Showing papers on "Ceramic matrix composite published in 2007"

Evolution of structure during the oxidation of zirconium diboride–silicon carbide in air up to 1500 °C

Abstract: The structures that developed as dense ZrB2–SiC ceramics were heated to 1500 °C in air were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. The oxidation behavior was also studied using thermal gravimetric analysis (TGA). Below 1200 °C, a protective B2O3-rich scale was observed on the surface. At 1200 °C and above, the B2O3 evaporated and the SiO2-rich scale that formed was stable up to at least 1500 °C. Beneath the surface, layers that were rich in zirconium oxide, and from which the silicon carbide had been partially depleted, were observed. The observations were consistent with the oxidation sequence recorded by thermal gravimetric analysis.

Fabrication of Functionally Graded and Aligned Porosity in Thin Ceramic Substrates With the Novel Freeze–Tape-Casting Process

Abstract: Functionally graded and continuously aligned pore structures have been fabricated by a modified tape-casting process for use as solid oxide fuel cell electrodes, catalysts, sensors, and filtration/separation devices. Pore gradients from <5 to 100 μm and aligned pore tubules have been directly fabricated in various ceramic materials with thin substrate sections approximately 500-1500 μm utilizing both low-toxicity aqueous-based slips and organic solvents. This process allows for the generation of pores without the use of thermally fugitive pore formers in a single processing step with no need for tape lamination. The incorporation of tape casting, unidirectional solidification, and the freeze-drying process results in uniformly acicular pores aligned with the direction of the moving carrier film. Processing and microstructure variability will be discussed as it pertains to the effects of solids loading, freezing temperatures, and solvent type. Applications for this ceramic processing technology will also be discussed.

Pressureless Sintering of ZrB2–SiC Ceramics

Abstract: A pressureless sintering process was developed for the densification of zirconium diboride ceramics containing 10-30 vol% silicon carbide particles. Initially, boron carbide was evaluated as a sintering aid. However, the formation of a borosilicate glass led to significant coarsening, which inhibited densification. Based on thermodynamic calculations, a combination of carbon and boron carbide was added, which enabled densification (relative density > 98%) by solid-state sintering at temperatures as low as 1950°C. Varying the size of the starting silicon carbide particles allowed the final silicon carbide particle morphology to be controlled from equiaxed to whisker-like. The mechanical properties of sintered ceramics were comparable with hot-pressed materials with Vickers hardness of 22 GPa, elastic modulus of 460 GPa, and fracture toughness of ∼4 4 MPa· m 1/2 . Flexure strength was ∼ 460 MPa, which is at the low end of the range reported for similar materials, due to the relatively large size (∼ 13 μm long) of the silicon carbide inclusions.

Processing and Mechanical Properties of Zirconium Diboride-Based Ceramics Prepared by Spark Plasma Sintering

Abstract: Zirconium diboride (ZrB2) reinforced by nano-SiC whiskers has been prepared by spark plasma sintering (SPS). Of most interest is the densification of ZrB2–SiCw composites accomplished by SPS at a temperature as low as 1550°C. The relative density of ZrB2–SiCw composites could reach to 97% with an average grain size of 2–3 μm. Both flexural strength and fracture toughness of the composites were improved with increasing amount of SiCw. Flexural strengths ranged from 416 MPa for monolithic ZrB2 to over 545 MPa for ZrB2–15 vol% SiCw composites. Similarly, fracture toughness also increased from 5.46 MPa·m1/2 to more than 6.81 MPa·m1/2 in the same composition range. The relative density of ZrB2–SiCw composites could be further improved to near 100% by adding some sintering aids such as AlN and Si3N4; however, the effects of different sintering additives on the mechanical properties of the composites were different.

Fabrication and properties of reactively hot pressed ZrB2–SiC ceramics

Abstract: ZrB2–SiC ceramics with relative densities >99% were fabricated by ‘in situ’ reactive hot pressing from ZrH2, B4C and Si. The reaction was studied using two processes, (1) powder reactions at temperatures from 1150 to 1400 °C and (2) reactive hot pressing between 1600 and 1900 °C. The products from the reaction of a 2ZrH2:1B4C:1Si molar mixture were ZrB2, SiC, ZrO2 and ZrC. Modification of the composition to 2ZrH2:1.07B4C:1.16Si resulted in the elimination of the undesired ZrO2 and ZrC phases. The final composition was approximately ZrB2–27 vol% SiC with no undesired phases detected by X-ray diffraction, and only low concentrations of B4C detected by scanning electron microscopy. Elimination of the undesired phases was accomplished by removing surface oxides through chemical reactions at elevated temperatures. Reactively hot pressed samples consisting of ZrB2 with 27 vol% SiC had a Young's modulus of 508 GPa, a flexure strength of 720 MPa, a fracture toughness of 3.5 MPa m1/2 and a Vickers’ hardness of 22.8 GPa.

Self-healing mechanisms of a SiC fiber reinforced multi-layered ceramic matrix composite in high pressure steam environments

Abstract: Non-oxide ceramic matrix composites are potential candidates to replace the current nickel-based alloys for a variety of high temperature applications in the aerospace field. The durability of a SiC ( f ) /PyC ( i ) /[Si,C,B] ( m ) composite with a sequenced self-sealing matrix and Hi-Nicalon fibers was investigated at 600 °C for exposure durations up to 600 h. The specimens are aged in a variety of slow-flowing air/steam gas mixtures and total pressures, ranging from atmospheric pressure with a 10–50% water vapor content to 1 MPa with 10–20% water vapor content. The degradation of the composite was determined from the measurement of residual strength and strain to failure on post-exposure specimens and correlated with microstructural observations, weight changes and characterizations of the generated oxides. All of the post-exposure characterizations demonstrate the ability of the sequenced [Si,C,B] matrix to protect the PyC interphase from environmental attacks. Two different oxidation modes of the matrix, depending on the total pressure are discussed in terms of the reactivity of the boron-containing layers, and their relative positions in the sequenced matrix. In high pressure environments, a strong localized dissolving of a small amount of SiC fibers in the boria-containing oxide is evidenced at 600 °C.

Ceramic matrix composite turbine engine vane

Abstract: A vane has an airfoil shell and a spar within the shell. The vane has an outboard shroud at an outboard end of the shell and an inboard platform at an inboard end of the shell. The shell includes a region having a depth-wise coefficient of thermal expansion and a second coefficient of thermal expansion transverse thereto, the depth-wise coefficient of thermal expansion being greater than the second coefficient of thermal expansion.

Zirconia Transport by Liquid Convection during Oxidation of Zirconium Diboride–Silicon Carbide

Abstract: During high-temperature oxidation of ZrB2–SiC composites, a multi-layer oxide scale forms with a silica-rich borosilicate liquid as the surface oxide layer. Here, a recently proposed novel mechanism for the high-temperature oxidation of ZrB2–SiC composites is further investigated and verified. This mechanism involves the formation of convection cells in the oxide surface layer during high-temperature oxidation of the composite. The formation of zirconia deposits found in the center of the convection cells is proposed here to be the consequence of liquid transport. The nature and deposition mechanism of the zirconia is reported in detail, using calculated phase equilibrium diagrams and microstructure observations of a ZrB2-15 vol% SiC composite tested at 1550° and 1700°C in ambient air for various times. The calculated phase equilibrium diagrams for the binary ZrO2–B2O3 system as well as the ternary B2O3–SiO2–ZrO2 system at 1500°C are reported here to interpret these results.

Mechanical properties of SiC composites incorporating SiC-coated multi-walled carbon nanotubes

Abstract: Multi-walled carbon nanotubes (MWCNTs) were coated with a nanometer-sized SiC polycrystalline layer by the reaction of SiO(g) and CO(g). Nanometer-sized SiC powders were mixed with 1–5 vol% SiC-coated MWCNTs and successfully sintered at 1800 °C by means of pulsed electric current sintering. These composites showed superior microhardness of 30.6 GPa and toughness of 5.4 MPa m 1/2 compared to monolithic SiC ceramics due to the improvement of adhesion between MWCNTs and the SiC matrix by the SiC coating. The microhardness and toughness of the monolithic SiC ceramics are 25.5 GPa and 4.8 MPa m 1/2 , respectively. The SiC-coated MWCNTs/SiC composites showed an interesting behavior with the elastic recovery when undergoing an indentation test.

Field assisted sintering of electro-conductive ZrO2-based composites

Abstract: In order to reveal the fundamentals of the field assisted sintering technique (FAST), also known as spark plasma sintering (SPS), the evolution of the current density and temperature distribution in the punch-die-sample set-up during FAST of ZrO2–TiN powder mixtures was modeled by finite element calculations supported by in situ measured electrical and thermal input data. The thermal and electrical properties of partially sintered composite powder compacts were estimated using theoretical mixture rules, allowing to calculate the current density and temperature distribution inside the tool and the specimen during the FAST sintering process. The electrical properties of the sintering composite powder compact, and hence the thermal distribution in the sinter set-up, changed drastically during densification once percolation occurred. Based on the calculated thermal distribution inside the composite powder compact, an optimal tool-powder compact design was determined in order to process electrically conductive ZrO2–TiN composites from electrical insulating powder compacts within minutes with high reproducibility.

Multilayer ceramic composites with high failure resistance

Abstract: Since Clegg et al. first fabricated SiC/C multilayer composites in 1990, multilayer ceramics have received much attention because of their improved properties achieved by designing weak interfaces. The weak interface can deflect the crack propagating perpendicularly to the plane of laminates repeatedly during fracture, thus leading to extremely high work-of-fracture. In this work multilayer composites of Al2O3/LaPO4 were prepared using tape casting technique. Alumina slurry with acrylic latex binder was cast first on a polyester film, dried and then coated by LaPO4 interlayer cast on it. The coated green tapes were dried, stacked and laminated. After the removal of the binder, the green body was hot pressed in argon atmosphere at 1280 °C. A series of experiments were designed and conducted to investigate the influence of geometrical factors on mechanical properties of multilayer composites. Work-of-fracture of layered composites as high as 1100 J/m2 has been found.

Concise encyclopedia of composite materials

Abstract: Alphabetical listing of articles Aircraft Materials, R. Boyer Alternative Techniques for Manufacturing Composite Aerospace Designs, Cost of, Williamson Asbestos, F. Habashi Automotive Body Materials, A. M. Sherman, A. R. Krause, P. A. Friedman, D. A. Steenkamer and D. Q. Huston Automotive Chassis/Suspension Materials, G. Cole Bearing Materials: Plain Bearings, G.C. Pratt Biological Materials: Synthesis, Structure, and Properties, P. Calvert Biomimetic Materials: Properties and Processing, P. Calvert Bitumens: Modified, P. Nayler Block Copolymers as Precursors to Porous Materials, T.P. Russell and J.L. Hecrick Block Copolymers as Templates for Functional Materials, R.E. Cohen Bone and Natural Composites: Properties, J. D. Currey Bone Augmentation and Repair, E.L. Hedberg and A.G. Mikos Buildings: Plastics and Composites, F. J. Heger and P. A. Sharff Carbon Aerogels, H. Tamon Carbon Blacks, E.B. Senpl amd R.L. Taylor Carbon Fibers, L. M. Manocha Carbon Nanofibers, R. T. K. Baker Carbon Nanotubes, S. Subramoney Carbon-Carbon Composites, W. J. Lackey Ceramic Fibers from Polymer Precursors, K. Okamura Ceramic Matrix Composites with Roughly Equiaxed Reinforcements: Microstructure and Mechanical Behavior, G. Fantozzi and J. Chevalier Ceramic Matrix Composites: Applications, K. M. Prewo and W. K. Tredway Ceramic Matrix Composites: Matrices and Processing, R. R. Naslain Ceramic Nanocomposites with Organic Phases, Optics of, A. Biswas, C. S. Friend and P. N. Prasad Ceramic-modified High-temperature Polymers, Z. Ahmad Ceramics and Glasses, Sol-Gel Synthesis of, P.P. Thule and T.E. Wood Ceramics: Whisker Toughening, P.F. Becher Cermets and Hardmetals, D. Mari Clay-based Polymer Nanocomposites, A. Usuki Composite Dental Materials: Wear, K. Goovaerts, P. Lambrechts, J. De Munck, L. Bergmans and B. Van Meerbeek Composite Materials, Microstructural Design of, M. F. Ashby Composite Materials: Environmental Effects, A. R. Bunsell Composite Materials: Overview, A. Kelly and A. Mortensen Composites for Biomedical Applications, E. Wintermantel, J. Mayer and T. N. Goehring Composites for Sensors and Actuators, C. Boller Composites, Joining of, F. L. Matthews Composites, Microstructure of: Quantitative Description, J.-L. Chermant and M. Coster Composites, Physical Properties of, P. J. Withers Composites: Interfaces, T. W. Clyne Concrete as a Building Materials, C. K. Y. Leung Concrete: Failure Mechanics, J. G. M. van Mier Construction: Cellular Materials, F.-J. Ulm Construction Materials: Lightweight Aggregates, A.L. Bush Continuous Parallel Fiber Composites: Deformation and Strength, L. N. McCartney and W. R. Broughton Continuous Parallel Fiber Composites: Fracture, B. S. Majumdar and D. Hunston Conventional and Super Abrasive MaterialsR. Komanduri and S. Iyengar Creep and Creep-fatigue of Metal-Matrix Composites, G. F. Eggeler Creep of Bituminous Aggregates, S.F. Brown Creep of Concrete, Z. P. Bazant Creep of Particle Reinforced Materials, J. Rosler CVD Monofilaments, A. R. Bunsell Designing with Composites, S. M. Spearing and P. A. Lagace Elastic Behavior of Cellular Solids, A. M. Kraynik and M. K. Neilsen Elastic Behavior of Composites, A. Cervenka Elastic Structures in Design, H. R. Shercliff and M. F. Ashby Elasticity in Wood and Concrete: Hygromechanical Effects, J. Brauns and K. Rocens Elastomers, Ceramic-modified, J. H. Mark Elastomers, Reinforcement of, A. I. Medalia Electronic Packaging: Conductive Adhesives, A. M. Lyons Electronic Packaging: Elastomer Conductive Polymers, L. S. Buchoff Electronic Packaging: Heat Sink Materials, C. Zweben Fatigue of Particle Reinforced Materials, N. Chawla and J. E. Allison Fiber Metal Laminates, Fatigue of, A. Vlot and R. C. Alderliesten Fiber Strength, D. M. Wilson Fiberglass, N.M. Cameron and C.F. Rapp Fibers: Superabsorbant, T.F. Cooke Fibrous Reinforcements for Composites: Overview, K. K. Chawla Foams, Microrheology of, A.M. Kraynik and D.A. Reinelt Functionally Graded Materials, A. Neubrand Glass Fibers, K. K. Chawla Hard Tissues, Mechanical Properties of, J.Y. Rho High Performance Fibers, A. R. Bunsell Inorganic and Inorganic-Organic Aerogels, U. Schubert and N. Husing Inorganic Nanotube Materials, R. Tenne Laminates: Physical and Mechanical Behavior, L. N. McCartney Liquid Crystalline Polymers, Dispersed, E. Terentjev Lumber: Laminated Veneer, H. Sasaki Magnets: Bonded Permanent Magnets, K. H. J. Buschow Materials Selection and Mechanical Design, E. Maine and M. F. Ashby Mechanical Alloying, A. R. Jones Mechanical Testing Methods of Fibers and Composites, U. Ramamurty Membrane-based Polymer-Ceramic Nanocomposites Z. Pu Mesoporous Molecular Sieves, Th. Maschmeyer, M.E. Raimondi and J.M. Seddon Metal Matrix Composites with Roughly Equiaxed Reinforcements: Microstructure and Mechanical Behavior, D. Lloyd Metal Matrix Composites, Recycling of, H. P. Degischer Metal Matrix Composites: Applications, W. H. Hunt Metal Matrix Composites: Matrices and Processing, T. W. Clyne and F. R. Jones Metallic Filaments, H. U. Kunzi Mineral-filled Polymers, B. Pukanszky Modeling: Scaling Analysis (should change the title), C. L. Tucker III Nanoscale Ceramic Composites, G.S. Thompson and M.P. Harmer Natural Cellulose Fibers and Membranes: Biosynthesis, B. Ranby Natural Cellulose Fibers: Properties, L. Lohler Natural Protein Fibers, C. Viney Optical Properties of Functional Hybrid Organic-Inorganic Nanocomposites, C. Sanchez and B. Lebeau Organic Aerogels, R. Pekala and J. Fricke Organic Analogues to Zeolites and Mesoporous Sieves, D.L. Gin and S.A. Miller Organic-Inorganic Composite Crystals, D.B. Mitzi Paper Products: Classification, J.F. Waterhouse Paper: Creep, D.W. Coffin and C. Fellers Paper: Effects of Moisture and Temperature, D.F. Caulfield and A.H. Nissan Paper: Pulping and Bleaching, H.L. Hintz Paper: Strength and Stiffness, C. Fellers and D.W. Coffin Paper: Structure, R. Perkins Papermaking, N.A. Poirier, I.I. Pikulik and R. Gooding PES and PEEK, K. J. L. Burg and S. W. Shalaby Plastic Deformation of Cellular Materials, M. F. Ashby Polymer Composites, Friction and Wear of, K. Friedrich and R. Reinicke Polymer Fiber Processing: High-performance Fibers, T. Kitagawa Polymer Fibers: Formation and Structure, T. Kikutani Polymer Matrix Composites with Roughly Equiaxed Reinforcements: Microstructure and Mechanical Behavior, H. H. Kausch and Ph. Beguelin Polymer Matrix Composites, Recycling of, P. Sunderland Polymer Matrix Composites: Applications, A. Beukers Polymer Matrix Composites: Matrices and Processing, C. J. G. Plummer, P.-E. Bourban and J.-A. E. Manson Polymer Melt Mixing: Agglomerate Dispersion, I. Manas-Zloczower Polymer Modified Wood, M.H. Schneider Polymer Nanocomposites with Metal Dispersions, A. B. R. Mayer Polymer Transcrystallinity in Composites, R. J. Young and M. Heppenstall-Butler Polymer-based Nanocomposites by Sol-Gel Routes, Applications of, H. Schmidt and M. Stadtwald-Klenke Polymer-Ceramic Nanocomposites: Catalysts, S. Wang Polymer-Ceramic Nanocomposites: Ceramic Phases, P. Xu Polymer-Ceramic Nanocomposites: Control of Shrinkage, M. W. Ellsworth Polymer-Ceramic Nanocomposites: Interfacial Bonding Agents, C. Kumudinie Polymer-Ceramic Nanocomposites: Polymer Overview, L. C. Klein and A. B. Wojcik Polymer-modified Ceramics, Y. Wei Polymer-Nonsilica Ceramic Nanocomposites, J. K. Premachandra Polymer-Silica Nanocomposites, J. Wen Polymers in Constrained Ceramic Environments, H. L. Frisch and L. Huang Porous Ceramic Processing, D. J. Green Porous Silica Xerogel, C. Jin Portland Cements, J. F. Young Powders, Solution Synthesis of, R. E. Riman Processing Flexible Polymers to High Performance Fibers, P. J. Lemstra and S. Rastogi Processing Rigid Polymers to High Performance Fibers, S. J. Picken, H. Boerstoel and M. G. Northolt Pulp and Paper: Nonfibrous Components, D.P. Rawski Radiation Effects in Carbon-Carbon Composites, T. D. Burchell Reaction Forming, K. H. Sandhage and N. Claussen Reactive Ceramic Nanocomposites with Organic and Bio-organic Phases, D. Avnir, J. Blum and O. Lev Reinforced Concrete, A. E. Naaman Roofing Materials, C.G. Cash Rubber Tires, M. B. Rodgers Sporting Materials: Ski Equipment, H. Casey Spun (Slurry and Sol-Gel) Ceramic Fibers, D. M. Wilson Superconducting Wires and Cables: Materials and Processing, P. J. Lee Supported Catalysts, J.E. Bailie, G.J. Hutcings and S. OLeary Textile Fibers: A Comparative Overview, J. W. S. Hearle Textile Fibers: Mechanical Properties, W. Oppermann Thermally Contracting Materials, A. W. Sleight Whiskers, J. Katz Wood Composites: Mineral-bonded, A. A. Moslemi Wood Products: Decay during use, W.W. Wilcox Wood Products: Weathering, P.D. Evans Wood, Constituents of, A.G. McDonald Wood: Creep and Creep Rupture, E. Karacabeyli Wood: Macroscopic Anatomy, E. Wheeler Wood: Moisture Content, Hygroscopicity, and Sorption, I. Hartley Wood: Nonstructural Panel Processes, F. A. Kamke Wood: Nonstructural Panels, T. Adcock and M. P. Wolcott Wood: Strength and Stiffness, D.W: Green Wood: Structural Panel Processes, A. W. Boehner Wood: Structural Panels, M. R. O'Halloran Wood: Thermal Properties, T.E. Conners Wood: Ultrastructure, T.E. Conners Wood-Plastic Composites, M. P. Wolcott Xerogels, G.W. Scherrer Zeolites, A. Dyer

Oxide-based ceramic matrix composites

Abstract: An oxide-based ceramic matrix composite and a method of making oxide-based ceramic composite are provided. The oxide-based ceramic matrix composite comprises a ceramic fiber and a mullite-alumina impregnating the ceramic fiber, wherein the mullite-alumina ceramic matrix comprises 10-70 wt% mullite-alumina mixture.

Poly(borosiloxanes) as precursors for carbon fiber ceramic matrix composites

Abstract: Ceramic matrix composites (CMCs), constituted of a silicon boron oxycarbide (SiBCO) matrix and unidirectional carbon fiber rods as a reinforcement phase, were prepared by pyrolysis of carbon fiber rods wrapped in polysiloxane (PS) or poly(borosiloxane) (PBS) matrices. The preparation of the polymeric precursors involved hydrolysis/condensation reactions of alkoxysilanes in the presence and absence of boric acid, with B/Si atomic ratios of 0.2 and 0.5. Infrared spectra of PBS showed evidence of Si-O-B bonds at 880 cm-1, due to the incorporation of the crosslinker trigonal units of BO3 in the polymeric network. X ray diffraction analyses exhibited an amorphous character of the resulting polymer-derived ceramics obtained by pyrolysis up to 1000 °C under inert atmosphere. The C/SiBCO composites showed better thermal stability than the C/SiOC materials. In addition, good adhesion between the carbon fiber and the ceramic phase was observed by SEM microscopy

Effective fracture toughness in Al2O3–Al2O3/ZrO2 laminates

Abstract: During the processing of laminar ceramics, biaxial residual stresses can arise due to the thermal mismatch between different layers. For ceramic multilayers, the beneficial consequences of compressive stresses at the surface are well known: increase in strength, apparent toughness and reliability. Nevertheless, the resulting tensile stresses may induce a negative influence in the effective fracture toughness if the tensile stresses are high. The weight function technique is used to assess the stress intensity factor corresponding to the residual stresses field. The influence of geometrical parameters such as thickness, number of layers and tension/compression thickness ratio is analyzed. For different multilayers (Al 2 O 3 − x Al 2 O 3 /(1 − x )ZrO 2 ), effective R -curves are presented. The existence of an optimal architecture that maximizes the toughening is exposed as well as two tendencies on the apparent R -curve that define different fracture patterns: brittle failure or layer-by-layer fracture.

Electromagnetic properties of silicon carbide foams and their composites with silicon dioxide as matrix in X-band

Abstract: Electromagnetic wave absorbing properties of SiC-foams and their composites with SiO2 as matrix are presented, including theory, numerical analysis, and results/discussion. The reflection coefficients of various SiC-foams and their composites with various dielectric parameters are calculated by numerical simulation. When SiC conductivities are in the range of 2-3 S m(-1) in the case of SiC-foams, or 2-5 S m(-1) in the case of composites, the minimum reflection coefficients can be obtained in the range of X-band of 8.2-12.4 GHz. These materials are light weight, heat-resistant, and good impedance match with the free space, and therefore, they are a good candidate as a wide-range frequency absorbent medium. (c) 2006 Published by Elsevier Ltd.

Alumina/Zirconia Micro/Nanocomposites: A New Material for Biomedical Applications With Superior Sliding Wear Resistance

Abstract: In the present investigation, the sliding wear behavior is described for Al2O3/ZrO2 micro/nanocomposites and monolithic alumina of similar grain size under defined conditions of a constant sliding speed and different loads (20–150 N) Nano ZrO2 particles (17 vol%) were observed uniformly distributing throughout the composites, and most of them were located within the matrix alumina grains The wear rate of the alumina and the micro/nanocomposites increased as the contact load increased and a clear transition in friction and wear behavior was observed in both materials However, the nanocomposite wear resistance at low contact loads was one order of magnitude higher than that of the alumina In the severe regime, no difference was observed among the materials The low wear rate (10−7 mm3·(N·m)−1) along with low pullout indicates higher wear resistance of micro/nanocomposites in the mild regime compared with monolithic alumina Based on the morphological observation of worn surfaces by scanning electron microscope and on residual stress analysis performed by neutron diffraction, some wear mechanisms of Al2O3–ZrO2 micro/nanocomposites are proposed The high wear resistance of the nanocomposites is discussed in terms of fracture resistance properties and residual stress Improvements in mechanical and tribological properties of these composites make them promising candidates for biomedical applications

In-Plane Cracking Behavior and Ultimate Strength for 2D Woven and Braided Melt-Infiltrated SiC/SiC Composites Tensile Loaded in Off-Axis Fiber Directions

Abstract: The tensile mechanical properties of ceramic matrix composites (CMC) in directions off the primary axes of the reinforcing fibers are important for architectural design of CMC components that are subjected to multi-axial stress states In this study, 2D-woven melt-infiltrated (MI) SiC/SiC composite panels with balanced fiber content in the 0 degree and 90 degree directions were tensile loaded in-plane in the 0 degree direction and at 45 degree to this direction In addition, a 2D triaxially-braided MI composite panel with balanced fiber content in the plus or minus 67 degree bias directions and reduced fiber content in the axial direction was tensile loaded perpendicular to the axial direction tows (ie, 23 degrees from the bias fibers) Stress-strain behavior, acoustic emission, and optical microscopy were used to quantify stress-dependent matrix cracking and ultimate strength in the panels It was observed that both off-axis loaded panels displayed higher composite onset stresses for through-thickness matrix cracking than the 2D-woven 0/90 panels loaded in the primary 0 degree direction These improvements for off-axis cracking strength can in part be attributed to higher effective fiber fractions in the loading direction, which in turn reduces internal stresses on critical matrix flaws for a given composite stress Also for the 0/90 panel loaded in the 45 degree direction, an improved distribution of matrix flaws existed due to the absence of fiber tows perpendicular to the loading direction In addition, for the +67/0/-67 braided panel, the axial tows perpendicular to the loading direction were not only low in volume fraction, but were also were well separated from one another Both off-axis oriented panels also showed relatively good ultimate tensile strength when compared to other off-axis oriented composites in the literature, both on an absolute strength basis as well as when normalized by the average fiber strength within the composites Initial implications are discussed for constituent and architecture design to improve the directional cracking of SiC/SiC CMC components with MI matrices

Ceramic matrix composites with gradient concentration of metal particles

Abstract: The design of ceramic–metal composites with a gradient concentration of the metal particles fabricated by the slip casting method is presented. The gradient concentration of the metal particles was achieved through their sedimentation under the action of the gravitational force and a magnetic field. The paper describes the method of calculating the distance between the ceramic particles and indicates the correlation between this distance and the size of the metal particles. Preliminary experimental results of fabricated Al2O3–Fe composites confirmed the calculations. The metal particles, whose density is higher than that of ceramic particles, can undergo gravity-induced sedimentation only when the distance between the ceramic particles is greater than the diameter of these metal particles. With a slip casting containing 50 vol.% of solid phase, no concentration gradient of metal particles occurred. The Fe gradient concentration was achieved when the sedimentation was aided by a magnetic field.

Ceramic matrix composites with a gradient concentration of metal particles

Abstract: Abstract The design of ceramic–metal composites with a gradient concentration of the metal particles fabricated by the slip casting method is presented. The gradient concentration of the metal particles was achieved through their sedimentation under the action of the gravitational force and a magnetic field. The paper describes the method of calculating the distance between the ceramic particles and indicates the correlation between this distance and the size of the metal particles. Preliminary experimental results of fabricated Al2O3–Fe composites confirmed the calculations. The metal particles, whose density is higher than that of ceramic particles, can undergo gravity-induced sedimentation only when the distance between the ceramic particles is greater than the diameter of these metal particles. With a slip casting containing 50 vol.% of solid phase, no concentration gradient of metal particles occurred. The Fe gradient concentration was achieved when the sedimentation was aided by a magnetic field.

Yttrium silicate coating system for oxidation protection of C/C–Si–SiC composites: Electrophoretic deposition and oxygen self-diffusion measurements

Abstract: Yttrium silicate (YSI) coatings are promising complements to SiC coatings for protecting C/C–Si–SiC composites against oxidation owing to the pronounced chemical and mechanical properties of this material (low Young's modulus, low thermal expansion coefficient, low evaporation rate and oxygen permeability, good erosion resistance) Under control of deposition voltage and duration, yttrium silicate coatings of various thicknesses were electrophoretically deposited from powder suspensions The protectiveness of these coatings was tested by means of thermogravimetric analysis in air Diffusion data for oxygen in yttrium silicate needed to correlate the experimentally obtained oxidation rates in a phenomenological model were obtained by the IEDP (isotope exchange depth profiling) method from tracer diffusion measurements in single crystalline yttrium silicate and compared to diffusion data in mullite

Polysilazane-derived antibacterial silver-ceramic nanocomposites

Abstract: Functional ceramic composites consisting of a dispersion of silver nanoparticles in a silicon (carbon)nitride matrix ( nc -Ag/Si(C)N) were prepared via the polymer–ceramic route. Mixtures of 3 wt% as-synthesized Ag nanoparticles with a commercial polysilazane were pyrolysed under flowing nitrogen and/or ammonia. Bulk samples as well as coatings were investigated. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal analysis (TGA, DTA), absorption spectroscopy (UV–vis) and infra red (IR) spectroscopy were used to characterize the products. The results indicate that the silver nanoparticles do not influence the cross-linking and pyroylsis process of the polysilazane precursor. At temperatures in the range of 800–1000 °C (H)Si(C)N matrices are obtained, which contain silver particles with an average size of 5–7 nm. Antibacterial tests on the pyrolysed material revealed strong activity against Escherichia coli and Staphylococcus aureus , suggesting the composites to be promising candidates for applications in fields such as the biomedical or food industries.

Environmental Effects on Engineered Materials

Abstract: Metallic alloys: ferrous alloys (ferritic and martensitic) austenitic stainless steels nickel-based alloys for resistance to aqueous corrosion nickel-based alloys for resistance to high-temperature corrosion corrosion of copper and its alloys reactive and refractory alloys aluminium alloys magnesium alloys. Intermetallic alloys: environmental embrittlement of nickel-based and iron-based intermetallics. Ceramics: nonoxide ceramics oxide ceramics. Composites: metal matrix composites ceramic matrix composites issues in predicting long-term environmental degradation of fibre-reinforced plastics. Metallic glasses: amorphous and nanocrystalline alloys.

Sinterability, microstructures and electrical properties of Ni/Gd-doped ceria cermets used as anode materials for SOFCs

Abstract: The influence of Ni content in Ni–CGO cermets on their electrical conductivity was investigated in order to create the most suitable microstructure. Ni–CGO (50/50, 45/55 and 40/60 wt%) powder mixtures were prepared by the polymeric organic complex solution method using ethyleneglycol as a polymerized soluble alcohol in water. By heat treatment a composite of ultrafine nickel oxide homogeneously dispersed in the CGO ceramic matrix was attained. After sintering of NiO–CGO composites in air at 1350 °C for several times and reducing treatment in N 2 90%–H 2 10% atmosphere, the microstructures showed a uniform distribution of porous metallic Ni particles surrounded by microporous spaces with total porosity (closed and opened) of ≈20–25%. The electrical properties of Ni–CGO cermets sintered at 1350 °C for 2 h were studied using impedance spectroscopy in the temperature range from 500 to about 700 °C in argon atmosphere. The Ni–CGO cermets showed metallic behaviour over all the range at temperatures studied, indicating a uniform and fine-grained microstructure in which the Ni–Ni particle contacts were predominant.

Wavy CMC Wall Hybrid Ceramic Apparatus

Abstract: A ceramic hybrid structure (207, 502, 602, 608) that includes a wavy ceramic matrix composite (CMC) wall (214, 532, 603, 609) bonded with a ceramic insulating layer (230, 538, 604, 610) having a distal surface (242) that may define a hot gas passage (250, 550, 650) or otherwise be in proximity to a source of elevated temperature. In various embodiments, the waves (216, 537, 637) of the CMC wall (214, 532, 603, 609) may conform to the following parameters: a thickness (222) between 1 and 10 millimeters; an amplitude (224) between one and 2.5 times the thickness; and a period (226) between one and 20 times the amplitude. The uninsulated backside surface (218) of the CMC wall (214) provides a desired stiffness and strength and enhanced cooling surface area. In various embodiments the amplitude (224), excluding the thickness (222), may be at least 2 mm.