Search

Tungsten powders were successfully sintered and simultaneously joined to a graphite disk using an interlayer of SiC ceramic powder, which contained Al 2 O 3 and Y 2 O 3 as sintering aids for the SiC. The tungsten/graphite joints were prepared at 30 MPa and temperatures ranging from 1700 °C to 2000 °C for 5 min using spark plasma sintering (SPS). The tensile strength of the joints prepared at 1700 °C reached 21 MPa. The suggested joining mechanism of the joints prepared below 1800 °C is as follows: both the sintered W metal layer and the SiC ceramic interlayer are chemically bonded together accompanying reaction phases of WC, W 2 C and W 5 Si 3 . A physical bond is achieved between the SiC interlayer and graphite when the SiC powder fills the open pores of the graphite and is sintered there. Although a similar joining mechanism is suggested when the joining temperature exceeds 1900 °C, the SiC interlayer disappears, and the broad reaction layer consisting of WC, W 2 C and trace W 5 Si 3 is formed. [ABSTRACT FROM AUTHOR]

Abstract: Unique porous SiC ceramics with a honeycomb structure were fabricated by a sintering-decarburization process. In this new process, first a SiC ceramic bonded carbon (SiC/CBC) is sintered in vacuum by spark plasma sintering, and then carbon particles in SiC/CBC are volatized by heating in air at 1000°C without shrinkage. The honeycomb structure has at least two different sizes of pores; ∼20μm in size resulting from carbon removal; and smaller open pores of 2.1μm remaining in the sintered SiC shell. The total porosity is around 70% and the bulk density is 0.93mg/m3. The bending and compressive strengths are 26MPa, and 105MPa, respectively. [Copyright &y& Elsevier]

Highlights: [•] Joining of AlN and graphite was achieved by SPS. [•] The effect of interlayer tapes contained either AlN and graphite or AlN was investigated. [•] Both tapes contained 5 mass%Y2O3 as sintering aid of AlN. [•] The maximum tensile strength of joints was obtained with the AlN-graphite composite. [•] AlN and graphite were joined physically with Al–Y–O phase during SPS. [Copyright &y& Elsevier]

Abstract: After placing SiC powder on an isotropic graphite substrate, the two materials were successfully joined by spark plasma sintering (SPS). The effect of an Al2O3–Y2O3 sintering aid on SiC during joining was studied. The tensile strength of the joints prepared at 1800°C under 30MPa for 5min reached 18MPa. The fracture occurred not at the interface, but at the graphite substrate. The joining mechanism of SiC/graphite is attributed to the following: after the SiC powder squeezes into the open pores of graphite during sintering, the sintered SiC produces a strong bond through the interface between SiC and graphite. [Copyright &y& Elsevier]

Abstract: A newly developed carbon-based composite, SiC ceramic bonded carbon (30vol% SiC) was directly clad with tungsten (W) at 1700°C by spark plasma sintering. There were no voids or cracks in the fabricated material. The adhesion strength between W and SiC/CBC is 90MPa and 33MPa by the bending and tensile test, respectively. The interface between W and SiC/CBC was analyzed and the cladding mechanism was discussed. [Copyright &y& Elsevier]

Abstract: To obtain light and tough materials with high thermal conductivity, AlN ceramic bonded carbon (AlN/CBC) composites were fabricated at temperatures from 1600 to 1900°C in a short period of 5min by the spark plasma sintering technique. All AlN/CBCs (20vol% AlN) have unique microstructures containing carbon particles of 15μm in average size and continuous AlN boundary layers of 0.5–3μm in thickness. With an increase in sintering temperature, AlN grains grow and anchor into carbon particles, resulting in the formation of a tight bonding layer. The AlN/CBC sintered at 1900°C exhibited a light weight (2.34g/cm3), high bending strength (100MPa), and high thermal conductivity (170W/mK). [Copyright &y& Elsevier]

Abstract: To obtain light, strong materials with high thermal conductivity, a new carbon-based material, AlN ceramic bonded carbon (AlN/CBC), was fabricated by combining gelcasting and spark plasma sintering techniques. The results showed that AlN/CBC (20vol% AlN) has a unique microstructure containing carbon grains of 15μm in size and an AlN grain-boundary layer of 0.5–3μm in thickness. Continuous AlN ceramic networks bonded the carbon grains together. Compared with the conventional AlN/carbon (AlN/C) material made by a ball-milling method, AlN/CBC showed a higher strength and a higher thermal conductivity by two and four times, respectively. [Copyright &y& Elsevier]

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 1–5vol% SiC-coated MWCNTs and successfully sintered at 1800°C by means of pulsed electric current sintering. These composites showed superior microhardness of 30.6GPa and toughness of 5.4MPam1/2 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 25.5GPa and 4.8MPam1/2, respectively. The SiC-coated MWCNTs/SiC composites showed an interesting behavior with the elastic recovery when undergoing an indentation test. [Copyright &y& Elsevier]

TiAl/Ti2AlC composites were produced by spark plasma sintering technology from mixed powders of Ti, Al and TiC. X-ray diffraction (XRD) patterns showed that the sintered products mainly consisted of TiAl and Ti2AlC phases. Electric probe microcosmic analysis (EPMA) photos indicated different microstructures depending on composition. In one case, when 7 vol.%TiC was mixed in the starting powders, the produced Ti2AlC particles were uniformly dispersed in the TiAl matrix with the partial lamellar structure containing γ and lamellar phases (duplex structure). In another case, while 15 vol.%TiC was added, the composites consisted of interpenetrating networks of Ti2AlC and TiAl phases. After the annealing, however, all of them changed to that of Ti2AlC particles dispersed uniformly in the γ(TiAl) matrix. The fracture toughness and bending strength of the composites were tested, respectively. [Copyright &y& Elsevier]

Three-dimensional electromagnetic or photonic crystals with periodic variations of the dielectric constants were fabricated by a rapid prototyping method called stereolithography. Millimeter-order epoxy lattices with a diamond structure were designed to reflect electromagnetic waves by forming an electromagnetic bandgap in the GHz range. Titanium oxide-based ceramic particles were dispersed into the lattice to control the dielectric constant, resulting in the formation of narrow and deep bandgaps. Crystals of the inverse form that have a network of holes with the diamond structure in a dielectric matrix were successfully fabricated as well. These inverse diamond structures formed the perfect bandgap reflecting electromagnetic waves for all directions. The location of the bandgap agreed with the band calculation using the plane wave propagation method. [Copyright &y& Elsevier]

Abstract: 3D Micro welding (3DMW) is a newly developed rapid prototyping method for metals. It is a combination of micro tungsten inert gas (micro-TIG) welding and a layered manufacturing method. The tip of a thin metal wire is melted by a micro-TIG welder to form a small metal bead. By building up metal beads layer by layer under computer control, a 3D metal object is eventually formed. The fabrication of simple 3D objects made of Inconel alloy 600 was studied. The interface between adjacent beads had good adhesion. No cracks or pores remained in the formed objects. The tensile strength, elongation, density, and Vickers hardness were measured and compared to those of the commercial superalloy. The obtained results suggest that actual micro components or tools of refractory metals with high strength and oxidization resistance can be formed without molds by 3DMW. [Copyright &y& Elsevier]

Abstract: 3D micro-welding (3DMW) is a newly developed rapid prototyping method for metals. It combines a micro-tungsten inert gas (TIG) welding with a layered manufacturing method. A tip of a thin metal wire is melted by a micro-TIG welder to form a small metal bead. By building up metal beads layer by layer under computer control, a 3D metal object is eventually formed. A wide variety of metals and alloys can be used. The Ti–Al based intermetallic alloys have superior mechanical and chemical properties. However, the forming process is difficult and costly. We have tried to fabricate 3D objects of the Ti–Al alloy system by using several thin Ti and Al wires. Some simple objects with a unique microstructure or graded composition are demonstrated. [Copyright &y& Elsevier]

Abstract: Fabrication process for three-dimensional ceramic photonic crystals with a diamond structure was investigated. A diamond structure composed of epoxy lattice including SiO2–TiO2 ceramic particles at 10vol.% was fabricated as a precursor by stereolithography. After burning off the epoxy resin in air, the diamond structure of SiO2–TiO2 was successfully sintered at 1400°C for 2.5h. The linear shrinkage ratio was 50%. Cracks were not found in the sintered diamond structure. Photonic bandgap was observed at around 19GHz. [Copyright &y& Elsevier]

The article describes the case of a 38-year-old woman with multiple epiphyseal dysplasia (MED) who underwent an osteochondral autograft for localized chondral lesions of bilateral medial femoral condyles (MFC) in order to preserve the articular surface and joint function. It reports on the 10-year follow-up of this procedure which is believed to be the first report of an osteochondral autograft for chondral lesions of the knee in a patient with MED.

Abstract: Single-phase β-sialon powders (z =2–4) have been prepared with homogeneous compositions by the combustion synthesis. The raw materials (Si, Al and SiO2) were combusted under N2 pressure of 1MPa. Without using a diluent, the reaction temperatures were very high (>2000°C) and the combustion products contained Si and Al residues. With addition of commercial β-sialon (z =1) as a diluent (up to 50wt%), both the reaction temperatures and amount of residual Si and Al significantly decreased. The combustion reactions completed at 50wt% dilution, and pure β-sialon phases were synthesized. When the combustion product itself is used instead of the commercial diluent, the phase content of desired z value increased with the repetition times until a single-phase powder is produced. The sinterability of the synthesized powders was then tested using 5wt% Y2O3 as a sintering aid by the spark plasma sintering (SPS). [Copyright &y& Elsevier]

Abstract: Uniform quasi-aligned AlN nanowhiskers grown in the reacting Al particles have been successfully prepared in high content by combustion synthesis using NH4Cl as a morphology-controlled promoting additive. FE-SEM and TEM images show that the nanowhiskers, which are single-crystalline hexagonal wurtzite AlN growing along [001] direction, have diameters in the range of 80–170nm and a length of several to several tens of micrometers. The effect of NH4Cl on the growth of nanowhiskers was discussed. It was found that NH4Cl not only controlled the products’ morphology, but also changed the combustion behavior and nitridation mechanism in the combustion synthesis process. [Copyright &y& Elsevier]

Abstract: Carbon-matrix composites with self-assembly interconnected carbon nano-ribbon networks were fabricated using natural and inexpensive rice husks by impregnating the rice husks with transitional metal solutions and sintering. The nano-structure of the composite was characterized using transmission electron microscopy. The electromagnetic interference shielding effectiveness of the composite was evaluated in the frequency range of 30kHz–1.5GHz. The electrical conductivity was measured as a function of the sintering temperature. These characteristics were compared with those of carbon-matrix composites without nano-ribbon networks. [Copyright &y& Elsevier]

Abstract: Manganese doping of gallium oxynitride was investigated to obtain a magnetic semiconductor by nitriding a precursor in ammonia flow. The precursor was obtained by prefiring a mixed gel made of Mn2+ and Ga3+ nitrates and citric acid in aqueous solution. The products were isostructural with hexagonal GaN. The doping limit was 10 and 5at% in the samples nitrided at 750 and 850°C, respectively. Chemical analysis of the products suggested that they were manganese doped gallium oxynitrides. Oxide and nitride ions were randomly distributed in the anion sites in the latter product. Manganese oxide cluster might be formed in the former. The product nitrided at 850°C showed an antiferromagnetic interaction with a Weiss temperature θ =−38K, while the product nitrided at 750°C was paramagnetic. [Copyright &y& Elsevier]

Abstract: Dense diamond/cemented carbides were fabricated at around 1300°C, 41MPa for 3min under meta-stable conditions for diamonds by pulsed-electric current sintering. Diamond particles were coated with SiC to prevent the graphitization of diamond with molten binder during sintering. No graphitization of diamond was confirmed by microstructure observation and Raman scattering analysis. The combination of SiC coating of diamond and rapid sintering was effective to fabricate diamond/cemented carbides. These new materials, composed of diamond and cemented carbide, showed a 50% larger fracture toughness and 10 times better wear resistance compared with conventional cemented carbides, and five times better machinability compared with diamond compacts. The diamond/cemented carbides are applicable to wear-resistant sliding tools such as centerless blades, work rests, and stoppers. [Copyright &y& Elsevier]

Abstract: Photonic fractal with self-similar structure of dielectric medium can strongly localize the electromagnetic wave energy in the three-dimensional fractal structure. We have fabricated Menger-sponge fractal structures of epoxy by using stereolithography. Titania–silica particles were dispersed into the epoxy to increase the dielectric constant and decrease the dielectric loss. The samples have square holes of 1, 3, 9 and 27mm in edge length through the cubic body of 81mm. Four types of Menger-sponge samples with fractal stages 1–4 were subjected for measurement of microwave responses. The both reflection and transmission amplitudes were attenuated simultaneously at frequencies of 9.5, 10.5, 12.0 and 13.5GHz for each sample with fractal stages 1, 2, 3 and 4, respectively. The electromagnetic field amplitudes in the air holes measured by inserting a mono-pole antenna probe confirmed the strong localization of the electromagnetic wave in the central air cavity. The localized mode frequency can be calculated using the sample size, number of stage, and the effective dielectric constant. The localization efficiency increased according to the fractal stage number. [Copyright &y& Elsevier]