[en] The effect of Cu-addition on age-hardening and precipitation have been investigated by hardness measurement, tensile test, high resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) techniques. Higher hardness, strength, and lower elongation were caused by increasing amount of Zn + Mg because of increased number density of precipitates. Cu addition also provided even higher peak hardness, strength, and lower elongation. The alloy containing highest Cu content had fine precipitates of GPB-II zones or the second clusters, in the precipitate free zones (PFZs) and the matrix, together with η′/η in the matrix from the early stage of aging. Two regions have been confirmed as the PFZs in the peak aged alloy containing highest Cu: (1) nearest to grain boundary (GB) about 70 nm in width (n-PFZ) and (2) conventional PFZ about 400 nm in width which can be confirmed by conventional TEM (con-PFZ). The con-PFZ contains fine precipitates consisting of GPB-II zones or the second clusters, even for 2 minutes of aging at 473 K which were not present in the n-PFZ. The fine precipitates, GPB-II zones or the second clusters in the con-PFZ and the matrix disappeared at overaged condition. (author)

[en] Highly functional and multifunctional material surfaces may be created through fabrication of unusual surface structures. We fabricated mushroom-like nanostructures on a stainless steel surface by simple processes: heat treatment under an atmosphere of low partial pressure of oxygen, followed by electrochemical etching. Island-like titanium oxide was formed on the Ti-containing stainless steel surface by selective oxidation during heat treatment. The titanium oxide became the cap part of the mushroom-like nanostructure and the stem part was fabricated by selective dissolution during electrochemical etching. Detailed analysis revealed that the cap part of the mushroom-like nanostructure was mainly composed of γ-Ti₃O₅, and the stem part was composed of the stainless steel substrate. The contact resistance was significantly reduced by the fabrication of the mushroom-like nanostructures. The protrusions of electrically conductive γ-Ti₃O₅ can contribute to the reduction of the contact resistance. The mushroom-like nanostructures improved the hydrophilicity of the surface without fluorine coating, but improved the hydrophobicity of the fluorine-coated surface. The contact between the stainless steel surface and the water droplet was in the Wenzel state. (author)

[en] In recent years, it has been reported that intermetallic compound particles can suppress hydrogen embrittlement by hydrogen trapping. Some intermetallic particles in aluminum alloys, such as Al₇Cu₂Fe, have internal hydrogen trap sites; it is proposed that hydrogen embrittlement can be suppressed by preferential hydrogen partitioning in these sites. However, intermetallic compound particles act as fracture origin sites, and excessive addition degrades the mechanical properties of the material. In this study, we quantitatively evaluated the damage and decohesion behavior of intermetallic compound particles in high-hydrogen content 7XXX aluminum alloys by using in situ synchrotron radiation X-ray tomography. The results revealed that the hydrogen particles induced early high-strain localization, and the Al₇Cu₂Fe particles were damaged in that region due to its brittleness, resulting in early fracture. Hydrogen had no effects on the fracture and debonding behaviors of intermetallic compound particles, suggesting that the observed particle brittle fracture is dependent on their mechanical properties. (author)

[en] Neutron scattering experiments were conducted to reveal the origin of diffuse scattering in a medium-entropy alloy (MnCoNi). Results showed that a time-temperature-dependent short- and long-range structural transformation from a face-centered cubic to a primitive tetragonal structure occurs. In the MnCoNi alloy, the long-range ordered phase with a relatively small c/a ratio of 3.7(1)% can only be grown in a limited temperature range, whereas short-range structural transformation with a short correlation length of 1-4 nm can be formed in a wide temperature range. On the contrary, no sign of short-/long-range staggered atomic rearrangement, such as L1₀ and L1₂ structures, was observed in the CrCoNi alloy at least at room temperature. The difference in the forming ability of short-/long-range ordering between the MnCoNi and CrCoNi alloys was discussed. (author)

[en] Recent research has shown that some intermetallic compound particles with high interfacial hydrogen trap energies (e.g., Mg₂Si) are prone to damage at high hydrogen concentrations. In this study, the acceleration of particle damage in an A6061 alloy was observed in-situ via X-ray CT. The damage behavior of the particles that are located in the crack tip stress field, where high stress triaxiality causes a local increase in the hydrogen concentration, was analyzed. The influence of hydrogen on the damage behavior of the dispersed Mg₂Si particles was investigated by preparing a material charged with hydrogen to achieve extremely high hydrogen concentration, and further hydrogen enrichment in a crack tip region was also utilized. Interfacial debonding of Mg₂Si particles was frequently observed in the vicinity of a crack tip immediately prior to tensile fracture. Even though the fracture is typical of ductile fracture, hydrogen accelerates particle damage and reduces the macroscopic ductility of the aluminum alloy. This can be considered as a form of hydrogen embrittlement of aluminum alloys. Even in materials with relatively low hydrogen concentrations (0.85 mass ppm), interfacial debonding occurred in the hydrogen-enriched crack tip regions. A higher hydrogen concentration promoted interfacial debonding over a wider range of particle sizes and particle shapes. It can be inferred that localized hydrogen enrichment, which is expected to occur due to external hydrogen exposure, stress corrosion cracking, corrosion or crack tips, can directly contribute to debonding at the Mg₂Si particle/aluminum matrix interface. According to the analysis, reduction of the diameter and simplification of the shape of Mg₂Si particles are effective method for suppressing such hydrogen-induced debonding. (author)

[en] Bulk samples of Ni_3Nb and Ni_3Ta intermetallic compounds were irradiated with 16 MeV Au, 4.5 MeV Ni, 4.5 MeV Al, 200 MeV Xe and 1.0 MeV He ions, and the change in near-surface lattice structure was investigated by means of the grazing incidence x-ray diffraction (GIXD) and the extended x-ray absorption fine structure (EXAFS). The Ni_3Nb and Ni_3Ta lattice structures transform from the ordered structures (orthorhombic and monoclinic structures for Ni_3Nb and Ni_3Ta, respectively) to the amorphous state by the Au, Ni, Al and Xe ion irradiations. Irrespective of such heavy ion species or energies, the lattice structure transformation to the amorphous state almost correlate with the density of energy deposited through elastic collisions. In the case of the samples irradiated with 1.0 MeV He ions, however, no amorphization was observed even when the density of elastically deposited energy is the same as that for Au irradiated sample which showed the amorphous phase. The change in Vickers hardness induced by the amorphization was also measured and was discussed in terms of ion fluence and the density of deposited energy. (author)

[en] Electron backscatter diffraction (EBSD) measurements were performed for welded 308 stainless steel corroded under proton irradiation at 473 K. After chemical cleansing and subsequent mechanical polishing to remove oxide layers on the specimen surface for EBSD measurements, selective dissolution of delta ferrite (δ) phase in the dendritic microstructure was detected only for the in-beam corroded specimen. The susceptibility to δ phase dissolution is dependent on the deviation angle of its orientation from the (101) plane on the specimen surface when δ phases are in a grain of austenitic gamma (γ) phase as well as on the γ-γ phase grain boundaries except for the coincidence grain boundaries. Selective dissolution of δ phase would be explained by not only radiolytic products such as radical oxygen acting as electric charge carriers but also the radiation-induced point defects and dislocation structures playing an important role in sustaining anodic reactions at δ phases. (author)

[en] The FeCrAl-ODS alloy claddings were manufactured and Vickers hardness, ring tensile tests and transmission electron microscopy (TEM) observations of these claddings were performed to investigate the effects of thermal aging at 450°C for 5,000 and 15,000 h. The age-hardening of all FeCrAl-ODS alloy cladding was found. In addition, the significant increase in tensile strength was accompanied by much larger loss of ductility. It was suggested that this age-hardening behavior was attributed to the (Ti, Al)-enriched phase (β′ phase) and the α′ phase precipitates (content of Al is <7 mass%). In comparison with FeCrAl-ODS alloys with almost same chemical compositions, there was significant age-hardening in both alloys. However, the extrusion bar with no-recrystallized structures was keeping good ductility. It was suggested that this different behavior of reduction ductility was attributed to the effects of grain boundaries, dislocation densities and specimen preparation direction. (author)

[en] The stability and electronic structure of enargite-type Cu₃AsO₄ were investigated through first principles calculations. Although its synthesis has not been reported to date, the calculations indicate the possibility of synthesis of enargite-type Cu₃AsO₄. Enargite-type Cu₃AsO₄ is expected to possess a 1-1.2-eV band gap and a large optical absorption coefficient comparable to those of absorber materials for thin-film solar cells such as CdTe and GaAs. Enargite-type Cu₃AsO₄ is also expected to exhibit both p-type and n-type conduction by appropriate impurity doping. This property will enable use of this material in a p-n homojunction. In contrast, enargite-type Cu₃AsS₄ exhibits p-type conduction whereas n-type conduction is not expected. The results of this study indicate that enargite-type Cu₃AsO₄ is very promising as an absorber material for thin-film solar cells. (author)

[en] A novel equiatomic CoCrNiTiV high entropy alloy was fabricated by a vacuum arc-melting, and investigated from the view of phase component, microstructure, mechanical properties. The results experimentally displayed that a typical single phase BCC solid solution was acquired in the as-cast CoCrNiTiV alloy, while another BCC phase together with an FCC phase and a (Ni, Co)₃Ti phase emerged through annealing. In mechanics performance, the ultimate strength significantly increases from 1729 ± 15 MPa of the as-cast alloy to 2820 ± 15 MPa of the annealed alloy, while a relatively high hardness of 825.8 ± 16.3 HV and 680 ± 23.9 HV was obtained. It was suggested that the majority BCC phase and other precipitation both take the responsibility for the good synergy in strength and hardness. (author)