We proposed that the grain growth observed in electrodeposited Cu films at room temperature is caused by hydrogen-induced superabundant vacancy-hydrogen clusters. In this study, the relation between grain growth and hydrogen behavior in the electrodeposited Cu films was investigated using different types of plating baths. The Cu films were electrodeposited from an acid sulfate bath, an acid sulfate bath containing chloride ion, polyethylene glycol, and bis(3-sulfopropyl)disulfide (additive-containing bath), a pyrophosphate bath, and a chloride bath containing citric acid. Thermal desorption spectroscopy revealed that extremely high concentration of hydrogen is contained in the Cu films deposited from the additive-containing bath and the chloride bath. The room-temperature grain growth was observed in these Cu films with passage of time after deposition, concurrently with hydrogen desorption. Such grain growths were not observed in the Cu films with low hydrogen content deposited from the acid sulfate bath and the pyrophosphate bath. The changes in crystal orientation and internal stress during the grain growth of the Cu films differed between the additive-containing bath and the chloride bath. These results suggest that the room-temperature grain growth was induced by the co-deposited hydrogen in films.
The role of solute hydrogen and hydrides in the degradation of the mechanical properties of pure titanium was examined in this study. Commercially pure (99.5%) titanium was electrolytically charged with hydrogen from 50 to 2500 mass ppm and then heated in Ar at 723 K for 3 h to obtain a homogeneous solution of hydrogen. Three types of cooling process after heating were employed to obtain hydrides with different morphologies and solute hydrogen: furnace cooling and water quenching, both to room temperature, and air cooling to 473 K. The microstructures obtained with each process were coarsely precipitated hydrides or finely dispersed hydrides with dissolved hydrogen, and solute hydrogen, respectively. The ratio of the fracture strain of the hydrogen-charged specimens to that of the as-received specimen was used as an index of hydrogen degradation susceptibility (DS). The specimens having coarse hydrides showed a steep increase in DS above 600 mass ppm of absorbed hydrogen due to hydride precipitation and fracture, while the specimens with solute hydrogen showed a milder increase in DS, suggesting that solute hydrogen had a different effect on degradation. The change in DS with the strain rate of the tensile test varied for each type of specimen. The specimens with coarse hydrides showed an increase in DS in the high strain rate region due to preferred fracture of hydrides. On the other hand, DS of the specimens with solute hydrogen increased with a lower strain rate, suggesting interaction between solute hydrogen and mobile dislocations, which is also found in other metallic materials.
It is widely known that atmospheric hydrogen induces delayed fracture of high-strength steels. However, the atmospheric hydrogen behavior associated with hydrogen embrittlement has not been fully understood. In this study, using deuterium as a tracer of atmospheric hydrogen, the hydrogen behavior during deformation and fracture of SCM435 steels was studied by means of the tensile testing apparatus equipped with a quadrupole mass spectrometer installed under an ultrahigh vacuum chamber. As a result, it was revealed that the atmospheric hydrogen atoms were highly released at the beginning of plastic deformation. It was also shown that atomic hydrogen as well as molecular hydrogen was evolved at the moment of brittle fracture.
The purpose of this study is to investigate the hydrogen embrittlement property of an Al-Mg-Zn series of alloy and to propose the effective concepts to prevent the hydrogen embrittlement for automotive wheels which have shiny appearance without plating. The three types of casted an Al-Mg-Zn series of alloys in which weight fraction of Zn was 3.1, 3.4 and 4.1 mass% were prepared to discuss the effect of Zn fraction on its hydrogen embrittlement characteristics. T6 treatment was applied these alloys to improve its mechanical properties. The hydrogen embrittlement characteristics were evaluated by constant load tensile test under constant temperature. 1 mass% of NaCl solution was dropped to notch of the specimen to evaluate the time until fracture under controlled corrosive environment. Hydrogen generation under corrosive environment and microscopic segregations of materials were also evaluated. Test results were as follows: The rate of diminution in tensile strength at corrosive environment was increased with the increase of the weight fraction of Zn. Microscopic observation showed that the hydrogen generation was active at around the segregation and the number of segregations was increased with the increase of the weight fraction of Zn. According to these results, a reduction in the number and size of segregation is an effective way to prevent hydrogen embrittlement.
The development of low-Mo austenitic stainless steels for high-pressure hydrogen valves and joints was undertaken to contribute to resource saving. Low-strain-rate tensile tests were carried out at 233 K in 70 MPa high-pressure gaseous hydrogen. The fracture surfaces of specimens tested in high-pressure gaseous hydrogen were observed by scanning electron microscopy. The effect of hydrogen charging on room-temperature creep deformation was studied. The resistance of the specimens to hydrogen gas embrittlement was revealed by the results of the low-strain-rate tensile tests. Specimens that fractured in gaseous hydrogen at 70 MPa in 233 K underwent shear deformation rather than cup-and-cone deformation. A small difference in the creep deformation was recognized between hydrogen-charged and uncharged specimens.
The variation of the niobium (Nb) oxide catalyst during hydrogen absorption and desorption reactions was investigated by in-situ X-ray absorption spectroscopy (XAS). Results indicated that H2 was easily dissociated on the catalyst because the hydrogen absorption kinetics was significantly improved, and then the hydrogen atoms were diffused through inside of the catalyst. Thus, the catalytic mechanism of Nb oxides is different from that of conventional metal catalysts, in which the dissociated H is moved on the surface of catalyst.
Compositional dependence of hydrogenation properties in Ti1+y(Fe1−xMnx)1−y were investigated. The annealed alloys mainly showed B2 structure (CsCl) and some of them contained a small amount of secondary phase. The lattice constant of B2 phase increased and their equilibrium pressures decreased with increasing Mn or Ti content. Ti50Fe40Mn10 and Ti50Fe35Mn15 showed two distinct flat plateaus on pressure-composition isotherms. Ti52Fe28Mn20 and Ti53Fe25Mn22 also showed two distinct flat plateaus below certain temperatures. Above those temperatures, however, only their first plateau became slant without hysteresis keeping the second plateau flat. In addition, the first plateau was slanted without hysteresis even at room temperature in Ti54Fe23Mn23. These results suggest that Ti1+y(Fe1−xMnx)1−y have critical temperatures for the first phase transformation from the α-solid solution phase to the β-Ti1+y(Fe1−xMnx)1−yH~1 and they decreased with increasing Mn or Ti content.
We introduce the spectroscopic investigation of the nano-composite materials consisted of Mg and Pd. Mg is most promising material for the application of the hydrogen storage because of the high gravimetric hydrogen storage capacity up to 7.6 mass%. In spite of the advantage of the hydrogen storage capacity, the practical use of Mg has not been established due to the slow hydro-/dehydrogenation reactions and the high temperature required to store and release the hydrogen. Nano-sized Mg such as Mg nanoparticle is expected to store the hydrogen rapidly because of the high specific surface area of the nanoparticle. Moreover, addition of Pd decreases the temperature for the hydrogen storage of Mg because of the catalytic effect for the dissociation reaction of hydrogen molecules. We have fabricated the nanoparticles composed of the both Mg and Pd by the gas evaporation method using He gas. These nanoparticles can store the hydrogen at the room temperature. After the storage of the hydrogen, the release of the hydrogen has not been observed up to 100℃. The analyses of the X-ray absorption fine structure (XAFS) have revealed that the irreversible change of the chemical state during the hydrogen storage causes the inactivation of the surface of nanoparticles and inhibits the dehydrogenation reaction of the MgH2.
Structural changes on hydrogen absorption process of hydrogen absorbing alloy LaNi4.75Sn0.25 have been investigated by time-resolved X-ray diffraction measurements using synchrotron radiation source. We have found the transient intermediate phase between the solid solution and hydride phases of LaNi4.75Sn0.25 under non-equilibrium hydrogen pressure condition at room temperature. LaNi4.75Sn0.25 has transformed into the hydride through three phase co-existing state. The hydrogen content of the intermediate phase estimated from the unit cell volume is independent of the induced hydrogen gas pressure. The variation of lattice constants indicate that the hydrogen atoms are located at the La2Ni2(Ni, Sn)2 octahedron and La2(Ni, Sn)2 tetrahedron in the intermediate phase.
The effect of a quenching rate on the hydrogen storage properties of V0.79Ti0.2Zr0.01 was investigated. Two V0.79Ti0.2Zr0.01 samples with different quenching rates were prepared; one was quenched from 1673 K to the ice-water temperature in less than 1 s (V0.79Ti0.2Zr0.01-FQ) and the other was quenched more slowly (V0.79Ti0.2Zr0.01-SQ). Both samples are single phase and no notable difference in their average structure was found. Pressure-composition isotherm curves representing transition between monohydride and dihydride phases at 410 K show that V0.79Ti0.2Zr0.01-FQ absorbs hydrogen at much higher pressure than V0.79Ti0.2Zr0.01-SQ. In addition, V0.79Ti0.2Zr0.01-FQ has a more slanting absorption plateau. During 15 hydrogen absorption and desorption cycles, gradual reduction in hydrogen absorption plateau pressure was observed only in V0.79Ti0.2Zr0.01-FQ. Our preliminary local structural study using the atomic pair distribution function analysis show that their structural correlations start to deviate around 5.5 nm.
Behavior of hydrogen in a tensile-deformed Al-9 mass%Mg alloy was investigated by means of hydrogen microprint technique, HMPT, a method to visualize the microscopic location of hydrogen emission from specimen surface as silver particles. Hydrogen emission was observed on some of grain boundaries. The amount of surface relief and the maximum gradient across the grain boundary with hydrogen emission were larger than those without hydrogen emission. Most grain boundaries with hydrogen emission were from 61 to 75 degree to tensile direction and nearly parallel to slip lines. The results suggest that slip deformation parallel to and close to grain boundary plane caused hydrogen transport with moving dislocations to the surface, breakage of the surface oxide film on the grain boundary, and then the emission of the hydrogen atoms.
In this study, the effect of the surface structure and hydrogen on the fatigue strength of electroless Ni-P plated Al-2%Cu and Al-2%Zn alloys was investigated. As the results, the following points were clarified. (1) Large precipitates (size) were recognized near the specimen surface of the furnace-cooled Al-Cu alloy, but these were not recognized in the furnace-cooled Al-Zn alloy. (2) Fatigue strength of the Al-Cu alloy specimen subjected to Ni-P plating after a furnace cooling treatment was overall reduced rather than one of the non-processed specimens. (3) Fatigue strength of the Al-Zn alloy specimen subjected to Ni-P plating after the furnace cooling treatment showed a clear increase in comparison to one of non-processed materials. (4) In both the Al-2%Cu and Al-2%Zn alloy specimens subjected to Ni-P plating after the furnace cooling treatment, a clear hydrogen desorption was recognized. On the other hand, there was only hydrogen desorption from a few of the non-processed specimens. It is considered that the poor fatigue strength of the plating materials is mainly due to the interaction between the surface precipitates and hydrogen gas.
In this study, the effect of electroless Ni-P plating on the mechanical properties of Al-4%Ge alloy was investigated. As the results, the following points were clarified. (1) Tensile strength of the specimen subjected to the Ni-P plating after aging treatment or furnace cooling treatment was improved by about 10% in comparison to one of the non-processed specimens. (2) Breaking elongation of the specimen subjected to the Ni-P plating after aging treatment showed no significant changes in comparison to one of the non-processed specimens. On the other hand, breaking elongation of the specimen subjected to Ni-P plating after a furnace cooling treatment was reduced to 70% in comparison to one of the non-processed specimens. (3) Fatigue strength of the specimen subjected to the Ni-P plating after a furnace cooling treatment was overall reduced rather than one of non-processed specimens. (4) Fatigue strength of the specimen subjected to the Ni-P plating after aging treatment was overall reduced, except for the low-stress region, rather than one of the non-processed specimens. (5) In the specimen subjected to Ni-P plating after a furnace cooling treatment or aging treatment, clear hydrogen desorption was recognized. On the other hand, there was only hydrogen desorption from a few of the non-processed specimens. Especially, it is considered that the poor fatigue strength and ductility of the plating materials are mainly due to the interaction between the surface precipitates and hydrogen gas.
In this study, we examined the influence of surface precipitates and hydrogen gas on the fatigue strength of an electroless Ni-P plated Al-1.2%Si alloy. As the results, the following points were clarified. (1) Fatigue strength of the specimen subjected to zincate treatment only after a furnace cooling treatment was almost the same as only furnace cooling. (2) Fatigue strength of the specimen subjected to Ni-P plating after a furnace cooling treatment was reduced overall, except for the high-stress region, rather than one of the non-processed materials. (3) Fatigue strength of the specimen subjected to Ni-P plating after aging treatment showed a clear increase in comparison to one of the non-processed materials. (4) In the specimens subjected to the Ni-P plating after a furnace cooling treatment or aging treatment, clear hydrogen desorption was recognized. On the other hand, there was only hydrogen desorption from a few of the specimens subjected to zincate treatment after the furnace cooling treatment or only furnace cooling. It is considered that the poor fatigue strengths of the plating materials are mainly due to the interaction between the surface precipitates and hydrogen gas.