Papers by Keyword: Hydrogen Absorption

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Authors: S.M.S. Nasereddini, A.A. Sheikhi Koohsar, E. Bazrafshan
Abstract: Welding-titanium and titanium alloys must be performed with special precautions because these materials are very reactive to contamination from atmosphere gases. One of the important technological considerations in welding titanium and its alloys is protection of the molten weld pool and HAZ from atmospheric gases such as nitrogen, oxygen, carbon dioxide and moisture and contamination. Absorption of the atmospheric gases affects the mechanical and metallurgical properties and may cause embrittlement, lake of fatigue strength and hydrogen cracking of titanium welds. In this paper, the effect of welding atmosphere moisture on hydrogen absorption and distribution in Ti-6Al-4V, pure titanium and TI-15V-3CR-3SN-3AL TIG welds has been studied. The experimental results indicated that hydrogen distribution which was symmetrical with respect to the weld axis had maximum and minimum points. It was also observed that heat treating the joints after welding resulted in reduction of the magnitude of the maximum and minimum points as well as redistributed the hydrogen in the welds in such a way that the distance of the maximum and minimum points got farther from the weld axis. This distribution is affected by type of titanium alloy and degree of annealing .in this investigation we used vacuum welding chamber with TIG welding apparatus and a special metal sampling and composition detecting systems for joining the samples and detecting the amount of hydrogen in the weld metal .the aim of this investigation was to increase the level of our knowledge about harmful effect of diffusion the hydrogen in the different titanium alloys. Introduction
Authors: Balázs Vehovszky, Pável Kamasa, Jozef Kováč, Zsolt Fogarassy
Abstract: Microstructural changes and relaxation processes were examined in Fe-Zr based rapidly solidified samples. These phenomena occur far below crystallization temperature in the course of heat treatment, or even at room temperature, induced by absorbed hydrogen.
Authors: Kai Sun, Zhi Qin Fan, Xiu Ying Liu
Abstract: The field-emission properties of capped(5, 5) single-walled carbon nanotubes with hydrogen adsorbed on the tip with and without an applied electric field have been investigated using first-principles density-functional theory. It is found that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions. The local density of states at the Fermi level increases with the adsorption of hydrogen molecules. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of hydrogen molecules, and are consistent with the experimental results.
Authors: Zhi Qin Fan, Rui Li, Gen Wang Cai, Jian Xing Wang, Jun De Zhang
Abstract: Using first-principles density-functional theory investigate (5, 5) capped single-walled carbon nanotubes adsorbed at one end by hydrogen molecule with and without an applied electric field. It is found that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions. The induced dipole moments is the direction of the applied electric field,and the LUMO-HOMO energy gaps decrease. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of hydrogen molecules, and are consistent with the experimental results.
Authors: Giovanni Mazzolai, A. Biscarini, B. Coluzzi, Fabio M. Mazzolai, U. Straube
Abstract: The chemical diffusion coefficient (Dc) of hydrogen in the Ni30Ti50Cu20 shape memory alloy has been determined in the temperature range 700 - 1150 K by investigating the kinetics of H2 absorption. The mobility of H has also been deduced between 250 K and 280 K from a Snoek-type internal friction peak. The values of the Einstein diffusion coefficient (DE) derived from the relaxation time of this peak were in keeping with those of Dc obtained at low H contents (nH = H/Me < 0.01 ). The combined Arrhenius plot of DE and Dc gave the following values for the diffusion parameters: W = 0.52 ± 0.02 eV, D0 = (5±2)x10-4 cm2/s.
Authors: Dorota Kocanda, Wojciech Jurczak, Ellina Lunarska, Krzysztof Swiatek
Abstract: Abstract. Paper presents the results of the studies of the service properties of the 235JR and S355J2 low alloy steels subjected to the surface modification by friction-mechanical treatment, as tested in sea water simulated solution. The resistance of steels used in the marine vessels to the wear, cavitation erosion, general corrosion, corrosion cracking and hydrogen absorption has been examined. To evaluate the effect of the surface treatment, the comparative studies of the service properties of steels before and after treatment have been considered.
Authors: Bahram Mirzaei, Goroh Itoh, Alireza Khodabandeh
Abstract: The use of duplex stainless steels (DSSs) is steadily increasing. For many uses where joining is needed, gas tungsten arc welding (GTAW) is one of the most important joining methods for DSSs. Since hydrogen embrittlement (HE) occasionally occurs in DSSs, understanding the relationship between the extent of HE and the welding condition is crucial to prevent HE. In this research, the effect of the heat input of GTAW process on the microstructure and the extent of HE in a UNS S31260 (JIS SUS329J4L) has been investigated. For this purpose, three samples have been prepared with diffrent velosity. All the samples have been cathodically hydrogen-charged, and then subjected to tensile test at a strain rate followed by fractography observation. Thermal desorption spectroscopy (TDS) has been carried out on the samples welded at low and average velosities. The results showed that tensile properties of the welded specimens were lower than those of base metal due to coarsening of the matrix ferrite grains and loss in the fraction balance of ferrite and austenite phases in the weld metal zone, where fracture took place.
Authors: Midori Yamaya, Masatoshi Futakawa, Hidefumi Date
Abstract: The mechanical properties of palladium (Pd) wire absorbed hydrogen were evaluated by the quasi-static tension test and indentation test. The electrolytic method was used for hydrogen absorption. Pd wire with a diameter of 1mm was used. The electrolyte was a sulfuric acid solution and the current density used in the electrolytic method was 200mAcm-2. The hydrogen absorption ratio defined by the molecular ratio (H/Pd) of hydrogen and palladium was controlled by the absorption time. The gauge length for the tension test was 20mm. The ultimate tensile strength increased with the increase of the absorption ratio. On the other hand, the increase of the ratio decreased the strain hardening parameter and fracture strain. A model considering the specimen absorbed hydrogen and a composite material constructed in a concentric configuration was suggested to estimate the hydrogen absorption area and mechanical properties. The indentation test was conducted to clarify the evolution of the embrittlement due to the hydrogen absorption microscopically and determine the absorption area precisely. Vickers hardness clearly increased with the increase of the hydrogen absorption ratio. The hardness distribution was measured to detect the boundary of the absorption and non-absorption area using a Berkovich indenter that is smaller than a Vickers indenter. The hardness boundary of the absorption and non-absorption of the specimen with the hydrogen absorption ratio of 22 percent was observed experimentally at the position around 100-150μm from the outside of the specimen. The position of the boundary estimated using the model was 85μm from the outside of the specimen. When the stress-strain curves of the specimen with the unknown hydrogen absorption ratio were measured, the hydrogen absorption ratio could be estimated using the proposed model.
Authors: Sergei M. Beloglazov, Georgii S. Beloglazov
Abstract: The problem under consideration concerns the prevention of absorption of hydrogen in the processes of corrosion and electroplating of all industrially used metals with the aim of the modification of chemical and physical properties of base metal surface. Its properties change towards better brightness and soldering, minimal porosity and hydrophilicity of surface, increase of hardness and wear resistance. All these properties were evaluated by means of appropriate test equipment. Residual stresses in Cr coating by phase transformation, beginning in the electroplating process, acted in combination with absorbed huge quantity of hydrogen in intrinsic defects in the steel base. Internal stresses in the base/coating region resulted in severe deterioration of the durability of steel parts, as identified by static or sign-variable fatigue tests. The new stress-step technique makes possible an analysis of H content as a function of the depth in base metals and its distribution in coating metal .
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