Hydrogen Trapping Effect Research Articles

Hydrogen behaviour in aged low activation martensitic steel F82H for fusion reactor applications

A time dependent permeation method is used to measure the permeability, diffusivity, and solubility of hydrogen in the low activation martensitic steel F82H, based on 7–10%Cr steel agedfor 2000 h under vacuum at 773 K. The measurements cover the temperature range 373–723 K which includes the onset of hydrogen trapping effects on diffusivity and solubility. The results are interpreted using a trapping model. The number of trap sites and their average energies for hydrogen in the aged F82H steel are determined. These data are compared with those obtainedfor deuterium in F82H steel.

Hydrogen Trapping in Fe–Ti Alloys

The hydrogen trapping effects in Fe-Ti alloys were studied by repetitive electrochemical permeation measurements and gas pressure oscillating permeation measurements. A theoretical analysis has been made of the effects of both reversible and irreversible trapping sites on hydrogen diffusion using the Crank-Nicolson finite difference method. The break-through times are different for the first and second electrochemical polarizations in Fe-Ti alloys. The difference of the break-through times for the first and second polarizations is due to the irreversible trapping sites in the alloys, and the difference of break-through times in the second polarization for the alloys and pure iron is due to the reversible trapping sites

A Reexamination of the Trapping of Hydrogen in Iron and Steel

The apparent hydrogen diffusivity data for pretreated pure iron and steel membranes have been analysed for hydrogen-trapping effects. Modified equations, valid for the appropriate boundary conditions of charging, have been derived to compute the trap density from the apparent diffusivity. In general, the traps are saturable in nature. The dependence of diffusivity of hydrogen in iron and steel on the charging current density or overvoltage indicates trapping of hydrogen at dislocations and grain/interfacial boundaries

Effects of prior hydrogen dissolution and hydridingon hydrogen solubility in LaNi 5

Pressure-composition-temperature ( P-C-T) relations for the LaNi 5−H system weremeasured using well annealed LaNi 5 block and powder samples with a stoichiometry of x=5.0 in LaNi x . The block sample exhibited lower hydrogen solubility than the powder sample for hydrogen concentrations [H]/[LaNi 5]<1×10 −1, which may be ascribed to higher internal stresses accumulated in the block sample by H 2 dissolution. Marked hydrogen trapping and hydrogen solubility enhancement in LaNi 5 took place not only in the samples activated by hydriding-dehydriding cycling, but also in the samples cycled in advance in a solid solution. The mean value of the relative partial molar enthalpy for H 2 dissolution at infinite dilution is −20.2 kJ(mol H) −1, constant up to hydrogen concentrations of [H]/[LaNi 5]=1.5×10 −2. However, the negativity of the enthalpy value becomes markedly increased by the hydrogen trapping effect induced in LaNi 5 even by cyclic H 2 dissolution in a hydrogen solid solution region.

Investigation of structure dependence of diffusivity, solubility, and permeability of hydrogen in hot rolled low carbon steels

A time dependent permeation method has been used to measure the diffusivity, permeability, and solubility of hydrogen in hot rolled low carbon steels. The measurements cover the temperature range 200–600°C which includes the onset of hydrogen trapping effects. The results have been interpreted using Oriani's model to explain the effects of microstructure on the trapping. The results show that the initial microstructure of the steel affects significantly the behaviour of the hydrogen atoms. Of the three possible trapping sites, namely, dislocations, interstitial atoms, and precipitated particles, it seems that the most effective traps are the interfaces between coarse particles and the matrix.MST/973

Phase equilibria in the niobium-vanadium-hydrogen system

The effect of vanadium additions to niobium on the metal-hydrogen phase equilibria has been studied. Measurements of the equilibrium H 2(D 2) pressure-composition-temperature isotherms for Nb 1 − x V x alloys with 0 ⩽ x < 0.2 were used to determine the depression of the α — α' critical temperature with increasing vanadium concentration. A simple lattice-fluid model guided reduction of the data. Changes in the triple point temperature as well as the shift of the ζ → ϵ phase transition were determined by differential scanning calorimetry measurements. A rapid overall depression was found, of the order of 7 K (at.% substituted V) −1, for the metal-hydrogen (deuterium) phase boundary structure when compared with the Nb-H system in the hydrogen concentration range of interest. The results explain the enhanced terminal solubility of hydrogen in this system found by Miller and Westlake. The changes in the phase equilibria are discussed in terms of the effect of hydrogen trapping and compared with the results of a cluster-variation calculation for random-field systems of MacGillivray et al., taking into account a distribution of H-site energies due to alloying.

Modeling of hydrogen diffusion in metals

The study of the diffusion of hydrogen in metals is very important to further understand the hydrogen embrittlement of metals. To describe the diffusion of hydrogen in metals the diffusion equation deduced from Fick's law under an ideal condition has been generally used and the effect of hydrogen trapping in metals has been neglected. In the process of hydrogen diffusion through a metal, hydrogen fills the traps continuously and the fraction of the traps filled by hydrogen, which have only little effect on the diffusion of hydrogen, may be different at different places because the distribution of hydrogen concentration may be different at different places. Thus the hydrogen diffusion coefficient in the metal may also be different at different positions, i.e., the diffusion coefficient should be affected by time in a dynamic process of hydrogen diffusion through a metal. But in the previous analyses, the above fact is not considered and the hydrogen diffusion coefficient is generally taken as a constant. In the present paper a new model of hydrogen diffusion in metals in which the effect of time is taken into account is developed.

The effect of palladium on hydrogen absorption and mobility in AISI 4130 steels

The effect of palladium in solid solution on the hydrogen absorption and mobility were investigated by cathodic polarization and hydrogen permeation techniques in 1 N NaOH. Palladium additions led to a higher hydrogen permeation rate due to an increased diffusivity and a decreased hydrogen trapping effect. No significant differences were seen in the cathodic polarization parameters as a result of palladium additions. Results of this investigation in conjunction with previous field ion microscopy and autoradiography investigations show that palladium segregates to potential hydrogen traps like MnS inclusions and subsequently repels hydrogen, thereby rendering potential traps innocuous. Results of a palladium ion beam implanted steel are also presented to compare the behavior of palladium surface enriched steels with the steels which have palladium in solid solution.

A molecular effect of hydrogen trapping in the implantation of molecular hydrogen ions into aluminum and aluminum oxide

Molecular effects of hydrogen trapping are examined for the implantation of H+2 and H+3 molecular ions into aluminum and aluminum oxide. It was found that the H+3 bombardment enhances trapping efficiencies more than H+2 by a factor of 2.7 for Al and 4.3 for Al2O3. These results indicate the importance of the interaction between hydrogen and vacancy clusters.

Hydrogen permeation through type 316 stainless steels and ferritic steel for a fusion reactor

The hydrogen permeabilities, P, and diffusivities, D, in SUS316-ST1, JPCA-2 and ferritic steel JFMS have been measured by a permeation technique during stepwise heating from 150 to 450°C. In the temperature range above 300°C, the results are expressed as P = 3.4 × 10 −5 exp( −0.63 eV kT ) cm 3 H 2(STP)/cm s Pa 1 2 and D = 4.7 × 10 −3 exp( −0.48 eV kT ) cm 2/s for type 316 stainless steels, and P = 1.9× 10 −6 exp( −0.36 eV kT ) cm 3 H 2(STP)/cm s Pa 1 2 and D = 4.2× 10 −4 exp(−0.091 eV/ kT cm 2/ s for ferritic steel. The hydrogen trapping effect was pronounced below 300°C. and the trap binding energy was 0.3–0.4 eV for all materials.

Nb films sputtered with a (Ar, H2) mixture and application to superconductor-insulator-superconductor junctions

Effects of hydrogen trapping in Nb base electrodes on the superconductivity of Nb itself and superconductor-insulator-superconductor (SIS) junction characteristics have been investigated. The Nb films were prepared by sputter deposition in an atmosphere of (Ar, H2) mixture. The gap parameter ΔNb and the critical temperature Tc gradually decreased with increasing H2 partial pressure. The SIS junctions exhibited a sudden extinction of the Josephson current Ic when ΔNb was lowered to or less than 1.1 meV by H2 trapping. Such a junction could be used as a quasiparticle tunneling junction for microwave detection with no requirement for an external magnetic field.

溶接低温割れに及ぼす非金属介在物の影響 ＩＩ 水素割れ発生，伝搬に対する検討

In the previous work, it was obtained that reducing inclusion contents increased the risk of weld cold cracking.In this work, further examination of the effect of nonmetallic inclusions on HAZ hydrogen induced cracking was carried out. The sensitivity of hydrogen induced cracking was evaluated by hydrogen charged three point bending test for synthetic HAZ.The results in this work were as follows:(1) At room temperature, inclusions acted as crack initiation site, so KIC of hydrogen-free synthetic HAZ specimens decreased with increasing inclusion contents.(2) In hydrogen-charged specimens, increasing inclusions result in the elevation of KTH and decrease of crack growth rate. It was aquired that inclusions reduced the sensitivity of HAZ hydrogen embrittlement.(3) It was considered that this effect of inclusions on reducing sensitivity of hydrogen embrittlement was mainly caused by the hydrogen trapping effect of inclusions.(4) Ce treatment had no significant effect on crack initiation and propagation of hydrogen induced cracking.

An example of the effect of hydrogen trapping on hydrogen embrittlement

The role of internal hydrogen in reducing the tensile reduction of area of iron-titanium alloys is examined. The population of hydrogen at potential crack nucleii is shown to be controlled by its dynamic interaction with mobile dislocations and its subsequent transport to fixed traps. Expressions are developed for both the number of hydrogen atoms at a given irreversible trap, as well as the time necessary to reach such a number. Reducing the number below the critical value to nucleate a crack, or increasing the time to reach this value will improve an alloy’s performance, and this improvement is related to controllable external and metallurgical variables. These predictions of the model are shown to be consistent with companion experimental data, and with the trap theory of hydrogen embrittlement.

Hydrogen Absorption in the Niobium-Vanadium System *

The effect of dilute vanadium additions to niobium on hydrogen absorption has been studied by measuring equilibrium pressure--composition--temperature data for a Nb + 6 at.% V alloy and by constructing a theoretical model of the effect of hydrogen trapping on phase equilibria in such systems. The results indicate the H--V binding energy is substantially smaller than thought previously. A depression of the ..cap alpha..--..cap alpha..' critical temperature is observed which, if interpreted in terms of trapping, leads to a H--V binding energy of approx. 0.04 eV.

18Niマルエージ鋼中の水素拡散

An investigation of the effect of aged structures on diffusivity and solubility of hydrogen in a commercial 18Ni maraging steel has been carried out at room temperature by the electrochemical permeation technique.The diffusion coefficient and solubility of hydrogen vary with the aged structures of the steel. When the steel is aged at 400 to 450°C for 1 to 3 h, the former shows a minimum, while the latter exhibits a maximum. These variations in diffusivity and solubility of hydrogen can be interpreted in terms of the difference between hydrogen trapping effects of various lattice imperfections, such as dislocations and their stress fields, together with the interfaces between the precipitates and the matrix of martensites introduced by the formation of zones and/or by the precipitation of metastable phases during aging. The solubility of hydrogen is high and the diffusion coefficient is low in the structures aged at higher temperatures for long times. This corresponds to the overaging structure caused by the combination of usual overaging and the formation of nickel rich-austenites in the structure. Thus, the diffusion coefficient in the austenitic structure formed by the reversion of martensites during aging seems to be lower than that in the martensitic structure caused by solution treatment.