Aluminum nitride nanopowder was fabricated from transition alumina nanopowder by gas reduction-nitridation method. It was sintered by spark plasma sintering with 1 wt% Ca_3Al_2O_6 as a sintering additive in nitrogen. A so-called nanoceramic was obtained by sintering at 1450℃ with Ca_3Al_2O6_, though the nanopowder without additive was densified at 1550℃. The sintering temperature for dense aluminum nitride ceramic could be reduced by 1 wt% Ca_3Al_2O_6 as a sintering additive.

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As a key technology in future earth observation and astronomical missions, a large-scale lightweight mirror constructed of silicon carbide-based material has been studied at JAXA. Silicon carbide was selected as the most promising candidate due to excellent characteristics of high specific stiffness and low CTE. One of the most important technical issues for large-scale ceramic components is quality stability (viz. differing in material property depending on part and processing) that might influence thermal and/or structural reliability due to unforeseen deformation and breakage. In this study, a propositional approach for the quality assurance technique of a practical flight mirror was examined, in which coupon samples extracted from various parts of the surrounding area of a newly manufactured φ800mm mirror were put to evaluation for estimating basic physical characteristics and homogeneity.

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CNT dispersed Si_3N4_ ceramics with double percolation structure were prepared by using granules of Si_3N_4 powder with and without CNTs followed by densification through spark plasma sintering process. Although the single percolation sample having 0.5wt% CNT was insulator because it was below percolation threshold, the electrical conductivity was showen in the double percolation sample having 0.5wt%. Consequently, it was shown that the electrical conductivity of CNT dispersed Si_3N_4 was able to be controlled by double percolation.

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The effect of binder segregation in alumina granules on strength of green compacts was investigated. The thickness of sgregated binder layer affected the strength of the green compact as well as the granule itself. The addtive concentration of 5.0wt% polyacrylic acid type binder to alumina granules served segregated binder layer on the surface of granules. This layer disappeared when the binder concentration was less than 2.5wt%. The fracture strength of a granule with 5.0wt% PAA binder was much lower than that of green compacts made from the granules. In the case of 2.5wt% PAA binder concentration, on the other hand, the fracture strength of a granule was higher than that of the green compacts. This result was consistent with that of the fracture surface in which differenct fracture mechanisms was observed between the green compacts with 2.5wt% and 5.0wt% of PAA binder.

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Strength variation of alumina ceramics formed by dry-pressing of granules was examined by the number density of coarser defects. In simulation, the Weibull modulus m was related to the exponent n of the power function of the number density of coarser defects; m = 1.8n - 1.9. Average strength was also related to parameters A and n. The number density of coarser defects in alumina ceramics was measured by the direct observation of the thinned sample using the optical microscopy. The coarser defects density was expressed by the power functions. The Weibull modulus and strength of alumina samples were coincident well with the simulated data.

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In this study, carbon nanofiber (CNF) reinforced Al_2O_3 composites were fabricated. To fabricate uniformly-dispersed CNF/Al_2O_3 powder, electrostatic adsorption, which could increase the surface potential of CNFs, was applied. Al203 sol was then adsorbed onto the surface of CNFs uniformly. The mixed powder was sintered by spark plasma sintering under the pressure of 50 MPa at 1600℃ in Ar atmosphere. Fracture behavior of the specimen was evaluated by bending test, indentation test and fracture-surface observation. The results showed that the bending strength of specimen was lower than monolithic Al_2O_3. It might be because there were many pores and the interface between CNF and Al_2O_3 were relatively weak. However, a large number of pull-out and bridging of CNFs were observed by the fracture surface observation with a scanning electron microscope. This suggests that CNFs could improve the fracture toughness of the CNF reinforced Al_2O_3 composites.

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In this study, delamination behavior of Thermal Barrier Coating (TBC) used in a high temperature component in a land based gas turbine was investigated experimentally and analytically. In the experiments, tensile test at some temperature conditions and fatigue test were performed. Two modes of crack initiation system could be observed depending on temperature. One mode was the crack initiating at bond coat/substrate interface and the other mode was the crack initiating at top coat/bond coat interface. It was found that delamination occurred in the segment between cracks and the delamination propagated along top coat/bond coat interface, which were depending on creep deformation.

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Tribological properties of textured cemented carbide treated with fine particle peening were evaluated using a ring on disc type testing apparatus in boundary lubricated condition. The cemented carbide consisted form tungsten carbide (WC) and cobalt (Co) and the chromium alloy steel (SUJ2) disc was used for the specimen. The developed micro shot peening system consisted from the double walled nozzle and the storage tank contained rubber balls with media was applied to fabricate the texture consisted from micro dimples on the disc surface. The friction experiment was carried out with a cast iron ring at a constant sliding speed of 0.1 m/s and various applied loads from 100 to 1200 N. Results showed that the friction coefficient mated with the ring having truncated parallel grooves was smaller and that the higher load capability was obtained using higher hardness of the disc.

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A novel tribo-coating method was developed to improve tribological properties of steel surfaces. Molybdenum layer was synthesized by rubbing steel surface with high-speed- rotating brush made of molybdenum wire. Formation of the molybdenum tribo-layer was confirmed by SEM/EDX analysis. The tribological properties of the modified surfaces were evaluated by using the SRV sliding tester under lubrication with a base-oil (PAO) and a model lubricant (PAO with additives (ZnDTP+MoDTC)).

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Visualization of impact-friction surfaces of elastomers using a total reflection method were carried out in order to investigate the dynamics of elastomers on such surfaces. In the wet condition relative intensity at the contact center is gradually decrease toward that of the dry condition with waiting time while apparent contact area is not quite different from that of the dry condition. Stick-slip is generated on the impact-friction surfaces only in the wet condition. In that time, relative intensity at the contact center is higher than that of dry condition; this indicates that stick-slip is induced by water being between the contact surfaces.

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