Papers by Author: Yutaka Kagawa

Abstract: Multi-scale grid is an essential deformation carrier in optical methods for multi-scale deformation measurement. In this study, several new-type multi-scale grids were designed and fabricated by electron beam lithography. Each pattern includes several periodically distributed dots with the same spacing but different sizes. As a consequence, the grayscale of the whole grid pattern periodically changes. The peak parts of the grayscale generate a secondary grid, i.e., the large-scale grid. The ratio of the large-scale grid pitch to the small-scale grid pitch can be easily adjusted according to the requirement. The natural integration between the small-scale grid and the large-scale grid works well in eliminating the mutual disturbance between the different-scale grids. Besides, this type of grid has a very high success rate in fabrication owing to the small differences in size between the big dots and the small dots. The proposed multi-scale grid pattern is expected to serve as the deformation carrier in moiré methods and geometric phase analysis for multi-scale deformation measurement.

Abstract: PAN and Pitch short carbon fiber-reinforced SiC matrix composites were fabricated by using a melting infiltration technique. The microstructure of the composites was characterized by scanning electron microscopy. The flexural strength of the composites was measured at room and high temperatures. The thermal conducitivity of the composites were evaluated. Effects of fibers on mechanical properties and thermal conductivity were assessed. The experimental results showed that the silicification of fibers during siliconizing was prevented due to the presence of barrier layer on the surface of fiber. Also, flexural strength and thermal conductivity depended on fibers used and content of fibers.

Abstract: Hydrolysis and dispersing behavior of aqueous ZrB2 slurry were investigated. The isoelectric point (IEP) of ZrB2 slurry was measured to be pH 6.3. The acid and base slurry underwent rather rapid change of pH after fabrication for one and three hours, respectively. The oxygen content of the boride powder increased slowly with static ageing time in acid and neutral slurries, while the value decreased in base slurry. Application of poly(ethyleneimine) changed IEP of the boride slurry to pH 10.4. Sedimentation test informed that stability of the slurry was improved when increasing the molecular weight of poly(ethyleneimine) to 70,000 and in acid slurry (pH 3).

Abstract: We report sintering additive systems to decrease the densification temperature of the corrosion resistant AlN-SiC-TiB2 system. Since oxide additives degrade the high temperature properties of the system, and other kinds of metallic additives may affect the formation of protective mullite during oxidation, only the constituent elements were applied as additives. Dense samples ( > 98 % relative density) could be fabricated at 1850 oC and 1900 oC by spark plasma sintering (SPS) and hot pressing method, respectively.