Silver powder was prepared through water atomization at 1280℃ under the nitrogen atmosphere. As-prepared silver powder consisted of various particles with morphologies such as spherical, irregular and coarse and had high crystallinity. Relationship between the volume average particle size (D₅₀) of silver powder and production factors was investigated. In this work, the production factors such as atomization pressure, angle, nozzle diameter, suction amount of air and water temperature were selected to verify the influence on D₅₀. It was found that D₅₀ decreased with decreasing atomization pressure, angle, nozzle diameter and water temperature. When the atomization pressure was 100 MPa, the uniform water stream was disturbed and then D₅₀ became higher. On the other hand, it was confirmed that D₅₀ decreased with increasing suction amount under reduced pressure. Crystallite size and crystallinity of silver powder increased with decreasing water temperature.

The production processes of old Japanese coins, Genbun-koban, Akita-ginban and Morioka-ginban, were studied. These coins were manufactured by a forging method in the Edo-era. Genbun-koban, manufactured at a gold mint of the Tokugawa shogunate called Kinza, in 1736, is made of Au-Ag alloy and its surface is not flat. The residual stress of this coin is compressive, and the residual stress in the stamped area is higher than that in the flat area. The Iroage method was used to color the coin; it is a thermal treatment, resulting in lows the residual stress is smaller at flat area. Akita-ginban, manufactured in the Akita domain in 1863 is made of pure Ag and its surface is also not flat. There is no residual stress in this coin. This result shows that the thermal treatment of this coin was carried out after processing. Morioka-ginban, manufactured in the Morioka domain in 1868, is made of pure Ag, and its surface is flat. The residual stress of this coin is compressive, and the residual stress in the stamped area is higher than that in the flat area. This result shows that the thermal treatment was not carried out after processing. These coins manufactured in the Edo-era thus had different thermal treatments.

Ni polycrystals were processed by accumulative roll-bonding (ARB) of 7 cycles and tensile specimens were cut from the ultra-fine grained (UFG) Ni after ARB. Microstructure and crystallographic orientation of UFG Ni were observed by scanning electron microscopy (SEM) and electron back scattering diffraction (EBSD) method. Three textures component, Copper, Brass and S orientations were found in UFG Ni.

Three specimens for tensile tests having tensile directions parallel with RD, TD and 45D were cut from UFG Ni. RD and TD indicate rolling and transverse directions of ARB process respectively, and 45D indicates a 45 degree direction between RD and TD. For these specimens, in-situ XRD measurements were performed during tensile deformation. Elastic strains during tensile deformation were calculated from values of peak shift for various diffraction planes obtained by the XRD measurements. For RD specimen, the elastic strains during initial deformation for various diffraction planes were almost the same. However, for 45D specimen, the elastic strains for various diffraction planes were different even at initial loading. TD specimen showed behavior like RD specimen. The difference in the elastic behavior between the specimens are discussed by considering difference in crystallographic directions of grains along tensile directions in the specimens which is caused by the textures generated after ARB.

Recrystallization, grain growth, and particle ripening behaviors of pre-deformed Fe-In alloy specimens in liquid-particle dispersion microstructures were investigated by microstructural observation. Liquid In particles were trapped by grain boundaries of recrystallized grains, and the trapped particles were dragged by the grain boundaries during grain growth. The recrystallization and the grain growth of the αFe matrix were extremely retarded by the addition of In. The controlling diffusion mechanism of the growth of matrix grains and the ripening of intergranular liquid In particles changed from interfacial diffusion between matrix and particles to impurity diffusion through liquid In particles with increasing volume fraction of liquid In particles.

Mater. Trans. 59(2018) 188-197に掲載

Non-destructive damage evaluation of rocket engine combustion chamber was investigated by using replica method through rapid setting silicon rubber molding agent. Scratch marks, grinding marks and an oxide film on the combustion side surface of the repeated burning test were successfully transferred to this replica sheet without complicated surface treatment. Observation results of the sampled replica showed the traces of the oxide film formation, disappearance of the grinding marks and crack formations on the oxide films due to redox reaction during repeated uses. The surface roughness of light and dark lines parallel to the cooling grooves with cracked oxide film was evaluated by laser scanning microscope. The surface roughness parameter could be useful to evaluate the damage of the reusable sounding rocket engine.