Showing papers on "Ceramic matrix composite published in 2004"
TL;DR: SiC-based ceramic matrix composites, consisting of carbon or SiC fibers embedded in a SiC-matrix, are tough ceramics when the fiber/matrix bonding is properly optimized through the use of a thin interphase.
1,358 citations
TL;DR: In this paper, a highly ordered array of parallel multi-wall CNTs in an alumina matrix was fabricated and the damage was examined by scanning electron microscopy, and the quantitative indentation data and computational models were used to determine the multiwall axial Young's modulus as 200-570 GPa, depending on the nanotube geometry and quality.
442 citations
TL;DR: It is argued that the highly shear-deformable SWNTs or graphite heterogeneities in the Composites help redistribute the stress field under indentation, imparting the composites with contact-damage resistance.
Abstract: There has been growing interest in incorporating single-wall carbon nanotubes (SWNTs) as toughening agents in brittle ceramics. Here we have prepared dense Al2O3/SWNT composites using the spark-plasma sintering (SPS) method. Vickers (sharp) and Hertzian (blunt) indentation tests reveal that these composites are highly contact-damage resistant, as shown by the lack of crack formation. However, direct toughness measurements, using the single-edge V-notch beam method, show that these composites are as brittle as dense Al2O3 (having a toughness of 3.22 MPa m0.5). This type of unusual mechanical behaviour was also observed in SPS-processed, dense Al2O3/graphite composites. We argue that the highly shear-deformable SWNTs or graphite heterogeneities in the composites help redistribute the stress field under indentation, imparting the composites with contact-damage resistance. These composites may find use in engineering and biomedical applications where contact loading is important.
418 citations
TL;DR: In this article, the processing and properties of HfB2-20 vol%SiC ultra high temperature ceramics were examined and it was concluded that passive oxidation of SiC plays a role in determining the steady-state surface temperatures below 1700°C.
Abstract: The processing and properties of HfB2-20 vol%SiC ultra high temperature ceramics were examined. Dense billets were fabricated by hot-pressing raw powders in a graphite element furnace for 1 h at 2200°C. Specimens were then tested for hardness, mechanical strength, thermal properties and oxidation resistance in a simulated re-entry environment. Thermal conductivity of the current materials was found to be less than previous work had determined while the strength was greater. Oxidation testing of two flat-face models was conducted, at two conditions, for two 10-min durations each. It was concluded that passive oxidation of SiC plays a role in determining the steady-state surface temperatures below 1700°C. Above 1700°C, temperatures are controlled by the properties of a thick HfO2 layer and active oxidation of the SiC phase.
296 citations
TL;DR: In this paper, a review of crack deflecting coatings for fiber-reinforced ceramic composites is presented, and the implications on the design of coatings and of composite systems using alternative coatings are discussed.
Abstract: Fiber-reinforced ceramic composites achieve high toughness through distributed damage mechanisms. These mechanisms are dependent on matrix cracks deflecting into fiber/matrix interfacial debonding cracks. Oxidation resistance of the fiber coatings often used to enable crack deflection is an important limitation for long-term use in many applications. Research on alternative, mostly oxide, coatings for oxide and non-oxide composites is reviewed. Processing issues, such as fiber coatings and fiber strength degradation, are discussed. Mechanics work related to design of crack deflecting coatings is also reviewed, and implications on the design of coatings and of composite systems using alternative coatings are discussed. Potential topics for further research are identified.
261 citations
TL;DR: In this paper, the percolation of carbon nanotubes (CNT) in an electrical insulating ceramic is studied for the first time, and the results are discussed in relation with the characteristics of the CNT, their damaging during the hot-pressing at 1300 °C and the microstructure of the composites.
200 citations
TL;DR: In this paper, carbon nanotube reinforced ceramic composites were synthesized by using recently developed polymer-derived ceramics as matrices, and significant increases in mechanical and thermal properties were observed by adding only 6vol% nanotubes.
Abstract: Carbon nanotube reinforced ceramic composites were synthesized by using recently developed polymer-derived ceramics as matrices. Multi-wall carbon nanotubes, treated with a surfactant, were first dispersed in a liquid polymer precursor by sonication and mechanical stirring. The solution was then converted to fully dense ceramic composites with pressure-assist pyrolysis technique. Microstructural observation revealed that nanotubes were homogeneously dispersed throughout the ceramic matrix. Significant increases in mechanical and thermal properties were observed by adding only {approx}6vol% nanotubes. Strong nanotube pullout revealed by SEM observation suggested that the composites could possess high fracture toughness.
180 citations
TL;DR: In this article, a self-healing multilayered matrix is designed and used in a model composite, which combines B-doped pyrocarbon mechanical fuse layers and B 4 C and SiC layers forming B 2 O 3 -based fluid healing phases when exposed to an oxidizing atmosphere.
175 citations
TL;DR: In this paper, Zirconium diboride (ZrB2) based ultra-high temperature ceramics either unmodified or with SiC particulate additions of 10, 20, or 30 volume percent were prepared by conventional hot pressing.
Abstract: Zirconium diboride (ZrB2) based ultra-high temperature ceramics either unmodified or with SiC particulate additions of 10, 20, or 30 volume percent were prepared by conventional hot pressing. The ZrB2-SiC compositions had improved four-point bend strength compared to the ZrB2 prepared in our laboratory as well as other reported ZrB2 or ZrB2-SiC materials. Strength and toughness increased as the amount of SiC increased. Measured strengths ranged from ∼550 MPa for ZrB2 to over 1000 MPa for ZrB2-30% SiC. Likewise, toughness increased from 3.5 MPa to more than 5 MPa over the same composition range. The addition of SiC also improved oxidation resistance compared to pure ZrB2. Co-extrusion processing was used to produce ZrB2-based ultra-high temperature ceramics with a fibrous monolithic structure. Samples had dense ZrB2-30 vol% SiC cells approximately 100 μm in diameter surrounded by porous ZrB2 cell boundaries approximately 20 μm thick. ZrB2-based fibrous monoliths had four point bend strength of ∼450 MPa, about half of a conventional ZrB2-SiC ceramic with the cell composition. Preliminary analysis of fracture behavior found that ZrB2-based fibrous monoliths did not exhibit graceful failure because the difference in strength between the cell and cell boundary of the current materials was not sufficient.
166 citations
TL;DR: In this article, Yttrium silicate (Y 2 SiO 5 ) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon-fiber-reinforced SiC composites (C-SiC).
Abstract: Yttrium silicate (Y 2 SiO 5 ) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon-fiber-reinforced SiC composites (C-SiC). Thick (100 μm), dense Y 2 SiO 5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were studied by taking into account the simultaneous presence of oxide and non-oxide materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucibles and a SiC bed in an argon-flow furnace. Pure Y 2 SiO 5 coatings completely separated from the SiC substrates. A high percentage of Y 2 Si 2 O 7 was necessary to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated by isothermal and stepwise oxidation tests.
157 citations
TL;DR: In this article, a solution precursor plasma spray (SPPSP) process was used to obtain high spallation life for thermal barrier coatings. But, the failure of SPPS TBCs occurs within the ceramic top coat, near the ceramic/bond coat interface.
Abstract: The solution precursor plasma spray (SPPS) process offers the prospect of depositing highly durable thermal barrier coatings (TBCs) of low thermal conductivity. In this study, a Taguchi design of experiments was employed to optimize the SPPS process. The spallation life of SPPS TBCs on a MCrAlY bond coated Ni-base superalloy substrate deposited under the optimized processing conditions was demonstrated to be more than 2.5 times of that of a conventional plasma sprayed TBC with the same substrate and bond coat. The superior durability of SPPS TBCs is associated with their novel microstructures, which include: (i) a ceramic matrix containing micrometer and nanometer porosity, (ii) the presence of very fine splats (0.5 to 5-μm diameters), (iii) through-thickness cracks, and (iv) improved ceramic to bond coat adhesion. The failure of SPPS TBCs occurs within the ceramic top coat, near the ceramic/bond coat interface. Buckling spallation is the failure mode observed for all tested samples. It was also demonstrated that the SPPS process is capable of depositing thick (>2 mm) and durable TBCs.
TL;DR: In this article, a carbon fiber reinforced HfC matrix composite has been developed to promote graceful failure using a pyrolytic graphite interface between the reinforcement and the matrix.
Abstract: Hafnium carbide is proposed as a structural material for aerospace applications at ultra high temperatures. The chemical vapor deposition technique was used as a method to produce monolithic hafnium carbide (HfC) and tantalum carbide (TaC). The microstructure of HfC and TaC were studied using analytical techniques. The addition of tantalum carbide (TaC) in the HfC matrix was studied to improve the microstructure. The microstructure of HfC, TaC and co-deposited hafnium carbide-tantalum carbide (HfC/TaC) were comparable and consisted of large columnar grains. Two major problems associated with HfC, TaC, and HfC/TaC as a monolithic are lack of damage tolerance (toughness) and insufficient strength at very high temperatures. A carbon fiber reinforced HfC matrix composite has been developed to promote graceful failure using a pyrolytic graphite interface between the reinforcement and the matrix. The advantages of using carbon fiber reinforcement with a pyrolytic graphite interface are reflected in superior strain capability reaching up to 2%. The tensile strength of the composite was 26 MPa and needs further improvement. Heat treatment of the composite showed that HfC did not undergo any phase transformations and that the phases comprising composite were are thermochemically compatible.
TL;DR: In this paper, the authors studied the oxidation kinetics and mechanisms of SiC-matrix composites fabricated by chemical vapor infiltration, and of their constituents (C or SiC -fibers, C or BN interphases and SiC matrix) on the basis of an experimental approach and modelling.
Abstract: The oxidation kinetics and mechanisms of SiC-matrix composites fabricated by chemical vapor infiltration, and of their constituents (C or SiC-fibers, C or BN interphases and SiC matrix) are studied on the basis of an experimental approach and modelling. The oxidation of carbon fibers is rate-controlled by a combined diffusion/chemical reaction mechanism at low temperatures and its rate reduced by a 1600°C heat treatment. The oxidation rate of the pyrocarbon is similar to that of the fibers when they have been heat-treated. The oxidation kinetics of both the SiC-based fibers and matrix are parabolic and assumed to be rate-limited by the diffusion of gaseous species in the silica scale. A full kinetics law is given. The occurrence of water in the atmosphere increases the oxidation rate of the fibers and decreases the activation energy, water becoming the main oxidizing agent. The oxidation of the BN-interphase is complex and strongly anisotropic, its kinetics depending on composition, structure and texture. Finally, the oxidation of SiC-matrix composites, depicted for 1D-SiC/C/SiC and 2D-C/C/SiC composites, involves both diffusion of gaseous species in the composite porosity and heterogeneous oxidation reactions. Oxidation occurs through the thickness of the composites at low temperatures which consumes the carbon-based constituents. Conversely, it tends to be limited to near the composite surface at high temperatures, due to the formation of silica-based phases healing the material porosity and preventing the in-depth oxidation of the carbon-based constituents.
01 Jan 2004
TL;DR: Anisotropic, biomorphous SiOC/C-ceramic composites with different porosities and designed microstructure were manufactured from native beech and pine wood as mentioned in this paper.
Abstract: Anisotropic, biomorphous SiOC/C-ceramic composites with different porosities and designed microstructure were manufactured from native beech and pine wood. In a first step, biotemplate/polysiloxane composites were prepared by infiltration and reaction of the wood preforms with a Si–H functionalised preceramic polymer (polymethylhydrosiloxane—PMHS). Curing of the infiltrated PMHS was achieved by temperature treatment at 120 °C for 12 h. Subsequent pyrolysis of the biopolymer/polysiloxane hybrid materials in inert atmosphere at 800 °C yields a biomorphous SiOC/C-ceramic composite. FTIR, TGA and SEM analysis was applied to monitor structural changes and phase formation processes during thermal treatment. The esterification of the wood with maleic acid anhydride (MA) was used to alter the chemical properties of the wood cell wall and to introduce CC-double bonds for further reaction with PMHS. The PMHS-infiltration reduced the anisotropic shrinkage associated with the thermal decomposition of the biopolymers compared to the native wood. MA-modified, PMHS-infiltrated samples exhibit an improved ceramic yield after pyrolysis, which may be attributable to a facilitated penetration of the PMHS into the wood cell wall. Additionally, the influence of low-molecular weight wood compounds on the PMHS-infiltration as well as on the microstructural evolution was assessed by extraction techniques. Extraction of the low-molecular weight wood compounds yielded an additional porosity and finally void formation inside the SiOC-phase, which stabilizes the specimen during the pyrolysis and prevents the sample from cracking.
Patent•
13 Sep 2004
TL;DR: A sintered ceramic compact as discussed by the authors is characterized by a polycrystalline binding layer composed of ceramic fine particles and/or aggregates which are present among the ceramic coarse particles in such a manner as to link them and have an average particle diameter less than that of said coarse particles.
Abstract: A sintered ceramic compact, characterized in that it comprises ceramic coarse particles and a polycrystalline binding layer composed of ceramic fine particles and/or aggregates thereof which are present among the ceramic coarse particles in such a manner as to link them and have an average particle diameter less than that of said coarse particles; and a ceramic filter manufactured by using the sintered ceramic compact. The sintered ceramic compact or the ceramic filter can suppress the occurrence of a large crack due to the break of particles of silicon carbide in the case wherein a thermal stress is applied to the sintering compact in a re-treatment or the like, can suppress the deterioration of a catalyst carried on it in the case that it is re-treated repeatedly, and thus can be used stably for a long period of time.
TL;DR: In this article, an acrylic modified zircon loaded with alumina powders is used as organic photoactivated resin and allows the dispersion of a high volume fraction of Al2O3 powder (up to 50 vol%) while keeping viscosity at reasonable low values.
Abstract: Ceramic laser stereolithography is a manufacturing process suitable candidate for the production of complex shape technical ceramics. The green ceramic is produced layer by layer through laser polymerisation of UV curable ceramic suspensions. A number of critical issues deserve attention: high solid loading and low viscosity of the suspensions, high UV reactivity, prevention of interlayer delamination in the green and in the sintered body, good mechanical performance. In this work, ZrO2 reinforced Al2O3 components have been obtained from an acrylic modified zircon loaded with alumina powders. The zircon compound is effective as organic photoactivated resin and allows the dispersion of a high volume fraction of Al2O3 powder (up to 50 vol.%) while keeping viscosity at reasonable low values. The zircon compound also represents a liquid ceramic precursor that converts to oxide after burning out of the binder. Thanks to the good dispersion of the alumina powder in the zircon acrylate, a uniform dispersion of ZrO2 submicron particles is obtained after pyrolysis. These are located at the grain boundaries between alumina grains. Formation of both monoclinic and tetragonal ZrO2 occurs as evidenced by XRD. No delamination occurs in bending tests as evidenced by SEM fractography, satisfactory modulus and strength values were concurrently found.
TL;DR: The evolution of the microstructure during reactive Si melt infiltration was assessed by infiltration experiments at various times and investigated by X-ray diffraction as well as light scanning electron and transmission electron microscopy in combination with elemental analysis by energy-dispersive Xray spectrometry.
Abstract: Liquid Si infiltration (LSI) of beech wood-derived biocarbon (CB) templates at 1550°C yields biomorphous SiSiC ceramics with the morphology of the initial biological preform. The biomorphous SiSiC ceramic consists of solidified Si in the cell lumina, polycrystalline β-SiC and residual carbon islands located at the position of former wood cell walls. The evolution of the microstructure during reactive Si melt infiltration was assessed by infiltration experiments at various times and investigated by X-ray diffraction as well as light scanning electron and transmission electron microscopy in combination with elemental analysis by energy-dispersive X-ray spectrometry. Four different stages of the reactive infiltration process could be distinguished, starting with a heterogeneous nucleation of nano-grained SiC on the pore surfaces of the CB template by a Si vapor phase reaction below the Si melting temperature. After spontaneous Si melt infiltration, a stepwise reaction results in the simultaneous formation of a nano-grained SiC layer and a coarse-grained SiC phase on the inner pore surfaces. Further reaction proceeds slowly by diffusion of the reactants through the formed SiC layer and the microstructure evolution is dominated by dissolution and re-crystallization processes.
TL;DR: Si 3 N 4 /SiC composite ceramic specimens, made to JIS standard, were sintered and subjected to three-point bending as discussed by the authors, and they were made on the tensile side of each specimen.
Abstract: Si 3 N 4 /SiC composite ceramic specimens, made to JIS standard, were sintered and subjected to three-point bending. Semi-elliptical surface cracks of 50–400 μm in diameter were made on the tensile side of each specimen. Crack-healing behavior as a function of environment, temperature, time, and crack size, and oxidation behavior as a function of temperature and time were studied. The main conclusions are as follows: (1) Cracks healed completely in air, but did not heal in Ar gas, N 2 gas nor in a vacuum. (2) This Si 3 N 4 ceramic has the ability to heal a crack at temperature from 900 to 1400 °C completely. (3) The maximum surface crack size that can be healed completely was 200 μm in diameter. (4) The activation energies for crack-healing and oxidation were 150 and 131KJ/mol, respectively.
TL;DR: In this paper, a 3D titania matrix composite was fabricated by further infiltration of the porous fibrous preform with TiO2 by slurry dipping and subsequent pressureless sintering.
Abstract: Electrophoretic deposition (EPD) has been used to obtain TiO2 coatings on three dimensional (3-D) SiC fibre (Nicalon ®-type) and carbon fibre substrates. Colloidal suspensions of commercially available TiO2 nanoparticles in acetylaceton with addition of iodine were used. The EPD parameters, i.e., deposition time and voltage, were optimised for each fibre type. Strongly adhered TiO2 deposits with high particle packing density were obtained. Scanning electron microscopy observations revealed high penetration of the titania nanoparticles into the fibre preforms. The TiO2 deposits were sintered at 800°C for 1 h in order to produce relatively dense and uniform TiO2 coatings covering completely the SiC or carbon fibres. For the carbon fibre/TiO2 system, an effort was made to produce a 3-D titania matrix composite by further infiltration of the porous fibrous preform with TiO2 by slurry dipping and subsequent pressureless sintering. The 3-D carbon fibre reinforced TiO2 matrix composites fabricated contained residual porosity, indicating further infiltration and densification steps are required to produce dense composites of adequate structural integrity. For SiC fibre fabrics, oxidation tests in air established the effectiveness of the TiO2 coating as oxidation protective barrier at 1000°C. After 120 h the increase of weight due to oxidation of coated fibres was more than twice lower than that of the uncoated fibres. TiO2 coated SiC fibre preforms are attractive materials for manufacturing hot gas filters and as reinforcing elements for ceramic matrix composites.
15 Dec 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, it is shown that aluminium matrix composites containing 50% or more ceramic particles can be tough, strong and relatively ductile, despite the high ceramic loadings.
Abstract: It is commonly considered that, in ceramic particle reinforced metals, the volume fraction of ceramic should not exceed 30% if the composite is intended for structural applications: otherwise its toughness and ductility generally become unacceptably low. Particle reinforced metal matrix composites produced by infiltration provide a material with which this assumption can be tested. We first present a summary of recent results from our laboratory showing that aluminium matrix composites containing 50% or more ceramic particles can be tough, strong and relatively ductile, despite the high ceramic loadings. We then discuss toughening mechanisms that can explain the mechanical properties displayed by these composites, to highlight the importance of the particle strength distribution on the composite fracture toughness.
TL;DR: In this paper, the incorporation of up to 30% of spinel powder of median particle sizes 3, 11 and 22 μm into dense magnesia gives improved resistance to thermal shock as indicated both by the R − thermal shock resistance parameters calculated from measured mechanical properties, and by a standard quench test.
Abstract: The incorporation of up to 30% of spinel powder of median particle sizes 3, 11 and 22 μm into dense magnesia gives improved resistance to thermal shock as indicated both by the R ‴ thermal shock resistance parameters calculated from measured mechanical properties, and by a standard quench test. The loss of strength of the composite materials in the quench test matched satisfactorily that predicted by the R ‴ parameter. The maximum benefit from spinel additions was obtained with spinel of the largest particle size, at a loading of 20%. It is postulated that the pre-formed cracks in the composites, resulting from the thermal expansion mismatch between magnesia and spinel, inhibit the accumulation of strain energy during thermal shock.
TL;DR: In this article, a bio-template was used to produce morph-genetic TiC/C ceramics by infiltrating the carbon preform pyrolyzed from wood with tetrabutyl titanate, which was subsequently sintered at 1400 °C to produce the final ceramic structure.
Patent•
02 Dec 2004TL;DR: In this article, a turbine vane made of stacked ceramic matrix composite (CMC) laminates is described. But the design of the cooling features in the individual laminate can cooperate to form intricate three dimensional cooling systems in the vane.
Abstract: Embodiments of the invention relate to various cooling systems for a turbine vane made of stacked ceramic matrix composite (CMC) laminates. Each airfoil-shaped laminate has an in-plane direction and a through thickness direction substantially normal to the in-plane direction. The laminates have anisotropic strength characteristics in which the in-plane tensile strength is substantially greater than the through thickness tensile strength. Such a vane construction lends itself to the inclusion of various cooling features in individual laminates using conventional manufacturing and forming techniques. When assembled in a radial stack, the cooling features in the individual laminates can cooperate to form intricate three dimensional cooling systems in the vane.
TL;DR: In this article, reaction-bonded silicon carbide was used to fabricate the 250mm diameter circular mirror with 30mm thickness and 1.72-kg weight and the 120mm hexagonal mirror with 15mm thickness, and 0.23kg weight.
TL;DR: In this article, the effects of circular holes and sharp notches on the tensile strength of two Nicalon-reinforced ceramic composites have been investigated through measurements of the local strains in the regions of high stress concentration, coupled with finite element simulations of the test geometries, using a nonlinear constitutive law appropriate to ceramics.
Abstract: The effects of circular holes and sharp notches on the tensile strength of two Nicalon-reinforced ceramic composites have been investigated. The influence of inelastic straining on the redistribution of stress has been elucidated through measurements of the local strains in the regions of high stress concentration, coupled with finite element simulations of the test geometries, using a nonlinear constitutive law appropriate to ceramic composites. The scale dependence of strength has been inferred from tests performed on specimens of varying size. The utility of two failure models that incorporate both the inelastic straining and the scale dependence has been assessed: one based on the point stress failure criterion and the other on weakest-link fracture statistics. Both approaches provide a reasonably consistent description of the experimental measurements. Some of the implications and limitations associated with the failure models are discussed.
01 Jan 2004
TL;DR: In this paper, a textured monolithic alumina ceramics were synthesized by electrophoretic deposition (EPD) in strong magnetic field of 10 T. The results showed that the EPD is a promising ceramic processing technique for fabricating sophisticated ceramic composites.
Abstract: Textured monolithic alumina ceramics were synthesized by electrophoretic deposition (EPD) in strong magnetic field of 10 T. Single crystalline, granular α-alumina particles in aqueous suspensions were rotated due to their anisotropic diamagnetic susceptibility and then deposited on substrate. A multilayered alumina composite of oriented and randomly oriented layers was also synthesized by the alternate EPD of alumina suspensions which were placed in and out of a superconducting magnet. It was demonstrated that the EPD in a strong magnetic field is a promising ceramic processing technique for fabricating sophisticated ceramic composites.
TL;DR: In this article, the failure modes and degradation mechanisms of a carbon fiber-reinforced silicon carbide (C/SiC) composite at two temperatures, 600 and 1200 C, were identified.
Abstract: Stress-rupture tests were conducted in air, vacuum, and steam-containing environments to identify the failure modes and degradation mechanisms of a carbon fiber-reinforced silicon carbide (C/SiC) composite at two temperatures, 600 and 1200 C. Stress-rupture lives in air and steam containing environments (50 - 80% steam with argon) are similar for a composite stress of 69 MPa at 1200 C. Lives of specimens tested in a 20% steam/argon environment were about twice as long. For tests conducted at 600 C, composite life in 20% steam/argon was 20 times longer than life in air. Thermogravimetric analysis of the carbon fibers was conducted under similar conditions to the stress-rupture tests. The oxidation rate of the fibers in the various environments correlated with the composite stress-rupture lives. Examination of the failed specimens indicated that oxidation of the carbon fibers was the primary damage mode for specimens tested in air and steam environments at both temperatures.
TL;DR: In this article, a combined analytical and numerical model, using cohesive zone models for both matrix cracking and nanotube crack bridging and accounting for residual stresses, is developed to interpret the indentation results and evaluate the fracture toughness of the composite.
Abstract: The fracture toughness of highly-ordered multi-wall carbon-nanotube-reinforced alumina composites is calculated from experimental data on nanoindentation cracking. A combined analytical and numerical model, using cohesive zone models for both matrix cracking and nanotube crack bridging and accounting for residual stresses, is developed to interpret the indentation results and evaluate the fracture toughness of the composite. Results show that residual stress and nanotube bridging play important roles in the nanocomposite fracture. The contribution to toughness from the nanotube bridging for cracking transverse to the axis of the nanotubes is calculated to be similar to5 MPa-m(1/2). From the nanotube bridging law, the nanotube strength and interfacial frictional stress are also estimated and range from 15-25 GPa and 40-200 MPa, respectively. These preliminary results demonstrate that nanotube-reinforced ceramics can exhibit the interfacial debonding/sliding and nanotube bridging necessary to induce nanoscale toughening, and suggest the feasibility of engineering residual stresses, nanotube structure, and composite geometry to obtain high-toughness nanocomposites.
TL;DR: In this paper, a nanometer-scale polymer surface coating layer based on styrene-butadiene with varied concentrations, as environmental barrier interphase, was applied to the alkali-resistant glass fibers.
TL;DR: In this article, nanosized SiC reinforced TiC matrix composites were fabricated at 1600°C by spark plasma sintering (SPS) without any aids, and the phase distribution and microstructure of composites have been investigated by optical microscopy and scanning electron microscope.
Abstract: Different content of nanosized SiC reinforced TiC matrix composites were fabricated at 1600°C by spark plasma sintering (SPS) without any aids. It was found that the materials could be sintered in a relatively short time (12 min) and low sintering temperature (1600°C) to satisfactory relative density (99%). The phase distribution and microstructure of composites have been investigated by optical microscopy and scanning electron microscope. Fracture toughness and Vickers hardness at room temperature were also measured by indentation tests. The results showed that nanosized SiC particles addition could inhibit the coalescence of TiC grains and increase fracture toughness of composites due to the crack deflections.