Ceramic-based Composites Research Articles

Zirconia-MWCNT nanocomposites for biomedical applications obtained by colloidal processing

Zirconia ceramics are widely used as femoral heads, but case studies show that delayed failure can occur in vivo due to crack propagation. The addition of carbon nanotubes (CNT) is aimed to avoid the slow crack propagation and to enhance the toughness of the ceramic material used for prostheses. However, to really enhance the mechanical properties of the material it is necessary to achieve a uniform distribution of the CNT in the zirconia matrix. Colloidal processing has demonstrated to be suitable for obtaining ceramic-based composites with homogeneous distribution of the phases and high green density. This work compares the colloidal behavior of the as-received multi wall carbon nanotubes (ar-MWCNT) and the partially coated MWCNT (pc-MWCNT) when immersed in a nanozirconia matrix. With pc-MWCNT an improvement in the dispersion is proved. Moreover, the sintered samples that contain pc-MWCNT show higher density, lower grain size, improved toughness and enhanced hardness under the same sintering cycle when compared to the samples with ar-MWCNT.

Beyond hardness: Ceramics and ceramic-based composites for protection

Because of their lightweight and high hardness, ceramics have been successfully used in protection technologies for over 40 years. The high hardness of a ceramic enables it to break, fragment, and deform impacting projectiles. This paper deals with a number of issues connected to the application of ceramics to ballistic protection, including ceramic hardness, inelastic deformation mechanisms, basic ballistic phenomenology and experimentation, ceramic damage due to ballistic impact, performance/failure maps based upon specific damage/failure mechanisms, and what possible future types of ceramics the suppression of these damage/failure mechanisms guide us to.

Tough, Bio-Inspired Hybrid Materials

The notion of mimicking natural structures in the synthesis of new structural materials has generated enormous interest but has yielded few practical advances. Natural composites achieve strength and toughness through complex hierarchical designs that are extremely difficult to replicate synthetically. We emulate nature's toughening mechanisms by combining two ordinary compounds, aluminum oxide and polymethyl methacrylate, into ice-templated structures whose toughness can be more than 300 times (in energy terms) that of their constituents. The final product is a bulk hybrid ceramic-based material whose high yield strength and fracture toughness [ approximately 200 megapascals (MPa) and approximately 30 MPa.m(1/2)] represent specific properties comparable to those of aluminum alloys. These model materials can be used to identify the key microstructural features that should guide the synthesis of bio-inspired ceramic-based composites with unique strength and toughness.

Composites reinforced with single crystalline oxide fibres: experiments and modelling

Metal- and ceramic-based composites reinforced with single crystalline oxide fibres promise an essential advance in developing heat-resistant composites. However, to reach a goal of making composites, which would be high creep resistant at very high temperatures and sufficiently damage tolerant at room temperature, a number of scientific and technological problems must be solved. The paper focuses on a particular feature of metal- and oxide-matrix composites, which is an interaction between fibre and matrix yielding considerable changes in microstructure and effective properties of both constituents. A special attention is drawn to a possibility to organize a synergetic fibre/matrix interaction to obtain composites with really new properties.

Microstructure and thermal characteristic of Si-coated multi-walled carbon nanotubes

The carbon nanotube (CNT) is a promising reinforcement material for manufacturingmetal-or ceramic-based composites. However, CNTs are prone to interact with the matrixin a reactive atmosphere that often alters the structure and properties of CNTs anddepresses their reinforcing effect. To overcome this problem, a protective silicon layerhas been deposited on multi-walled carbon nanotubes (MWNTs) using cycledvacuum-feeding chemical vapour deposition by the in situ decomposition of gaseousSiH4. The silicon coating is well covered and continuous with a cubic-phase structure. Iteffectively improves the thermal stability of MWNTs by acting as a protective film,which inhibits and delays the onset of oxidation. Thermogravimetric analysis(TGA) reveals that the oxidation of Si-coated MWNTs occurs at a temperature of676.3 °C, whichis 105.1 °C higher than that of uncoated MWNTs, and the weight loss decreases with the increasingthickness of silicon coating.

Development and use of an apparatus for tribological evaluation of ceramic-based brake materials

Automotive braking systems normally employ brake discs made of steel or grey cast iron, which are then paired with composite organic brake pads. These types of materials are suitable for use in braking systems with moderate loads, but car manufacturers are tending to design increasing numbers of prestige and sports-class vehicles that need braking systems with more braking power. As a result, new materials are being introduced into braking systems, for example, carbon–ceramic C/C SiC composites. However, much higher temperatures are generated at these ceramic surfaces, which imply some new requirements for the contact materials and the testing equipment. In this paper, we present a new tester dedicated for evaluating the tribological performance of ceramic-based composites for brake applications that uses reduced-scale samples with conformal contacts. The size of the samples was determined on the basis of the vehicle's speed (0–300 km/h), the contact pressure (0.1–10 MPa), the temperature (20–900 °C) and the geometrical proportions of full-scale braking systems. Special care was taken over the testing-head design in order to ensure control and measurement of the high temperatures that are generated at the contact. The simplicity and small size of the samples made it relatively easy to perform the various surface analyses. The theoretical background, the mechanical design and the controls of the testing device are presented. The functionality and reliability of the new device and the testing procedures were verified by using two brake-material combinations: conventional grey cast iron against a metal–matrix composite and a carbon–ceramic composite against a metal–matrix composite. The results confirmed our assumptions about the very high temperatures that are generated at the ceramic contacts and the necessity for well-controlled contact conditions. In addition, these first results suggest there are some beneficial frictional properties with a new material combination using in-house-developed MMC pads and C/C SiC discs.

Microstructure and erosive wear in ceramic-based composites

The overall objective of the study is to improve our current understanding regarding to the influence of microstructural properties on wear behavior of ceramic–metal composites. In this study the effect of microstructure variables on wear of multiphase materials is analyzed with reference to WC-, TiC-, and Cr 3C 2-based ceramic–metal composites (so called cermets). These variables are not limited to matrix grain size and porosity. The grain boundary microstructure and composition plays an important role in wears of heterogeneous materials. Further, the stresses generated by boundary crystallization may determine the tribological behavior of composites. Thermomechanical effects on erosive wear are discussed. Microstructure of each material was characterized with scanning electron microscopy (SEM). The ways in which composition and microstructure influence the erosive wear are examined. Results indicate that microstructural parameters play an important role in determining wear resistance of composite materials whereas the measured bulk properties seem to be of minor importance.

Shock–induced brittle failure of boron carbide

The mechanism for the failure of brittle materials during uniaxial compressive shockloading has been the subject of much discussion. In particular, the physical interpretation of the yield point, t...

Micromechanics of Stiffness Damage in Ceramic-Based Fiber-Reinforced Composites

The micromechanical analysis is performed to elucidate the stiffness reduction damage in the ceramic/ceramic composite whose matrix rupture strain is smaller than that of fibers. It is assumed that damage mechanism in the composite consists mainly of crack bridging fiber and interfacial sliding between the matrix and fibers. Energy release rate for a matrix crack and energy dissipation by the interfacial sliding was formulated by means of the inclusion modeling in micromechanics. Macroscopic stiffness at the given applied stress was derived in terms of the current lengths of matrix cracks. Finally, applicability of a parameter of damage accumulation in the material and its effect on macroscopic stiffness were discussed by the use of macroscopic stress-strain curves.

125 セラミック基複合材料の損傷域拡大高靭化機構(OS 複合材料CMC及びMMC)

125 セラミック基複合材料の損傷域拡大高靭化機構(OS 複合材料CMC及びMMC)

Micromechanical Analysis of the Effect of Temperature on Toughness of Ceramic-Based Fiber-Reinforced Composites.

Micromechanical Analysis of the Effect of Temperature on Toughness of Ceramic-Based Fiber-Reinforced Composites.

Tribological Characteristics of Si3N4-based Self-Lubricating Materials

A new technique for fabrication of self-lubricating ceramic-based composites has been developed. Multi-channel ceramic matrices with a predetermined number, diameter, and distribution of channels are fabricated and then filled with a lubricant such as polytetrafluoroethylene or perfluoropolyether. Friction coefficients of lubricant-filled silicon nitride against 52100 steel were found to be 0.1 to 0.2, in contrast with pure silicon nitride for which values of 0.6 to 0.7 were found. This friction reduction is insensitive to applied load or to sliding speed. The controlled pattern of porosity allows these materials to have lubricant loading of 7.5 to 10 volume percent, instead of 20–25% typical of traditional self-lubricating materials. This configuration permits higher crushing resistance and stiffness in comparison with conventional self-lubricating antifriction materials. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Effect of Alcohol Solvent on Mixing of Fine Ceramic Powders and Some Properties of Ceramic-Based Composites.

Effect of alcohol solvent in mixing process on the microstructure and sintering behavior of ceramic-based composites was investigated in detail. The mixture of fine ceramic powders was prepared through the conventional ball-milling method with various alcohol media. The particle distributions of fine ceramic powders were strongly dependent on the kind of alcohol employed during ball-milling. Ceramic-based composites were fabricated by hot-pressing the mixture of fine ceramic powders. Their microstructures and some mechanical properties of the ceramic-based composites were evaluated. It was found that the viscosity of alcohol, surface tension and contact angle greatly affect the sinterability and some of the mechanical properties of ceramic-based composites.

Designing of textile preforms for ceramic matrix composites

Two and three dimensional fiber preforms produced by textile forming techniques have been used successfully for reinforcing ceramic-based composites. The focus of this paper is on the design of textile preforms for reinforcing ceramic matrix composites. The research work consisted of the following tasks: (1) identification of typical loading conditions on composite structural elements; (2) determination of the requirements on the orientation and volume content of fiber reinforcement; (3) identifying the fiber preforms suitable for each loading condition; (4) identifying the preforming technologies available for producing the preforms; (5) analysis and modeling of the thermo-mechanical behavior of the textile composites, using the concepts of micro- and macro-cells; and (6) characterization of textile composite performance.

A Study of Structure Formation and Failure of Short Fibre Composites with Metal and Ceramic Matrices

An experimental study of the fracture behaviour of metal- and ceramic-based composites containing randomly oriented short fibres, related to fabrication parameters of those composites produced by a powder metallurgy method, yields a suggestion to describe the failure of such composites with a multi-scale model. A most important feature of the failure behaviour is an occurrence of the maximum strength of a composite at rather low values of the fibre volume fraction.

Influence of substrate orientation on wetting kinetics in reactive metal/ceramic systems

The kinetic factors of the liquid–solid interface formation process are extremely useful in the design of composite preparation methods and the manufacture of comprehensive performance-controlled metal- or ceramic-based composites. Here, we review the available spreading dynamic models, focusing on wetting at high temperatures. There is yet to be developed a general spreading dynamic model with complete physical meaning that can accurately describe complicated surface–interface kinetic processes at high temperatures. In this work, we highlight common analysis errors in the description of the spreading dynamics for metal–ceramic and metal–metal systems. By unifying the expressions of the spreading dynamic models as the function f(v, θd) and fitting the experimental data reported in the literature, we discovered that the molecular-kinetic model commonly used to describe adsorption-controlled spreading at room temperature and reaction-limited spreading model used at high temperature have a certain range of overlap. When the condition σlv(cosθe–cosθd) < <2nkBT is satisfied, these models are consistent in terms of mathematical functional expressions. As a result, distinguishing between them when the spreading behavior includes both adsorption and reaction is challenging.

New Nanocomposite Structural Ceramics

ABSTRACTThe new materials design was established for the structural ceramics to break through the present monolithic and composite ceramics. In this concept, the ceramic-based composites were divided into two groups: micro and nanocomposite. The microcomposite is the so-called composite in which the micro-sized particles, whiskers, platelets and fibers are dispersed at the grain boundaries of matrix grains. The nanocomposites, on the other hand, have three types of structures: intra and intergranular nanocomposites and nano/nano composite. The intra and intergranular nanocomposites were found to show the tremendous improvement of mechanical properties even at elevated temperatures compared with those of monolithic and microcomposite ceramics. The nano/nano composites gave the new functions such as machinability and superplasticity like metals. Our final goal for developing supertough and strong ceramics was achieved by hybridizing the intra and intergranular nanocomposites with the micro-meter sized fibers. This new concept was found to be also applicable for ceramic-metal composite systems.