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To obtain light and tough ceramic bonded carbon (CBC) materials with high thermal conductivity SiC Ceramic bonded carbon (SiC/CBC) is developed using Si_3N_4 and carbon powders (30:70 in volume ratio) and sintering by spark plasma sintering at temperatures of 1900℃. The SiC/CBC were highly dense (98% theoretical density), lightweight (2.42 Mg/m³), and had both relatively high bending strength and thermal conductivity (150 MPa and 138 W/mK, respectively). Moreover, the SiC/CBC could be joined tightly with W. The joints of SiC/CBC and W may be used as heat-sinks for W-based plasma facing components. The joining strength between W and SiC/CBC was 33 MPa when measured by a tensile test and 90 MPa by a bending test.

To obtain light and tough materials with high thermal conductivity, ceramic bonded carbon (CBC) composites consisting of carbon particles and thin ceramic boundaries were developed. The AlN ceramic bonded carbon (AlN/CBC, 20vol% AlN) could be densified by spark plasma sintering or hot-pressing, and exhibited light weight (～2.34 Mg/㎥), high bending strength (～100 MPa), and high thermal conductivity (～170 W/mK). AlN/CBC could also be joined strongly with ceramic (AlN) and some metals (W) due to its unique microstructure. These results suggest that the AlN/CBCs have large potential to be used as structural components and heat sinks for electrical and plasma facing devices.

The new carbon composites which we named Ceramic Bonded Carbon (CBC) consist of carbon grains bonded with ceramic grainboundaries. The CBC structure can protect carbon against oxidation and improve the strength due to the three dimensional network of ceramic grainboundaries. We have developed two processing routes for different CBCs. One is for a SiC/CBC which was fabricated by SiC coating on carbon particles through the reaction of SiO vapor and carbon at 1500°C in vacuum and their consolidation at 2000°C for 20 min using a pulsed electric current sintering. Another approach is for a Si₃N₄/CBC by gelcasting, the preform of CBC and consolidation at 1500°C for 5 min. Both CBC compacts exhibited similar microstructures to the CBC model having the ceramic grainboundaries of SiC and Si₃N₄ with thicknesses below 3μm. They had the bulk density in the range of 2.2 to 2.5 g/㎤, relative density of about 90%, bending strength of 115 to 150 MPa, and electrical resistivity of 60 to 1800 μΩm. These results suggest that the CBCs have a large potential to extend the performance and application of carbon materials.

Smart processing is a new concept of materials processing aiming to produce new material functions or improve performances through fine controlling and minimizing process energy and resources. We are developing various 3D micro ceramic devices by using CAD/CAM stereolithography and successive sintering as smart processing. Design and processing of micro gears and photonic crystals made of dense ZrO2 toughened Al2O3 (ZTA) and Al2O3 toughened SiO2 composites are demonstrated as well as their final mechanical and electromagnetic properties.

This investigation describes novel growth of quasi-aligned aluminum nitride (AlN) nanofibers by the self-propagating high-temperature synthesis (SHS) under low nitrogen pressure. The starting charge consists of Al and AlN diluent (40/60 mole%) with a mixture of Y₂O₃ and NH₄Cl additives (5wt% each). The combustion reaction was performed under 0.25 MPa N₂ pressure. The microstructure of as-synthesized AlN powder consists of two major types; aggregates of irregular particles (~0.5 μm, the same as the original AlN diluent) and balls-like grains (same size and shape as original Al particles) consisting of a thin crust (≤150 nm) covering unique quasi-aligned AlN nanofibers grown in the interior. This powder can be easily consolidated to near theoretical density without sintering additives in a period of 5 min at 1600 ℃ using the spark plasma sintering (SPS) process. The microstructure of sintered AlN was homogeneous with dual morphologies of many ultrafine sub-grains (fibers, nanometer size in diameter) aggregated in large grains. The thermal conductivity was 91 W/m-K.

A novel freeform fabrication method for refractory metals named 3D Micro Welding (3DMW) has been proposed, which is rapid prototyping combined with TIG (Tungsten Inert Gas) welding. Formation of beads and simple pin objects composed of Ti-Ni and Ti-Fe intermetallic alloy phases was attempted. As the peak arc current increased from 5A to 30A, the bead diameter increased in both systems. Ti, Ti₂Ni and TiNi phases were formed in the Ti-Ni system, and Ti, TiFe and TiFe₂ phases in the Ti-Fe system. Simple intermetallic alloy pin objects of these two systems were formed by alternate stacking of their component wires and their microstructures were observed. No pores or cracks were observed and the uniform composition remained. Exothermic SHS reactions should take place and assist the intermetallic alloy formation. 3D titanium objects of ring and double helix shapes were formed directly from their computer models without using molds or dies.

3D fractal structures, which we have named photonic fractals, can strongly localize electromagnetic wave with a specific wavelength associated with the geometry and physical properties of the fractal structures. The photonic fractals can be fabricated with various materials including polymers, ceramics, metals, and their composites. The localization mechanism in a photonic fractal with self-similar structure is essentially different from the localization in a photonic crystal with a periodic structure. This new material is considered to be applicable in a wide area of communication, information, energy, sensing, medical care, and other fields.

Three-dimensional photonic crystals with periodic variations of the dielectric constant were fabricated by using a rapid prototyping method called stereolithography. Millimeter-order epoxy lattices with a diamond structure were designed to reflect electromagnetic waves by forming an photonic bandgap in the GHz range. Titania based ceramic particles were dispersed into the lattice to control the dielectric constant. The diamond lattice structures formed the perfect bandgap reflecting electromagnetic waves for all directions. Diamond structures with stretched lattice spacing were successfully fabricated as well, resulting in the directional transmission of microwaves. A microwave antenna head composed of the normal and stretched diamond structure was fabricated and achieved unidirectional transmission.