Increasing Charging Time Research Articles

Hydrogen evolution from cathodically charged Ti3Al-based titanium aluminium alloy

Abstract A single-phase Ti3Al-based titanium aluminium alloy, Ti–25Al, was cathodically charged with hydrogen in a 5% H2SO4 aqueous solution for charging times up to 43.2 ks, and the formation and dissociation of a hydride, hydrogen evolution behavior and total hydrogen uptake were investigated by means of X-ray diffractometry and thermal desorption spectroscopy (TDS). After cathodic hydrogen charging, hydrogen concentrated mainly at the surface of the sample as a hydride phase, whose crystal structure probably is of a hexagonal type with the lattice parameters of a=0.60 nm, c=0.47 nm. Hydrogen also induced cracks and pits at grain boundaries or within grains. Three kinds of TDS peak, for which one corresponded to the hydride dissociation and the others presumably corresponded to trapping of hydrogen, could be found after longer hydrogen charging. The apparent hydrogen uptake in the Ti–25Al alloy increased with increasing charging time and the uptake level after charging for 43.2 ks was estimated to be about 700 wppm.

工業用純チタンの水素化物形成挙動に及ぼす窒素イオン注入の影響

A commercially supplied pure titanium was ion-implanted at 1.5 MeV with different doses of N2+ ranging from 5×1020 to 2×1021 ions per 1 m2, and the titanium hydride formation behavior was investigated in 10 mass% sulphuric acid aqueous solutions.When the implantation dose is larger than 1×1021 ions per 1 m2, the titanium nitride is detected on the implanted surface by the atomic force microscope(AFM) and X-ray diffraction(XRD). According to the XRD analysis of the unimplanted specimen hydrogen-charged at a constant current density of 500 A/m2, the amount of hydride increases with increasing charging time and the whole surface is covered by hydride when the charging time is 12 ks. For all of the implanted specimens, on the other hand, the amount of hydride is less than that for the unimplanted specimens within the charging time of 12 ks. The amount of hydride on the specimen implanted with 1×1021 ions per 1 m2 is a little larger than those implanted with 5×1020 and 2×1021 ions per 1 m2. The observation by AFM supports the results of XRD analysis.

Hydride formation in two-phase ( Ti3Al + TiAl) titanium aluminides during cathodic charging and its dissociation

A (TiAl)H x hydride which has a tetragonal crystal structure with lattice parameters a = 0.452 nm and c = 0.326 nm ( c/ a = 0.721) has been observed in Ti42Al, Ti45Al and Ti50Al (at.%) two-phase (Ti 3Al ( α 2) + TiAl ( γ)) titanium aluminides by cathodic charging in a 5% H 2SO 4 solution. Cracks or pits are also observed within the γ phase regions in the two-phase ( α 2 + γ) coexisting grains (such as lamellar grains) but not within the α 2 phase or single γ grains. Weights of the samples decrease with increasing charging time owing to the crack or pit formation, and this is more drastic in the Ti—50Al alloy than in the Ti—42Al and Ti—45Al alloys. The hydride is thermally stable at temperatures up to about 550 K (277 °C) and dissociates completely at temperatures between 673 K (400 °C) and 723 K (450 °C).

An anomaly of positron parameter appearing in the study of an electron brush-plated material — Is it possible to use positron to detect molecular hydrogen content?

On account of the ease with which positron annihilation experiments may be made and the well-known manner in which positrons behave much in the way that hydrogen protons do, the positron technique is thus commonly used to study hydrogen-charging and hydrogen-absorbed metals and alloys. Indeed, the positron technique has been an indispensable and powerful tool to investigate the influence of hydrogen on microstructures and properties of materials, thus a lot of the related papers have been published. However, papers regarding the use of positrons to detect molecular hydrogen content are few in the literature. This is because hydrogen-charging of metallic materials is a quite complicated process. Generally speaking, when hydrogen-charging, the content of hydrogen increases but occasionally it becomes lower instead of higher with increasing charging time. In addition, positrons, after entering a material, are affected not only by the old defects and the newly generated defects, but by hydrogen proton screening as well. Therefore, the existence of certain relationships between the measured positron parameter and hydrogen content in the material has not been found. Among the curves of positron parameter as a function of charging time which appeared in publications, the one which has a wavelike characteristic was frequentlymore » seen. In this letter, the author found that the measured Doppler lineshape parameter happens to be roughly directly proportional to the molecular hydrogen content involved in a particular material.« less

高力アルミニウム合金の応力腐食割れにおける水素脆性関与のモデル実験

Hydrogen embrittlement and SCC behavior of bending 7075-T6 aluminum alloy specimens were examined. The compression side of each specimen with both side notchs was only exposed to the cathodic charging solution or SCC environment. The notch strength was gradually decreased with increasing charging time. Prominent embrittlement was found on the tension side, but not on the compression side. Both the embrittlement and cracking on the tension side were also found in a SCC test specimen of which the compression side was only exposed. These results were only caused by the understood by the mechanism of hydrogen embrittlement hydrogen permeated from the compression side and transported to the tension side by diffusion. Thus, it was concluded that the hydrogen embrittlement was involved in the SCC mechanism.

Simulation of Blister Growth in Hydrogen-Induced Cracking of Rolled Pure Iron.

The commercially supplied pure iron which was rolled to various reductions was cathodically hydrogen-charged in sulfuric acid solution to investigate the blister growth behavior in hydrogen-induced cracking. In addition, a computer simulation was carried out to predict the blister growth characteristics. The experimental result showed that the diameter of blisters increased with increasing charging time and rolling reduction. By assuming an increase in dislocation density (hydrogen trapping site) and an increase in growth rate of blister with increasing rolling reduction, the computer simulation could well predict the blister growth process and the three-dimensional distribution of blisters inside the material.

α+β型Ti-6Al-4V合金の水素化物の析出挙動

The behavior of hydrogen absorption and hydride precipitation has been studied on a Ti-6Al-4V alloy cathodically charged at various current densities using X-ray diffraction analysis, internal friction measurement and transmission electron microscopy.The 200 spacing and considerable X-ray line broadening of β phase increased with increasing cathodic charging time. The α phase, however, was not significantly affected by the cathodic charging.A relaxation peak relating to the hydrogen atoms in the β phase was observed in the internal friction versus temperature curve. The increase in the peak height corresponded to the increase in the 200 spacing of β phase in the X-ray line profile.Hydrogen atoms in the β phase were detected by both the internal friction measurement and X-ray diffraction analysis. It was observed that the hydrides mainly precipitated at the α/β interface for cathodic charging of the low current density, but precipitated in both the α phase and the β phase for the high current density.The precipitation amount of hydrides estimated from the X-ray line profile and the peak height at 190-220 K in the internal friction versus temperature curve increased with increasing charging time for the high current density. Consequently, the peak was considered to be related to the hydrides. The hydrides were detected by internal friction, though it was difficult to detect the hydrides by using X-ray diffraction analysis for the low current density.