an excellent combination of weight specific properties and are ideal for many components in gas and steam turbine engines. However, potential industrial applications are hampered by the relatively high cost of the materials. This paper critically examines the characteristics of various manufacturing or processing routes for such composites, including well developed processes, such as foil–fibre–foil, physical vapour deposition, and vacuum plasma spraying, and new slurry powder metallurgy processes currently being developed. For a given manufacturing route, composite properties are enhanced if the material possesses uniform fibre distribution and a low oxygen content and is free from fibre/matrix interface reactions, residual voids, and fibre damage. The capabilities of the above processes in satisfying these requirements are compared and discussed. Possibilities of reducing product costs are analysed. Several ways of improving the cost effectiveness of mamifacturing such composites are outlined.     

Preparation of Aluminum Nitride Ceramics by Aqueous Tape Casting

High compacted aluminum nitride (AlN) substrates were prepared by aqueous tape casting. Aluminium dihydrogen phosphate was used to modify AlN particle surface from hydrolysis during casting process. The absolute value of zeta potential for the AlN particle treated by Al(H₂PO₄)₂ was 60mv at pH = 9. The slurry suitable for tape casting was prepared which possessed shear-thinning behavior and appropriate viscosity. The results showed that the green tapes own excellent properties including high bulk density, uniform pore distribution and low porosity. The samples were fired at 1700°C (lower than melting point of Pt) with pressureless sintering process which can be used to fabricate complex device.     

Preparation and microwave dielectric properties of multilayer Li1.075Nb0.625Ti0.45O3 co-fired ceramics with aqueous tape casting

Multilayer Li_1.075Nb_0.625Ti_0.45O₃ (LNT) ceramics for low temperature co-fired ceramic (LTCC) application were prepared by aqueous tape casting. The rheological test indicated that the aqueous slurries exhibited a typical shear-thinning behavior without thixotropy suitable for tape casting process. The green tapes with 2 wt% V₂O₅ addition have satisfactory mechanical properties. Scanning electron microscopy studies revealed that the green tapes have a smooth defect-free surface and that the sintered LNT ceramics have a fine grain microstructure with a uniform grain size. Therefore, aqueous tape casting is suitable for the manufacture of high performance multilayer LNT ceramics. Silver inner-electrode was sintered with LNT tapes at 900 °C, and no reaction been observed between LNT ceramic and sliver layers. The addition of V₂O₅ does not induce much degradation on the microwave dielectric properties. In the case of 2 wt% V₂O₅ addition, the ceramics show good microwave dielectric properties of ε _r  = 65, Q × f = 6,350 GHz. It represents that LNT ceramics could be promising for multilayer LTCC application.     

Review of current strategies to induce self-healing behaviour in fibre reinforced polymer based composites

Abstract

This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.     

Characterization of aluminium-matrix composites made by compocasting and its variations

Compocasting (semisolid-semisolid, SS) and its two variations: SL (semisolid-liquid) and LL (liquid-liquid) process routes are used to make 2024Al reinforced with 3 mm and 12 mm long FP-alumina fibres. Squeeze-casting is used as a complementary casting technique. The effect of processing route on microstructure and the mechanical properties of these composites is studied. The SS route produces composites with uniform fibre distribution, but casting is difficult due to the high viscosity of the slurry. The SL route gives good fibre distribution and the casting is easy. The LL route allows addition of a large amount of fibres but gives castings with a non-uniform fibre distribution, which lowers the failure strains and reduces the strength of the composites drastically. The addition of alumina fibres to 2024Al increases its modulus of elasticity considerably. The observed modulus values show good agreement with the theoretical predictions. The strength values are somewhat lower than the theoretical predictions. This is because the composites failed at strains slightly lower than the fibre failure strain. Absence of fibre pull-out indicates that a good fibre matrix bond has been produced in each case.     

Dispersion and rheological studies of Y-PSZ tape casting slurry

Different solvent systems in combination with three different dispersants were tried to find out the suitable solvent-dispersant combination, which give optimum dispersion of PSZ. Based on sedimentation, viscosity and rheology characteristics, zeotropic ethanol : xylene with a ratio of 50 : 50 along with 0.5 wt% phosphate ester was found to be the best solvent and dispersant combination. Optimized tape casting slurry was prepared using PEG 600 and BBP as plasticizers and PVB as the binder. Cyclohexanone was used as the homogenizer. The optimized slurry composition with 58% solid loading exhibited shear-thinning pseudoplastic rheological behaviour. Y-PSZ tapes of ∼ 50 Μm thickness free from visible defects were cast with a green tape density of 55%.     

Optimization of barium titanate nanopowder slip for tape casting

Dispersion of barium titanate nano powder of average particle size ∼30 nm in different solvent systems of tape casting (toluene–ethanol, methyl ethyl ketone–ethanol, xylene–ethanol) along with Triton x-100 or phosphate ester as dispersants has been studied using sedimentation experiments. The influence of different parameters such as type of solvent system, dispersant and concentration of dispersant on BaTiO₃ slip dispersion, viscosity and the properties of green tape were studied. The optimal concentration of dispersant was determined from the minimum slip viscosity. Xylene–ethanol with phosphate ester was found to be the best solvent and dispersant system for tape casting. Defect free, denser and smooth green tapes are formed with this system.     

A Dielectric Sensing Approach for Controlling Matrix Composition During Oxide-Oxide Ceramic Composite Processing

Continuous fiber reinforced ceramic matrix composites (CMC’s) made from aluminum oxide fibers and matrices are usually fabricated using a tape casting process. In this process, ceramic slurry consisting of the oxide powder, a polymeric binder and a solvent is infiltrated into a woven ceramic fiber mat. After evaporation of some of the solvent, the resulting flexible tapes can be stacked and sintered to create a composite component. Because the fraction of ceramic powder in the slurry can vary during processing, in-situ compositional sensors are required for on-line feedback control to limit property variations in the composite material. Since the dielectric properties of the slurry components are distinctly different, the effective permittivity of the slurry depends upon its composition. Here, a non-contact capacitance probe has been used to explore the possibility of capacitance sensing for compositional control. Results indicate that the removal of solvent during a precision drying step may be monitored by this approach. The feasibility of monitoring changes in the slurry’s composition during infiltration of the fiber mat is also discussed.     

Characteristics of CF/PEI tape winding process with on-line consolidation

The effects of processing conditions on consolidation quality for the tape winding process of thermoplastic composites with on-line consolidation have been investigated. Composite rings were manufactured using carbon fibre (CF)/polyetherimide (PEI) tape for both cases with and without an insulated ring. Based on heat transfer and intimate contact/autohesion mechanisms, a steady-state finite element method (FEM) model was developed to analyze consolidation quality and overheating in composite tapes. The processing windows with the upper bound for good consolidation and the lower bound for overheating were established for winding speed as a function of processing temperature, when the compaction pressure was kept constant. Good correlation was obtained between the steady-state FEM model and experimental data.     

Development of a powder coated fibre pre-processing route for production of fibre reinforced composites

Abstract

As a critical material for next generation aeroengines, fibre reinforced composites such as silicon carbide reinforced titanium continue to attract strong attention from both industrial and academic sectors. Reducing the processing costs and increasing component processing flexibility remain the priorities of current research. This paper presents a novel powder coated fibre pre-processing technique to meet such industrial requirements. The proposed technique is based on slurry powder metallurgy and presents itself as a cost effective alternative to current processing methods. It involves firstly, mixing matrix powder particles with an appropriate organic binder and solvent to form a slurry, drawing a continuous silicon carbide fibre through the slurry, drying the coated fibre and finally laying up the fibres into a composite preform for subsequent consolidation. The organic component is removed from the preform matrix via a binder burnout phase prior to composite consolidation.     

Zone refining of sintered,microwave derived YBCO superconductors

Post-sintering treatments, such as zone melting under a thermal gradient, have been conducted on sintered YBCO tape cast films. YBCO precursor powder was derived through decomposition of a mixture of nitrates of cations in a microwave oven for ~ 4 min. The resulting powder was characterized and made into thin sheets by tape casting and then sintered at 945 °C for 5 h. The sintered tapes were subjected to repeated zone refining operations at the relatively high speed of ~ 30 mm h^–1. A microstructure having uniformly orientated grains in thea-b plane throughout the bulk of the sample was obtained by three repeated zone refining operations. Details of precursor preparation, microwave processing and its advantages, zone refining conditions and microstructural features are presented in this paper.     

Application of alginate gelation to aqueous tape casting technology

This work deals with a novel forming process for manufacturing ceramic tapes in an aqueous medium, that combines tape casting and gel-casting technologies. Aqueous tape casting suspensions of Al₂O₃ are prepared to a solid loading of 57 vol.% (84 wt.%) by adding 15 wt.% of a binder system consisting of acrylic emulsions and a small concentration (≤0.5 wt.%) of alginate. The as-cast tape is immersed in a CaCl₂ solution and the alginate undergoes gelation. This allows releasing of the tape from the carrier film so that no sticking occurs and crack formation is avoided. Sintered densities are ∼97% of theoretical, similar to those obtained by conventional aqueous tape casting.     

Effect of type of solvent and dispersant on NANO PZT powder dispersion for tape casting slurry

Dispersion of PZT powder of average particle size 75 nm in commonly used solvent systems for tape casting namely, toluene-ethanol and MEK-ethanol (azeotropic), xylene-ethanol (zeotropic) along with triton x-100, menhaden fish oil and phosphate ester as dispersants has been studied using simple sedimentation experiments. The relative merits of these three solvent systems and dispersants in dispersing PZT powder was analyzed. In all the three solvent systems, phosphate ester was found to be the best dispersant. Xylene-ethanol with phosphate ester gave the excellent dispersion characteristics for nano-PZT powder. The results of initial dispersion studies were confirmed by the formation of defect free, denser and smooth green tapes using xylene-ethanol and phosphate ester, while the other two solvent systems gave defective green tapes. The influence of phosphate ester on dispersion is explained by the dissociation and ionization, and the dominance of electrostatic repulsion even though organic solvent systems were used.     

Fabrication of alumina short fibre reinforced aluminium alloy via centrifugal force infiltration

Abstract

A new casting process for fabricating short fibre reinforced metal matrix composites via the centrifugal force infiltration of fibre preforms with molten aluminium alloys is described. The effect of processing variables, such as pouring temperature, preheated mould temperature, and time of application of centrifugal force, on the infiltration kinetics and resultant microstructure is discussed. Composites having fibre volume fractions of 4·5, 8·0, 12, and 16% were obtained via this method. Comparisons with existing infiltration technology and the mechanical properties of the composite are presented.

MST/2000     

层状Al2O3-TiC复相陶瓷的制备与性能

利用流延到工艺制备了Ａｌ２Ｏ３－ＴｉＣ复相陶瓷薄膜，通过叠层，预压，脱粘和热压烧结工工艺，制行了层状结构复相陶瓷，讨论了分散剂，ｐＨ值，固含量对浆粘粘度的影响，用ＴＧＡ分析了陶瓷膜的脱粘过程，用ＳＥＭ和光学显微镜分析了素坯膜的微观形貌和材料在压力作用下裂纹扩展情况，由于裂纹沿弱界面扩散应力松弛，有效地提高了材料的断裂韧性和断裂功，为陶瓷的结构设计提供了一条新思路。     

Effects of fibre surface silanisation on silica fibre/phenolics composites produced by resin transfer moulding process

Abstract

The effects of fibre surface silanisation on silica fibre/phenolics composites produced by the resin transfer moulding (RTM) solution impregnation route were investigated. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and micro-Wilhelmy method were used to evaluate the surface properties of silanised silica fibre. The interlaminar shear strength (ILSS) measurements and morphological observations of the silica fibre/phenolics composites were also performed. The interactions occurring between silica fibre and the components of phenolic resin solution affect the dynamic adsorption behaviour of phenolic resin onto fibre reinforcement. The competitive adsorption of ethanol as solvent onto silica fibre suppresses that of phenolic resin. Fibre surface silanisation by γ-aminopropyl-triethoxysilane (γ-APS), γ-glycidoxypropyl-trimethoxysilane (γ-GPS) and γ-methacryloxypropyl-trimethoxysilane (γ-MPS) leads to the improvement of mechanical interfacial properties of silica fibre/phenolics composites on one hand and decreases the inhomogeneities of resin distribution and mechanical interfacial properties at different regions of the RTM product on the other hand.