Metallic lattice structures are focused on as an excellent energy absorbing material. Their energy absorption property strongly depends on the ductility of the base material as well as the cell structure. The present study proposes new metallic lattice structures made of superplastic alloy. Sn-Bi eutectic alloy which shows typical room-temperature superplasticity was used for the base material. Lattice structures with the porosities of 72-75% were successfully manufactured through precision casting process. The resin mold was additively manufactured using a vat photopolymerization apparatus. Compression tests were carried out with different compression speeds. The Sn-Bi alloy lattice structures showed relatively high strain rate sensitivity exponent at low strain rate region. High energy absorption property was achieved at low strain rate region. Experimental results indicate that the superplastic deformation of the base material is effective to increase the energy absorption property of lattice structures.

Anodizing aluminum is widely used for various industrial applications such as corrosion protection, hardness enhancement, and coloring. However, when the anodized aluminum is exposed to high temperatures, many cracks form in the anodic oxide layer. Therefore, a deep understanding of crack formation behavior is essential for using anodized aluminum at higher temperatures. In the present investigation, the effect of the micro- and nano-structures of porous anodic aluminum oxide on the formation behavior of cracks in its oxide due to heat treatment at 523 K was investigated. High-purity aluminum plates and A6016-T4 aluminum alloys were anodized in sulfuric and oxalic acid solution to form a porous oxide film. Heat-treatment of the porous oxide with a hydrated layer formed by pore sealing leads to the formation of many cracks. Whereas the film thickness and sealing time have a significant effect on the crack formation behavior during heating at 523 K, the nanostructures of the porous oxide, such as the barrier layer thickness and pore size hardly contribute to the formation of cracks. These cracks formed in the porous oxide during heating may result from the difference in the amount of the hydrated oxide at the outermost surface and pore bottom of the oxide, and thus result uneven elongation during thermal expansion. The porous oxide with higher heat and corrosion resistance could be successfully fabricated by optimizing the pore sealing time for 15 min and temperature at 373 K.

Microscopic stress-strain curves were obtained by applying stress measurements using the HR-EBSD method and strain measurements using the DIC method to the same field of view in SEM in-situ tensile tests. From the analysis of these microscopic stress-strain curves, yield stress map and work hardening rate map were successfully produced. The relationship between these mechanical property value maps and the microstructure is investigated. The yield stress maps confirm the tendency of the local yield stress to show different values for different grains, but the Schmid factor alone cannot explain the magnitude of the yield stress. When adjacent grains with significantly different Schmid factors deformed cooperatively, the yield stress is found to increase as a result of stress partitioning. Localized regions of extreme work hardening rates were observed in the work hardening rate maps. These regions were located close to grain boundaries with low m′ values where slip transfer was difficult and an interruption of the slip bands was observed. In addition, the rate of increase of GND density with strain was large in these regions. From these results, it can be understood that the extreme work hardening rates are due to increased back stresses caused by the accumulation of dislocations on low m′ grain boundaries.

The microstructure and chemical composition of iron phosphate conversion coatings were investigated by surface/cross-sectional observation using FE-SEM/STEM and chemical state analysis using XPS. As a result, it was suggested that the conversion reaction progressed while the surface oxide on the base material remained, and the fine particles of coatings components were deposited and agglomerated to cover the material surface. The upper layer of coatings was mainly composed of iron phosphate, while the interface between the coatings and base material was deposited iron oxide. The proportion of iron phosphate and iron oxide was almost equal at the initial stage, and the amount of iron phosphate increased as the coating thickness.

In recently years, hydrogen production by water electrolysis using renewable energy is promoted from a carbon-neutral perspective. However, hydrogen is difficult to store and transport, and low volumetric energy density. Therefore, ammonia obtained by the Haber-Bosch process is attracting much attention as an energy carrier because of its easy liquefaction and handling. Ammonia is toxic, but it can be detected easily if ammonia leaks outside owing to its characteristic smell. Thus, a direct ammonia fuel cells (DAFCs) that use ammonia as fuel is promising candidate as a new power generation system. Generally, Pt is used as anode catalyst for ammonia oxidation reaction in DAFC. But it is desired to develop an alternative catalyst for DAFC anode due to the price escalation of Pt, limitation of Pt reserves and the problems of inactivation caused by N_ads poisoning on Pt. Therefore, Pt-Mo alloy catalyst was prepared by RF-magnetron sputtering and the ammonia oxidation activity was investigated in this study. Pt-Mo alloy catalysts showed higher ammonia oxidation activity than Pt one. Especially, Pt-44.0at％Mo indicated 31.4 mA cm⁻² and it is the highest activity among Pt-Mo alloys. And then, Pt-44.0at％Mo is promising candidate for anode catalyst of DAFC.