scholarly journals Anisotropy of hydrogen diffusion in nickel single crystals: the effects of self-stress and hydrogen concentration on diffusion

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
J. Li ◽  
A. Oudriss ◽  
A. Metsue ◽  
J. Bouhattate ◽  
X. Feaugas
Keyword(s):  
Single Crystals ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion

Investigation of Hydrogen Diffusion Characteristics of the Heat Affected Zone of 2.25Cr-1Mo-0.25V Steel by an Electrochemical Permeation Method

2019 ◽  
Author(s):  
Xin Song ◽  
Zelin Han ◽  
Bin Liu ◽  
Mu Qin ◽  
Yuancai Duo ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Hydrogen Concentration ◽  
Heat Affected Zone ◽  
Hydrogen Diffusion ◽  
Trap Density ◽  
Hydrogen Diffusivity ◽  
Hydrogen Flux ◽  
Hydrogen Trap ◽  
Diffusion Characteristics ◽  
Effective Hydrogen

Abstract The heat affected zone (HAZ) of 2.25Cr-1Mo-0.25V welded joint is a critical part for the safety of hydrogenation reactors. Hydrogen has a significant effect on the HAZ, studying hydrogen diffusion characteristics, such as: hydrogen flux and the effective hydrogen diffusivity has a remarkable value in investigating the hydrogen-induced material degradation mechanisms. In this work, an electrochemical permeation method was applied to study the hydrogen diffusion characteristics of HAZ. Then, the metallographic microscope and a software “Image J” were used to analyze the density of grain boundaries of HAZ. The effect of the post–weld heat treatment (PWHT, i.e. annealing) on the hydrogen diffusion characteristics of HAZ was also been investigated. The results show that after PWHT, the effective hydrogen diffusivity of HAZ increases from 1.63 × 10−7cm2·s−1 to 3.68 × 10−7cm2·s−1, the hydrogen concentration decreases from 1.92 × 10−4mol·cm−3 to 1.09 × 10−4mol·cm−3, and the hydrogen trap density decreases from 3.00 × 1026m−3 to 0.76 × 1026m−3. Thus, PWHT can significantly reduce density of grain boundaries, thereby reducing the hydrogen trap density, enhancing the hydrogen diffusivity and reducing the hydrogen concentration.

Hydrogen Diffusion in Chalcopyrite Solar Cell Materials

1998 ◽  
Vol 513 ◽  
Author(s):  
A. Weidinger ◽  
J. Krauser ◽  
Th. Riedle ◽  
R. Klenk ◽  
M. Ch. Lux-Steiner ◽  
...  
Keyword(s):  
Thin Films ◽  
Solar Cell ◽  
Grain Boundaries ◽  
Single Crystals ◽  
Diffusion Coefficients ◽  
Transport Process ◽  
Hydrogen Diffusion ◽  
Intrinsic Diffusion ◽  
Ion Energy ◽  
Temperature Range

ABSTRACTHydrogen diffusion in CuInSe 2 single crystals and CuInS2 thin films was studied by measuring the spreading of implantation profiles upon annealing. Deep implantation with an ion energy of 10 keV and sub-surface implantation with 300 eV were applied. The diffusion coefficients in both materials were found to be in the order of 10-14 to 10-13 cm2/s in the temperature range between 400 and 520 K.These fairly low diffusivities are typical for a trap and release transport process rather than intrinsic diffusion of interstitial hydrogen. In the polycrystalline CuInS2 films, hydrogen leaves the sample through the grain boundaries.

Electromagnetic Induction Post Heating to Reduce NDE Delay Times of Welding In-Service Repairs

2020 ◽  
Author(s):  
Liam Hagel ◽  
Jonathan Prescott ◽  
Alireza Kohandehghan ◽  
Stuart Guest ◽  
Sean Lepine
Keyword(s):  
Stress Concentration ◽  
Hydrogen Concentration ◽  
Induction Heating ◽  
Thermal Convection ◽  
Heat Affected Zone ◽  
Hydrogen Diffusion ◽  
Heat Removal ◽  
High Energy ◽  
Fillet Weld ◽  
Delay Times

Abstract When a pipeline requires a repair, a pressure-containing steel sleeve or an emergency repair fitting is often fillet welded to the in-service pipe to return the pipeline to normal service conditions. During welding, the flowing product rapidly quenches the fillet weld, promoting the formation of high hardness and low ductility microstructures in the heat-affected zone. The rapid cooling rates also limit the mobility of diffusible hydrogen introduced from the welding electrodes. The hydrogen can be trapped in the weld metal and heat-affected zone and concentrated in specific locations throughout the weld based on the welding deposition sequence. Fillet welds also contain inherent locations of geometric stress concentration at the weld toes and root locations. The elevated hydrogen concentration in the in-service weld, combined with the geometrical stress concentrations at the location of crack-susceptible microstructures, can increase the likelihood of forming a hydrogen-induced crack. Delayed non-destructive examination (NDE) is often employed to wait a sufficient time for any cracks to form so they can be detected. To reduce hydrogen concentration at the locations of stress concentration and NDE delay times, post-heating can be applied to the in-service weld. Elevating the temperature within the weld can enable hydrogen diffusion and reducing the cracking propensity. The rapid heat removal due to flowing product requires post-heating techniques with high energy outputs that will not overheat the steel surfaces. Electromagnetic induced current (induction heating) methods can produce sufficient thermal energy in the electrically conductive steel pipe and sleeve. Coupled numerical finite element analysis (FEA) models were utilized to simulate various induction cable arrangements and thermal convection coefficients, representative of various pipeline products. The analysis of the induction heating arrangements for the studied thermal convection coefficient was conducted to achieve a minimum temperature of 120 °C in the fillet weld root and toes to enable sufficient thermal driving force for hydrogen diffusion while ensuring the pipe and sleeve surface temperature does not exceed 200 °C. An optimal induction heating procedure was found to which could achieve the target temperatures within a reasonable heating time such that NDE delay times of in-service welds can be reduced by 5–6 times.

Diffusion of Hydrogen in Titanium-Vanadium Alloys

2005 ◽  
Vol 237-240 ◽  
pp. 340-345 ◽  
Author(s):  
Hans Jürgen Christ ◽  
S. Schroers ◽  
F.H.S. dos Santos
Keyword(s):  
Diffusion Coefficient ◽  
Titanium Alloys ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
High Strength ◽  
Vanadium Concentration ◽  
Vanadium Alloys ◽  
High Hydrogen ◽  
Hydrogen Diffusion Coefficient ◽  
Diffusion Of Hydrogen

β–titanium alloys are very attractive materials for many applications because they combine low density, high strength and excellent corrosion resistance. The available data indicate a much higher hydrogen diffusion coefficient in β–titanium alloys as compared to α and α + β alloys. In order to predict the range of applicability of β–titanium alloys in environments, which release hydrogen, the hydrogen diffusion coefficient (DH) needs to be known quantitatively. In the framework of this study the value of DH was determinated on samples, which were electrochemically hydrogen charged. Long thin rods were used as samples and charged in such a way that high hydrogen concentrations were obtained in one half of the length of the specimens, while the other half was kept virtually unaffected. After charging, the rods were annealed enabling hydrogen to diffuse. Hydrogen concentration profiles were experimentally determined and evaluated on the basis of the Matano technique, in order to reveal any effect of concentration on DH. The experiments were carried out on β–titanium alloys of the binary Ti–V system. The concentration range of vanadium in the alloys studied was selected in such a way that it represents the compositions commonly found in commercial alloys. The results show that the effect of hydrogen concentration on DH is negligible and that DH increases with the vanadium concentration.

Kinetic Monte Carlo Simulation of Hydrogen Diffusion in Tungsten

2016 ◽  
Author(s):  
Xue Yang ◽  
Wasiu O. Oyeniyi
Keyword(s):  
Monte Carlo ◽  
Hydrogen Concentration ◽  
Diffusion Coefficients ◽  
Hydrogen Diffusion ◽  
Kinetic Monte Carlo ◽  
Bcc Lattice ◽  
Tetrahedral Sites ◽  
Calculation Results ◽  
Diffusion Paths ◽  
Lattice Surface

This research developed a Kinetic Monte Carlo (KMC) method for simulating hydrogen diffusion in tungsten bulk. The KMC inputs such as diffusion paths and energy barriers are taken from DFT calculation results from the literatures. In this simulation model, stable hydrogen interstitial sites in tungsten are the tetrahedral sites on each surface of the bcc lattice, and each site has four tetrahedral neighboring sites, with two neighbors on the same lattice surface and the other two on the adjacent two perpendicular surfaces. A MATLAB script has been developed to perform the diffusion modeling for any given hydrogen concentration and substrate temperature. To compare the simulation results with experiment measurements, modeling configuration of low hydrogen concentration and temperature of 300 K to 2500 K mirroring the experiment conditions was used. The calculated diffusion coefficients at various temperatures match the experiment reference very well. The calculated diffusion coefficients are also fitted to the Arrhenius equation as: D [m2/s] = 5.59×10−7 exp(−0.426/kBT)

Anisotropy of Hydrogen Diffusivity in ZnO

2013 ◽  
Vol 333 ◽  
pp. 39-49 ◽  
Author(s):  
Jakub Čížek ◽  
František Lukáč ◽  
Marián Vlček ◽  
Martin Vlach ◽  
Ivan Procházka ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
Surface Region ◽  
Nuclear Reaction Analysis ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
Slow Positron ◽  
X Ray

Hydrogen absorption and diffusivity in high quality ZnO crystals were investigated in this work by X-ray diffraction combined with slow positron implantation spectroscopy and electrical resistometry. ZnO crystals were covered by a thin Pd over-layer and electrochemically charged with hydrogen. It was found that absorbed hydrogen causes plastic deformation in a sub-surface region. The depth profile of hydrogen concentration introduced into the crystal was determined by nuclear reaction analysis. Enhanced hydrogen concentration was found in the sub-surface region due to excess hydrogen atoms trapped at defects introduced by plastic deformation. Hydrogen diffusion in ZnO crystals with various orientations was studied by in-situ electrical resistometry. It was found that hydrogen diffusion in the c-direction is faster than hydrogen diffusion in the a-direction most probably due to open channels existing in the wurtzite structure along the c-axis.

Comparison of Decoupled and Coupled Analyses for Hydrogen Transport in Fracture Specimens

2007 ◽  
Author(s):  
Y. Kim ◽  
Y. J. Chao ◽  
M. J. Morgan ◽  
P.-S. Lam
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
Constitutive Models ◽  
Coupled Model ◽  
Hydrogen Transport ◽  
Blunt Crack ◽  
The Difference ◽  
Point Bend ◽  
Fracture Specimens

Hydrogen embrittlement is an important issue in many industries. Fracture resistance of metals is often weakened by the presence of hydrogen. In this paper, two diffusion models are compared for hydrogen transport analysis. One is the coupled model where the concentration of hydrogen in the lattice is integrated with mechanical properties. The other is the decoupled model in which the hydrogen diffusion is independent of the mechanical properties; but depends on the stress state. Finite element analyses are performed for a boundary layer specimen with a blunting crack and a four-point bend specimen with rounded notch. Hydrogen concentration profiles around the blunt crack (or notch) are compared under different boundary conditions and material properties. It is observed that, in spite of the difference in constitutive models, there is a similarity between hydrogen concentration in normal interstitial sites by the two models. In case that large plastic strain is present (such as those in low to moderate strength steels) there is a substantial difference in hydrogen concentration between the two models.

The Analysis of Hydrogen Diffusion Behaviors Coupled With the Analysis of Heat Transfer Around the Heat Affected Zone of Welding

2014 ◽  
Author(s):  
Toshihito Ohmi ◽  
Toshimitsu Yokobori ◽  
Kenichi Takei ◽  
Yuki Konishi
Keyword(s):  
Heat Transfer ◽  
Heat Treatment ◽  
Residual Stress ◽  
Hydrogen Embrittlement ◽  
Stress Field ◽  
Hydrogen Concentration ◽  
Incubation Time ◽  
Hydrogen Diffusion ◽  
Local Stress ◽  
Weld Heat

Hydrogen penetrates into the metal and causes Hydrogen embrittlement due to the increase in hydrogen concentration. This is caused by the local stress fields such as residual stress field at the site of welding or local stress field around a crack tip. It accompanied with incubation time of several hours since the components were exposed to hydrogen atmospheric condition. This incubation time is time lag of hydrogen diffusion and concentration at the site where the hydrogen embrittlement occurs. Therefore, clarification of the hydrogen diffusion behavior is important to prevent from fracture of hydrogen embrittlement. In this paper, the numerical analyses of hydrogen diffusion around weld part including HAZ (Heat Affected Zone) under residual stress coupled with that of heat transfer during the cooling process before and after weld were conducted and the behaviors of hydrogen concentration were analyzed. On the basis of these analyses, the method of heat treatment to prevent from hydrogen concentration at the weld part was investigated. Results obtained by these analyses showed that pre weld heat treatment is effective in the prevention of hydrogen concentration and combined pre weld heat treatment with post weld heat treatment was found to be the most effective treatment.

scholarly journals Numerical Analysis of the Coupling between Hydrogen Diffusion and Mechanical Behavior near the Crack Tip of Titanium

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Fu-qiang Yang ◽  
Wen-juan Zhan ◽  
Tao Yan ◽  
Hai-bing Zhang ◽  
Xiu-rong Fang
Keyword(s):  
Stress State ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
Coupled Model ◽  
Crack Tip ◽  
The Finite Element Method ◽  
Hydrogen Atoms ◽  
Stress Effects ◽  
Concentration Peak ◽  
Proposed Model

Hydrogen plays a detrimental effect on the degeneration of titanium and its alloys, and it is very important to quantify the hydrogen concentration when estimating the microstructure evaluation of titanium and its alloys in a hydrogen environment. In this paper, the hydrogen atoms are assumed to reside in interstitial sites and in trapping sites such as dislocations, and a mechanic-diffusion coupled model was proposed to describe the stress effects on the diffusion of hydrogen in titanium. A titanium plate with a central crack was modeled to verify the mechanic-diffusion model, and it is solved by the finite element method in commercial software COMSOL. The results indicate that hydrogen diffusion near the crack is determined by the stress state. When the stress state of the crack tip is elastic, the hydrogen will diffuse from both sides of the crack towards the tip and lead to the highest hydrogen concentration in the crack tip. When a plastic zone exists in front of the crack tip, the highest hydrogen concentration at crack surface deviates to the side near the crack tip; a hydrogen concentration peak exists at a characterized distance in front of crack tip initially and then diminishes with the diffusion process. The proposed model is expected to solve the hydrogen concentration under stress in more complex structures.

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