Showing papers on "Ceramic matrix composite published in 2006"

Manufacturing technology for aerospace structural materials

Abstract: Introduction Aluminium Magnesium & Beryllium Titanium High Strength Steels Superalloys Polymer Matrix Composites Adhesive Bonding and Integrally Cocured Structure Metal Matrix Composites Ceramic Matrix Composites Structural Assembly Appendix A: Metric Conversions Appendix B: Brief Review of Materials Fundamentals

A review of the development of three generations of small diameter silicon carbide fibres

Abstract: Three generations of small diameter ceramic fibres based on polycrystalline silicon carbide have been developed over a period of thirty years. This has been possible due to studies into the relationships between the microstructures and properties of the fibres. A variety of techniques have been employed by research teams on three continents. The fibres are made by the conversion of polymer precursors to ceramic fibres and all three generations are presently produced commercially. The nature of the precursor and the techniques used for cross-linking have been varied in order to optimise both properties and cost of manufacture. It has been possible to improve the characteristics of the fibres as the processes involved in the cross-linking of the precursor fibres have been better understood and the mechanisms governing both room temperature and high temperature behaviour determined. The result is that, although first generation fibres were limited by a low Young's modulus at room temperature and by creep and instability of the structure at temperatures far lower than those limiting the behaviour of bulk silicon carbide, the third generation fibres shows many of the characteristics of stoichiometric silicon carbide. This remarkable improvement in characteristics has been due to a thorough understanding of the materials science governing the behaviour of these fibres which are reinforcements for ceramic matrix composite materials.

New double-ceramic-layer thermal barrier coatings based on zirconia–rare earth composite oxides

Abstract: A series of La 2 O 3 –ZrO 2 –CeO 2 composite oxides were synthesized by solid-state reaction The final product keeps fluorite structure when the molar ratio Ce/Zr ≥ 07/03, and below this ratio only mixtures of La 2 Zr 2 O 7 (pyrochlore) and La 2 O 3 –CeO 2 (fluorite) exist Averagely speaking, the increase of CeO 2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La 2 (Zr 07 Ce 03 ) 2 O 7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering Based on the large thermal expansion coefficient of La 2 Ce 325 O 95 , the low thermal conductivities and low sintering abilities of La 2 Zr 2 O 7 and La 2 (Zr 07 Ce 03 ) 2 O 7 , double-ceramic-layer thermal barrier coatings were prepared The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings

Oxidation of Zirconium Diboride–Silicon Carbide at 1500°C at a Low Partial Pressure of Oxygen

Abstract: The oxidation behavior of zirconium diboride containing 30 vol% silicon carbide particulates was investigated under reducing conditions. A gas mixture of CO and ∼350 ppm CO2 was used to produce an oxygen partial pressure of ∼10−10 Pa at 1500°C. The kinetics of the growth of the reaction layer were examined for reaction times of up to 8 h. Microstructures and chemistries of reaction layers were characterized using scanning electron microscopy and X-ray diffraction analysis. The kinetic measurements, the microstructure analysis, and a thermodynamic model indicate that oxidation in CO–CO2 produced a non-protective oxide surface scale.

Preparation and Microstructure of Multi‐Wall Carbon Nanotubes‐Toughened Al2O3 Composite

Abstract: With multi-wall carbon nanotubes (MWNTs) as reinforcement, a 12 vol% MWNTs/alumina (Al2O3) ceramic composite was obtained by hot pressing. A fracture toughness of 5.55±0.26 MPa·m1/2, 1.8 times that of pure Al2O3 ceramics, was achieved. Experimental results showed that the enveloping of carbon nanotubes (CNTs) with sodium dodecyl sulfate (SDS) is effective in changing the hydrophobicity of CNTs to hydrophilicity and improving the dispersion of CNTs in aqueous solution. Enveloped with SDS, CNTs can be homogeneously mixed with Al2O3 at a microscopic level by heterocoagulation. This mixing method can obviously improve the chemical compatibility between CNTs and Al2O3, which is important for enhancement of interfacial strength between them.

Phosphor in Polycrystalline Ceramic Structure and a Light-Emitting Element Comprising Same

Abstract: The invention relates to a phosphor in a polycrystalline ceramic structure and a light-emitting element provided with the same comprising a Light-Emitting Diode (LED) in which a composite structure of phosphor particles is embedded in a matrix, characterized in that the matrix is a ceramic composite structure comprising a polycrystalline ceramic alumina material, hereafter called luminescent ceramic matrix composite. This luminescent ceramic matrix composite can be made by the steps of converting a powder mixture of ceramic phosphor particles and alumina particles into a slurry, shaping the slurry into a compact, and applying a thermal treatment, optionally in combination with hot isostatic pressing into a polycrystalline phosphor-containing ceramic alumina composite structure. The luminescent ceramic matrix composite further allows a method of tuning the light-diffusing properties by changing at least one of the fractions of phosphor particles and second ceramic particles, the grain size of the particles of the ceramic composite structure, the difference in the refractive index of the particles of the ceramic composite structure, and the porosity in the polycrystalline phosphor-containing ceramic composite structure.

Development of CNT/Si3N4 composites with improved mechanical and electrical properties

Abstract: Silicon nitride based composites with different amount (1, 3 or 5 wt%) of carbon nanotubes have been prepared by using hot isostatic pressing. Composites with 1, 5 or 10 wt% carbon black and graphite have been manufactured, in comparison. Optimisation of the manufacturing processes has been performed, providing intact carbon nanotubes during high temperature sintering. In the case of 1 or 3 wt% carbon nanotube addition, the increase of gas pressure during sintering resulted in an increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements. Scanning electron microscopy showed that carbon nanotubes have a good contact to the surface of silicon nitride grains. The electrical properties of silicon nitride matrices with carbon addition may change essentially.

Bioceramic composite coatings and process for making same

Abstract: The present invention discloses novel polymer-ceramic matrix composites and processes for making same. The composites can be used in biomedical applications, in particular, coatings of implants and other medical devices, where both the ceramic phase and the polymer phase are bio-compatible. The composites combine a reinforcing polymer phase with a continuous ceramic matrix to create materials with properties that are new and superior to polymer or ceramic phases alone. The composites can incorporate a bioactive agent.

Ceramic matrix composite vane with chordwise stiffener

Abstract: A means (22) for structurally stiffening or reinforcing a ceramic matrix composite (CMC) gas turbine component, such as an airfoil-shaped component, is provided. This structural stiffening or reinforcing of the airfoil allows for reducing bending stress that may be produced from internal or external pressurization of the airfoil without incurring any substantial thermal stress. The stiffener is disposed on a CMC wall and generally extends along a chord length of the airfoil.

Bioactive ceramic coatings containing carbon nanotubes on metallic substrates by electrophoretic deposition

Abstract: A range of potentially bioactive ceramic coatings, based on combinations of either hydroxyapatite (HA) or titanium oxide nanoparticles with carbon nanotubes (CNTs), have been deposited on metallic substrates, using electrophoretic deposition (EPD). Sol–gel derived, ultrafine HA powders (10–70 nm) were dispersed in multi-wall nanotube-containing ethanol suspensions maintained at pH = ∼3.5 and successfully coated onto Ti alloy wires at 20 V for 1–3 min For TiO2/CNT coatings, commercially available titania nanopowders and surface-treated CNTs in aqueous suspensions were co-deposited on stainless steel planar substrates. A field strength of 20 V/cm and deposition time of 4 min were used working at pH = 5. Although the co-deposition mechanism was not investigated in detail, the evidence suggests that co-deposition occurs due to the opposite signs of the surface charges (zeta potentials) of the particles, at the working pH. Electrostatic attraction between CNTs and TiO2 particles leads to the creation of composite particles in suspension, consisting of TiO2 particles homogenously attached onto the surface of individual CNTs. Under the applied electric field, these net negatively charged “composite TiO2/CNT” elements migrate to and deposit on the anode (working electrode). The process of EPD at constant voltage conditions was optimised in both systems to achieve homogeneous and reasonably adhered deposits of varying thicknesses on the metallic substrates.

Carbon nanotube-ceramic composites

Abstract: The effective utilization of CNTs in composite application depends strongly on the ability to disperse CNTs homogeneously throughout the matrix and the interfacial combination is necessary for improving the CNT-based composite properties. In our work, we used surfactant and acid treatment to modify the CNTs surface and then incorporated the functionalized CNTs into various ceramic matrices including oxide and nitride ceramics. The fabrication of ceramic nanoparticle-immobilized CNTs not only improves the homogeneous distribution of CNTs in the ceramic matrices, but also makes the combination between two phases more tight. Mechanical property measurements clealy reveal obvious enhancement confirming the fabrication of true CNT-based composite materials with improved toughness properties. The addition of 0.1 wt% CNTs in the alumina increased the fracture toughness by about 1.6 times from 3.7 to 4.9 MPa.m1/2. For 1 wt% CNTs/BaTiO3composite, the toughness value (1.65 MPa.m1/2) is about 2.4 times than that of pure BaTiO3(0.68 MPa.m1/2). For 5 wt% CNTs/TiN composite, the fracture toughness is 3.81 MPa.m1/2, which is about 1.6 times than that of pure TiN ceramic whose toughness is 2.45 MPa . m1/2.

Microstructure and properties of spark plasma-sintered ZrO2-ZrB2 nanoceramic composites

Abstract: In a recent work,1 we have reported the optimization of the spark plasma sintering (SPS) parameters to obtain dense nanostructured 3Y-TZP ceramics. Following this, the present work attempts to answer some specific issues: (a) whether ZrO2-based composites with ZrB2 reinforcements can be densified under the optimal SPS conditions for TZP matrix densification (b) whether improved hardness can be obtained in the composites, when 30 vol% ZrB2 is incorporated and (c) whether the toughness can be tailored by varying the ZrO2–matrix stabilization as well as retaining finer ZrO2 grains. In the present contribution, the SPS experiments are carried out at 1200°C for 5 min under vacuum at a heating rate of 600 K/min. The SPS processing route enables retaining of the finer t-ZrO2 grains (100–300 nm) and the ZrO2–ZrB2 composite developed exhibits optimum hardness up to 14 GPa. Careful analysis of the indentation data provides a range of toughness values in the composites (up to 11 MPa·m1/2), based on Y2O3 stabilization in the ZrO2 matrix. The influence of varying yttria content, t-ZrO2 transformability, and microstructure on the properties obtained is discussed. In addition to active contribution from the transformation-toughening mechanism, crack deflection by hard second phase brings about appreciable increment in the toughness of the nanocomposites.

Laminated ceramic structures from oxide systems

Abstract: In this paper we present the results recently obtained in the study of laminated ceramic composites The motivation for studying and producing laminated ceramic composites have been illustrated Theoretical model useful to guide the design of laminated structures have been discussed and a route to prepare layered structures in the system Al 2 O 3 -ZrO 2 have been suggested The residual stresses developed in the ceramic layers have been quantified by indentation technique and piezo-spectroscopic analysis With the latter technique also the stress distribution in the different layers has been assessed Higher wear resistance under sliding and abrasive conditions of layered ceramics have been demonstrated The improvement of fatigue contact damage resistance and an increase of Weibull modulus underlined

Pyrolysis of Highly Metallized Polymers: Ceramic Thin Films Containing Magnetic CoFe Alloy Nanoparticles from a Polyferrocenylsilane with Pendant Cobalt Clusters

Abstract: We describe the pyrolysis of a highly metallized polymer precursor comprised of a polyferrocenylsilane with pendant cobalt clusters under a reductive atmosphere (N2/H2 = 92%/8%) leading to CoFe magnetic alloy nanoparticle-containing ceramic thin films. Variation of the pyrolysis conditions leads to changes in the nanoparticle size, size distribution, and composition, as well as the ceramic film structure, all of which influence the magnetic properties of the material. When pyrolyzed at 500 °C, the nucleation and growth afford uniform size, larger CoFe nanoparticles on the film surface, and smaller nanoparticles in the underlying layer of the ceramic films. We found that the SiC/C ceramic matrix prevents oxidation of fully embedded nanoparticles, whereas the surface nanoparticles are oxidized on exposure to air. The nanoparticle-containing films are superparamagnetic when pyrolyzed at 600 °C and are ferromagnetic at higher pyrolysis temperatures. The CoFe nanoparticle-containing ceramic thin films have bee...

Comparison among different sintering routes for preparing alumina-YAG nanocomposites

Abstract: Al2O3-YAG (50 vol.%) nanocomposite powders were prepared by wet-chemical synthesis and characterized by DTA-TG, XRD and TEM analyses. Amorphous powders were pre-heated at different temperatures (namely 600 °C, 800 °C, 900 °C and 1215 °C) and the influence of this thermal treatment on sintering behavior, final microstructure and density was investigated. The best performing sample was that pre-calcined at 900 °C, which yields dense bodies with a micronic/slightly sub-micronic microstructure after sintering at 1600 °C. A pre-treatment step to induce controlled crystallisation of the amorphous powder as well as a fast sintering procedure for green compacts, were also performed as a comparison. Finally, the previously stated thermal pre-treatment of the amorphous product was coupled to an extensive mechanical activation performed by wet planetary/ball milling. This procedure was highly effective in lowering the densification temperature, so that fully dense Al2O3-YAG composites, with a mean grain size smaller than 200 nm, were obtained by sintering in the temperature range 1370–1420 °C.

Prosthetic dental device

Abstract: A prosthetic dental device comprised of a composite material including a polymer material and a ceramic material mixed within the polymer material. In one embodiment, the ceramic fillers are substantially, homogeneously dispersed within the polymer material. In one embodiment, the ceramic material is bonded to the polymer material through a coupling agent. In addition, the prosthetic dental device can be comprised of a different composite material. This composite material includes a ceramic matrix having pores and an organic material infiltrated into the pores. To construct the ceramic matrix, ceramic particles, a binder material, and a porogen material are mixed to create a composite material which is then molded and heated to create a substantially rigid ceramic structure. At least some of the binder material and the porogen material are evaporated during the heating step to create pores in the matrix which are filled with the organic material.

Ceramic matrix composites : microstructure, properties and applications

Abstract: Part 1 Fibre, whisker and particulate-reinforced ceramic composites: Fibrous monolithic ceramics Whisker reinforced silicon nitride ceramics Fibre reinforced glass/glass-ceramic matrix composites Particulate composites. Part 2 Graded and layered composites: Functionally-graded ceramic composites SiAlON based functionally graded materials Design of tough ceramic laminates by residual stresses control Hardness of multilayered ceramics. Part 3 Nanostructured ceramic composites: Nanophase ceramic composites Nanostructured coatings on advanced carbon materials Processing and microstructural control of metal reinforced ceramic matrix nanocomposites Carbon nanotubes-ceramic composites Machinable nanocomposite ceramics. Part 4 Refractory and speciality ceramic composites: Magnesia-spinel (MgAl2O4) composite refractory materials Thermal shock of ceramic matrix composites Superplastic ceramic composites. Part 5 Non-oxide ceramic composites: Sialons Carbon-ceramic alloys Silicon nitride and silicon carbide-based ceramics Oxynitride glasses-glass ceramics Functionally graded ceramics.

Creep and Stress–Strain Behavior after Creep for SiC Fiber Reinforced, Melt-Infiltrated SiC Matrix Composites

Abstract: Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated silicon were subjected to creep at 1315°C at three different stress conditions. For the specimens that did not rupture after 100 h of tensile creep, fast-fracture experiments were performed immediately following the creep test at the creep temperature (1315°C) or after cooling to room temperature. All specimens demonstrated excellent creep resistance and compared well to the creep behavior published in the literature on similar composite systems. Tensile results on the after-creep specimens showed that the matrix cracking stress actually increased, which is attributed to stress redistribution between composite constituents during tensile creep.

電子線照射不融化によるポリカルボシランからの高性能 SiC 繊維の開発 (総説)

Abstract: Low-oxygen-content Si-C fibers (Hi-Nicalon) with 0.5 wt% oxygen were prepared from polycarbosilane with electron beam irradiation curing and pyrolysis. The thermal stability of the Hi-Nicalon fibers was significantly improved compared to Si-C-O fiber (Nicalon) with 12 wt% oxygen. However, creep deformation occurred in the Hi-Nicalon fiber at high temperatures, caused by SiC micro crystals and amorphous carbon. Then, stoichiometric and highly crystalline SiC fiber (Hi-Nicalon type S) was prepared from EB irradiation cured fiber by pyrolysis in a hydrogen gas flow. Type S fibers had high tensile modulus, excellent thermal stability, and creep resistance at high temperature. Hi-Nicalon and Hi-Nicalon type S fiber appear to be the best candidates for the reinforcement of ceramic matrix composites.

Processing and Mechanical Properties of Boron Carbide-Titanium Diboride Ceramic Matrix Composites

Abstract: The objective of the present investigation was to study the effect of TiB2 addition on sintering behavior and mechanical properties of pressureless-sintered B4C ceramic. Different amounts of TiB2, mainly 5 t0 30 wt.% were added to the base material. Pressureless sintering was conducted at 2,050 and at 2,150 °C. Addition of 30 wt.% TiB2 and sintering at 2,150 °C resulted in improving the density of the samples to about 99% of theoretical density. The composite samples exhibited very good mechanical properties (hardness, flexural strength and fracture toughness). As the amount of TiB2 was increased further, the mechanical properties were reduced, except for the fracture toughness, apparently due to too much TiB2 in the specimen.

Design and production of ceramic laminates with high mechanical reliability

Abstract: A procedure for designing innovative ceramic laminates characterized by high mechanical reliability is proposed in this work. A fracture mechanics approach has been considered to define the stacking sequence, thickness and composition of the different laminae on the basis of the requested strength and of the defect size distribution. Once the different laminae are stacked together a residual stress profile is generated upon cooling after sintering because of the differential thermal expansion coefficient. Such residual stress profile is conceived in order to allow stable growth of surface defects upon bending and guarantee limited strength scatter. As an example, the proposed approach is used to design and produce ceramic laminates in the alumina–zirconia and alumina–mullite system. Mechanical performances of the produced materials are discussed in terms of the generated residual stress profile and compared to parent monolithic ceramics.

Fabrication technologies for oxide–oxide ceramic matrix composites based on electrophoretic deposition

Abstract: Electrophoretic deposition (EPD) was used to fabricate alumina matrix composites with high volume fraction of woven fibre mat (Nextel™ 720) reinforcement in a multilayer structure. Colloidal suspensions of Al2O3 nanoparticles in ethanol medium with addition of 4-hydrobezoic acid were used for EPD. Two different techniques were developed for fabrication of Al2O3 matrix/Nextel™ 720 fibre composites. The first method is a combination of standard EPD of single fibre mats with a subsequent lamination procedure to fabricate the multilayered composite. The second method involves the simultaneous infiltration of several (three or more) Nextel™ 720 fibre mats by EPD in a tailor-made cell. The composites exhibit a homogeneous matrix microstructure, characterised by a very high particle packing density and relatively low porosity after sintering at 1300 °C. The EPD cell allows production of relatively large bodies (10 cm diameter). By combination of the multilayer EPD infiltration and lamination processes developed here, thick ceramic matrix composite components (>10 mm thickness) can be fabricated, which opens the possibility of greater industrial application of the materials.

Fabrication of structure-controlled hydroxyapatite/zirconia composite

Abstract: The structure-controlled hydroxyapatite/zirconia (HAp/ZrO 2 ) composites were fabricated. At first, cylindrical hydroxyapatite (HAp) samples were prepared by the extrusion process, and then the extruded HAp cylindrical samples were coated with 3 mol% of Y 2 O 3 partially stabilized ZrO 2 slurry, dried and aligned unidirectionally to form a composite bulk. The volume fraction of ZrO 2 in the HAp/ZrO 2 composite was estimated to be about 23 vol%. Bulk density and bending strength of the composites increased with sintering temperature. Fracture energy of HAp/ZrO 2 composite sintered at 1350 °C was approximately 1.6 times higher than that of monolithic HAp. Although the bending strength of HAp/ZrO 2 composite prepared in this study was relatively low, it exhibited high fracture energy than HAp monolithic and a non-brittle fracture behavior was obtained without using fiber as the reinforcement.