We have operated a 4 V-class bulk-type, all-solid-state LiCoO2/Li battery at room temperature. The composition consisted of a Li4(BH4)3I complex hydride electrolyte for the electrolyte layer, and a 80Li2S 20P2S5 sulfide glass for an electrolyte in the positive electrode layer. The battery assembled exhibited a 92 mAh•g−1 initial discharge capacity at 298 K and 0.1 C. The discharge capacity for the 20th cycle remained as high as 83 mAh•g−1, corresponding to a capacity retention ratio of nearly 90%.
Behavior of hydrogen in a tensile-deformed Al-Zn-Mg alloy was investigated by means of hydrogen microprint technique, HMPT, which is a method to visualize location of hydrogen emission from the surface as silver particles. Hydrogen was introduced into the test pieces from one side by cathodic electrolytic charging for 30 min. Then, the test pieces were stretched with continuing the charging, followed by HMPT observation on the other side. Hydrogen evolution was observed on some grain boundaries where the surface relief was formed. Discussion was made considering preferential plastic deformation in precipitate free zones, PFZs, and the geometrical relationship of the boundaries with tensile axis and with slip band inside grains. The results indicated that the shear deformation along grain boundary caused transportation of hydrogen atoms with gliding dislocations to the surface, breakage of surface oxide film, formation of surface relief and then the emission of hydrogen atoms. It was suggested that the preferential deformation in the precipitate free zone was attributed to hydrogen evolution.
The hydrogen embrittlement of the SK85 high strength steel sheet was evaluated by three-point bending test, and the effect of zinc electroplating and zinc-nickel alloy electroplating on the hydrogen brittleness of steel was examined by this method. It was found that the evaluation of hydrogen brittleness for the high strength steel sheet by three-point bending test was possible to obtain the effective result. Zinc electroplating made hydrogen brittleness promote by the hydrogen based on the reduction of hydrogen ion during the electroplating, because zinc plating acted as a barrier film for hydrogen evolution from the substrate. The hydrogen brittleness of zinc-nickel alloy electroplating was suppressed in comparison with that of zinc plating. It seems that large number of cracks in a film enable the hydrogen diffusion.
The influence of co-deposited hydrogen on the room-temperature grain growth of electrodeposited Cu films was investigated. The films were prepared from ethylenediamine (EDA)-complex and ethylenediaminetetraacetic acid (EDTA)-complex baths and examined with respect to hydrogen concentration, the initial microstructure, residual stress and impurities. Thermal desorption spectroscopy revealed that extremely high concentrations of hydrogen was contained in the Cu films deposited from both the EDA- and EDTA-complex baths. The room-temperature grain growth of these Cu films proceeded after deposition and concurrently with the gradual desorption of hydrogen. During the grain growth, the (111)-oriented texture remained almost unchanged but the tensile stress decreased. Compared with the Cu films electrodeposited from other types of baths, temporal changes in crystal orientation and residual stress varied in the different baths, however grain growth proceeded with a decrease in hydrogen as previous. These results indicate that the primary cause of room-temperature grain growth of electrodeposited Cu films is hydrogen-induced superabundant vacancies.
Although Mg based hydrogen storage materials absorb hydrogen immediately under appropriate thermodynamic conditions, an obvious incubation period exists for hydrogen desorption. This fact implies that the mechanisms of hydrogen absorption and desorption are different from each other. During hydrogen desorption process, nucleation and growth of Mg are occurring in MgH2. It is considered that free surface is the only nucleation site of Mg in hydrogen desorption process. The nucleation frequency per unit specific surface area should be constant under a fixed temperature and H2 partial pressure. Therefore, it is estimated that the incubation period is proportional to the inverse of specific surface area. The relationship between incubation period and specific surface area of MgH2 was investigated in order to understand the mechanism of incubation period on magnesium-hydrogen system. MgH2 with several kinds of specific surface area were manufactured by changing milling time of a planetary ball mill. A primary Gibbs free energy for dehydrogenation was conducted as −1.94 kJ mol−1 by controlling H2 pressure for measuring incubation period. The results revealed that the incubation period was proportional to the inverse of specific surface area.
The 7000 series alloys have the highest strength in the aluminum alloys, but lower fatigue properties than 2000 series alloys. Thus, 7000 series alloys are not applied to a large proportion of the aircraft components. However, the mechanism for this has not been elucidated yet. In humid air, hydrogen embrittlement based on intergranular cracking has been known to occur in 7000 series alloys. In order to explain the difference in the fatigue crack growth behavior in the two series alloys, the effect of the test environment on the fatigue crack growth of the two series alloys has been investigated in this study. Alloys of 7075- and 2024-types with relatively coarse equi-axed grains were T6- and T4-tempered, respectively, and subjected to fatigue crack growth test in humid and dry environments. Crack growth rate at low ΔK levels was clearly larger in 7075-type alloy than 2024-type alloy, in the humid air. In order to investigate this result more in detail, the two alloys were subjected to slow strain rate tensile test in the two environments to evaluate their sensitivity to hydrogen embrittlement. The sensitivity of 7075-type alloy was higher than 2024-type alloy. From this result together with fractography study, the larger fatigue crack growth rate of the 7075-type alloy is attributable to hydrogen embrittlement.
Mg is hydrogenated as core-shell type hydride in which the surface is covered with MgH2 (shell) and unreacted Mg remains at the internal side (core). Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials, although several treatments were proposed to enhance their absorption capacity. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH2 in Mg were investigated using pure Mg and Mg-(3-9)mass%Al-1 mass%Zn alloys (AZ). MgH2 was formed on the surface as well as inside of unreacted Mg core which was apart from both gaseous H2 and the surface MgH2 layer. The inside MgH2 was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH2 and size of the internal MgH2 increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH2. However, the growth of the surface and internal MgH2 came to a halt after the surface was covered with MgH2. The increase in Al concertation in AZ lead to decrease in thickness of the surface MgH2, prolongation of the halt time and increase in the internal MgH2 grain size. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH2 because diffusion rate of H in Mg was much higher than that in MgH2. In addition, the growth of internal MgH2 as well as control of surface MgH2 can contribute to the promotion of the complete hydrogenation of Mg based hydrogen storage materials.
A procedure for the control of the excess energy of Ni thin-film formation by the ion-plating process has been studied. The excess energy of metal vapor particles is dependent not only on the kinetic energy of metal vapor ions but also on the ionization rate as the impinging rate of the ions on the substrate. A hot-filament electron emitter was used to increase the ionization rate. Ni thin films were prepared using the ion-plating process with a hot-filament electron emitter. The excess energy introduced during the Ni thin film formation was determined by plasma diagnostics using the Langmuir probe, Faraday cup, and a multigrid analyzer (MGA) as an ion energy analyzer. The ionization rate of Ni particles (ZNi+/ZNi) increased with electrons emission. The hot-filament electron emitter is effective in increasing the excess energy. Internal stresses in the Ni thin film were tensile in all samples. Tensile stress decreased with increasing ionization rate. Ion bombardment resulted in the enhancement of the compressive stress possibly because of the ion-pinning effect.
In recent years, metallic biomaterial applications have demanded a relatively low elastic modulus of around 30 GPa that is nearly equal to that of bone. However, in the case of spinal fixture applications, metallic materials with a relatively high Young's modulus are required to suppress spring -back by elastic and plastic deformation during implantation. Therefore, Young's modulus control by stress-induced transformation in a newly developed biomedical β-type Ti-12Cr alloy, has been proposed by the present authors. However, the relationship between the microstructure and mechanical properties of Ti-12Cr has not been fully investigated up till now. Therefore, changes in the mechanical properties of Ti-12Cr were investigated through heat treatment and the fine particle bombarding process (FPB), which is a surface modification process used in this study. Peak aging of Ti-12Cr heated at 673 K showed for around 2.4 ks. The Vickers hardness of Ti-12Cr in the peak aging condition (PA) at 673 K was around 90% (HV 524) higher than that (HV 294) in the solutionized condition (ST). Meanwhile, both the 0.2% proof stress and tensile strength of Ti-12Cr in the PA at 673 K were also around 50% higher those in the ST. However, the ductility of Ti-12Cr in the PA at each temperature reduced significantly. Therefore, a solo-solution treatment was judged to be the optimal heat treatment for Ti-12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young's modulus of as-solutionized Ti-12Cr subjected to FPB increased by around 40% and 70%, respectively, at the very edge of the specimen surface, as compared to those of the unprocessed sample. Furthermore, the fatigue strength of Ti-12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti-12Cr rose slightly with an increase in the implantation period from 24 to 52 weeks.
Recently, AM (Additive Manufacturing) process which can produce highly complex components have been gaining significant attention in both industry and academic research. Numerous metals and alloys have been processed by selective laser melting; Ti alloys, Ni alloys, and Co-Cr alloys have been the subjects of recent work. Ni-based superalloys have precipitated phases such as γ′ and γ″ phase and Ti alloys and Co-Cr alloys are the multiphase alloys which have phase transformation, thus it is difficult to clarify the influential factors of AM process on strengths of these alloys. In this study, we used SUS316L stainless steel which is a single-phase solid-solution alloy and does not have precipitated phase in order to clarify characteristic influential factors of AM compared with a conventional material. SUS316L was fabricated by selective laser melting by ytterbium fiber laser from fine metallic powder. It was found that the coarse columnar grains grew up along the built direction and the columnar cell structure of dislocations which are induced during the AM process. During the solution heat treatment, the dislocation recovery was observed. AM specimens showed higher tensile and creep strengths compared with the conventional (hot working) material because of the high-density of dislocations. Ductility of AM specimens was lower than the conventional material because of defects due to lack of fusion at molten pool boundaries; furthermore, the specimens whose loading direction corresponds to built direction showed lower strength and elongation than the specimens whose loading direction perpendicular to built direction due to the oriented defects.