An Atomistic Study of the Equilibrium Segregation of Hydrogen to Tilt Boundaries in Nickel

1991 ◽  
Vol 229 ◽  
Author(s):  
N. R. Moody ◽  
S. M. Foiles
Keyword(s):  
Hydrogen Concentration ◽  
Site Occupancy ◽  
Binding Energies ◽  
Tilt Boundary ◽  
Boundary Structure ◽  
Trap Site ◽  
High Hydrogen ◽  
Embedded Atom ◽  
Concentration Enhancement ◽  
Tilt Boundaries

AbstractIn this study, Monte Carlo simulations have been combined with Embedded Atom Method (EAM) calculations to study hydrogen segregation at the atomic level in an ideal nickel lattice with a Σ9 tilt boundary. The calculations indicate that trap binding energies exceed 0.5 eV on the tilt boundary, but decrease rapidly with distance. Furthermore, the calculations show that trap site occupancy increases with trap site binding energy and hydrogen activity, and reach saturation at high hydrogen concentrations. Most importantly, significant rearrangements in tilt boundary structure are predicted to occur as hydrogen concentration increases. The results are consistent with observations that show significant hydrogen concentration enhancement at grain boundaries in nickel and palladium. They also parallel the effect of hydrogen concentration on crack growth susceptibility in nickel and iron-rich alloys. However, the change in boundary structure as hydrogen concentration increases challenges our understanding of hydrogen-induced fracture.

An Atomistic Study of Hydrogen Effects on the Fracture of Tilt Boundaries in Nickel.

1991 ◽  
Vol 238 ◽  
Author(s):  
N. R. Moody ◽  
S. M. Foiles
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Site Occupancy ◽  
Boundary Structure ◽  
Trap Site ◽  
Embedded Atom ◽  
Defect Sites ◽  
Tilt Boundaries ◽  
Temperature Exposure ◽  
Dynamics Simulations

ABSTRACTIn this study, molecular dynamics simulations were used to fracture Σ9 tilt boundaries in nickel lattices containing a range of trap site hydrogen concentrations. These lattices were created in a previous study using Monte Carlo simulations and the Embedded Atom Method to duplicate room temperature exposure to a hydrogen environment. The molecular dynamics simulations were run at absolute zero to immobilize the hydrogen distributions for determination of trap site occupancy effects on grain boundary fracture. In all lattices, fracture began by the breaking of bonds next to polyhedral defect sites that characterize the boundary structure followed by rapid failure of the remaining bonds. The effect of hydrogen was to lower the stress for fracture from 18 GPa to a lower limiting value of 8 GPa as the trap sites along the boundary plane filled. The simulations showed that the atoms at these sites were the only atoms involved in the fracture process. Within the constraints imposed on these calculations, the results of this study showed that the ‘inherent’ effect of hydrogen in the absence of plastic deformation is to reduce the cohesive force between atoms across the boundary.

On the structure of tilt grain boundaries in cubic metals II. Asymmetrical tilt boundaries

1983 ◽  
Vol 309 (1506) ◽  
pp. 37-54 ◽  
Keyword(s):  
Tilt Boundary ◽  
Boundary Structure ◽  
Reference Structure ◽  
High Angle ◽  
Cubic Metals ◽  
Long Period ◽  
Tilt Boundaries ◽  
Symmetrical Tilt ◽  
Atomistic Study

The results of the study of symmetrical tilt boundaries, reported in the preceding part I, are generalized to asymmetrical tilt boundaries. A classification of tilt boundaries in cubic crystals is developed that reveals which boundaries to choose in order to study equilibrium faceting or intrinsic grain boundary dislocations (g.b.ds) accommodating a misorientation. Two series of atomistic studies of asymmetrical tilt boundary structures are presented based on this classification. The first is a study of long-period (27 ^ 97) [110] asymmetrical tilt boundaries in aluminium. The aims of this study are to investigate whether these boundaries are composed of fundamental structural elements, in the same way as was found in part I for symmetrical tilt boundaries, and to see if localized, distinct stress fields of edge g.b.ds exist throughout the misorientation range. With use of the results of this study, and the principle of continuity of boundary structure enunciated in part I, the boundary unit representation of a 27 — 1193 asymmetrical tilt boundary is derived as an example. It is generally found that the Burgers vectors of intrinsic secondary g.b.ds in tilt boundaries, based on favoured boundary reference structures, are non-primitive d.s.c. vectors. The reason for this is given and a simple formula is presented to derive the Burgers vectors of such dislocations for any favoured tilt boundary reference structure. It is pointed out that, in general, very low angle {0 < 1° say) tilt boundaries cannot be described in terms of units from high angle tilt boundaries, and the transition from the low angle to high angle regimes is discussed. The second atomistic study is an investigation of equilibrium faceting of long-period 27 — 3 [110] tilt boundaries with use of an empirical potential for copper. The limi tations of computer simulation methods using periodic border conditions to study faceting are stated. It is shown, however, that the constraints imposed by the use oi periodic border conditions may be used in a positive sense to carry out the Wultt construction, and thereby deduce equilibrium faceting behaviour.

The dislocation structure of a 10° [110] tilt boundary in silicon

1983 ◽  
Vol 41 ◽  
pp. 114-115
Author(s):  
B. Cunningham ◽  
D.G. Ast
Keyword(s):  
Dislocation Structure ◽  
Tilt Angle ◽  
Imaging Technique ◽  
Diamond Lattice ◽  
Tilt Boundary ◽  
Formation Mechanisms ◽  
Diffraction Contrast ◽  
Lattice Fringe ◽  
Tilt Boundaries ◽  
Chemically Vapor Deposited

There have Been a number of studies of low-angle, θ < 4°, [10] tilt boundaries in the diamond lattice. Dislocations with Burgers vectors a/2<110>, a/2<112>, a<111> and a<001> have been reported in melt-grown bicrystals of germanium, and dislocations with Burgers vectors a<001> and a/2<112> have been reported in hot-pressed bicrystals of silicon. Most of the dislocations were found to be dissociated, the dissociation widths being dependent on the tilt angle. Possible dissociation schemes and formation mechanisms for the a<001> and a<111> dislocations from the interaction of lattice dislocations have recently been given.The present study reports on the dislocation structure of a 10° [10] tilt boundary in chemically vapor deposited silicon. The dislocations in the boundary were spaced about 1-3nm apart, making them difficult to resolve by conventional diffraction contrast techniques. The dislocation structure was therefore studied by the lattice-fringe imaging technique.

Hydrogen permeation through a slab sample in the case of high hydrogen concentration

2006 ◽  
Vol 496 (2) ◽  
pp. 735-739 ◽  
Author(s):  
Maurizio Dapor ◽  
Antonio Miotello ◽  
Arturo Sabbioni
Keyword(s):  
Hydrogen Concentration ◽  
Hydrogen Permeation ◽  
High Hydrogen

Anomalous Positive Bias Stress Instability in MoS2 Transistors With High-Hydrogen-Concentration SiO2 Gate Dielectrics

2019 ◽  
Vol 40 (2) ◽  
pp. 232-235 ◽  
Author(s):  
Guanhua Yang ◽  
Xichen Chuai ◽  
Jiebin Niu ◽  
Jiawei Wang ◽  
Xuewen Shi ◽  
...  
Keyword(s):  
Hydrogen Concentration ◽  
Gate Dielectrics ◽  
Positive Bias ◽  
High Hydrogen ◽  
Bias Stress

Temperature Dependence of Fatigue Crack Growth in Low-Alloy Steel Under Gaseous Hydrogen

2018 ◽  
Author(s):  
Osamu Takakuwa ◽  
Saburo Matsuoka ◽  
Saburo Okazaki ◽  
Michio Yoshikawa ◽  
Junichiro Yamabe ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Binding Energy ◽  
Fatigue Crack Growth ◽  
Temperature Dependence ◽  
Crack Growth ◽  
Site Occupancy ◽  
Hydrogen Gas ◽  
Temperature Elevation ◽  
Trap Site ◽  
Thermal Equilibrium State

In order to elucidate the temperature dependence of hydrogen-enhanced fatigue crack growth (FCG), the FCG test was performed on low-alloy Cr-Mo steel JIS-SCM435 according to ASTM E647 using compact tension (CT) specimen under 0.1–95 MPa hydrogen-gas at temperature ranging from room temperature (298 K) to 423 K. The obtained results were interpreted according to trap site occupancy under thermal equilibrium state. The FCG was significantly accelerated at RT under hydrogen-gas, that its maximum acceleration rate of the FCG was 15 at the pressure of 95 MPa at the temperature of 298 K. The hydrogen-enhanced FCG was mitigated due to temperature elevation for all pressure conditions. The trap site with binding energy of 44 kJ/mol dominated the temperature dependence of hydrogen-enhanced FCG, corresponding approximately to binding energy of dislocation core. The trap site (dislocation) occupancy is decreased with the temperature elevation, resulting in the mitigation of the FCG acceleration. On the basis of the obtained results, when the occupancy becomes higher at lower temperature, e.g. 298 K, hydrogen-enhanced FCG becomes more pronounced. The lower occupancy at higher temperature does the opposite.

Effects of Hydrogen on the Fracture Properties of Σ9 and Σ11 Tilt Boundaries in Nickel

1992 ◽  
Vol 278 ◽  
Author(s):  
J.E. Angelo ◽  
W.W. Gerberich ◽  
N.R. Moody ◽  
S.M. Foiles
Keyword(s):  
Molecular Dynamics ◽  
Monte Carlo ◽  
Fracture Stress ◽  
Equilibrium Distribution ◽  
Embedded Atom Method ◽  
Far Field ◽  
Fracture Properties ◽  
Embedded Atom ◽  
Tilt Boundaries ◽  
Dynamics Simulations

AbstractIn this study, the Embedded Atom Method is combined with Monte Carlo and molecular dynamics simulations to study the fracture properties of Σ9 and Σ11 tilt boundaries in nickel. The Monte Carlo simulations are used to simulate the exposure of the bicrystal to a hydrogen environment at 300° C. These simulations establish the equilibrium distribution of hydrogen at the boundaries as a function of far-field concentration. The effect of the hydrogen on the fracture process is then studied with molecular dynamics. It will be shown that the fracture stress of the Σ9 boundary is affected over a wider range of far-field concentrations than the Σ11 boundary, although the Σ11 boundary shows that catastrophic failure occurs when the sample is charged beyond a certain far-field concentration.

Preparation of a-axis YBa2Cu3Ox epitaxial films using direct current-95 MHz hybrid plasma sputtering

1995 ◽  
Vol 10 (9) ◽  
pp. 2216-2234 ◽  
Author(s):  
Wataru Ito
Keyword(s):  
Substrate Surface ◽  
Tilt Boundary ◽  
Boundary Structure ◽  
Ion Density ◽  
Ybco Films ◽  
Plasma Sputtering ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Hybrid Plasma ◽  
Symmetrical Tilt

The dc-95 MHz hybrid plasma magnetron sputtering has been newly developed for obtaining a-axis oriented YBa2Cu3Ox (YBCO) films with an excellent crystallinity. The crystallinity was found to be the best among the films reported so far: the full width at half maximum value of 0.027°in the rocking curve measurement through the film (200) diffraction peak and Xmin of 2% estimated from the barium signal behind the surface peak in Rutherford backscattering (RBS) measurement using a 1 MeV He+ ion. The success in the excellent crystallinity was explained from the ion acceleration model at the ion sheath formed near the substrate surface considering the high ion density, which was revealed to be a characteristic of hybrid plasma. Almost perfect epitaxial growth was also confirmed by transmission electron microscopy. A characteristic grain boundary structure depending on the substrate was observed for the films on NdGaO3 and SrTiO3 substrates. Twist boundary is dominant for the film on NdGaO3, while symmetrical tilt boundary and basal-plane-faced tilt boundary exclusively exist for the film on SrTiO3. The microstructure of the film on SrTiO3 is very resistive against film relaxation. Strain relief was observed by RBS channeling spectra for the relatively high superconducting films. The results of Raman spectroscopy and RBS oxygen resonant measurements indicated that the oxygen content is not a critical parameter for determining the superconductivity of the a-axis oriented YBCO films, but oxygen ordering in the plane of the Cu-O chain and relief of the film strain are important for the improvement of Tc.

Prediction of Energies of Tilt Boundaries in Al-Pb Alloy

2007 ◽  
Vol 1056 ◽  
Author(s):  
Y. Purohit ◽  
D. L. Irving ◽  
R. O. Scattergood ◽  
D. W. Brenner
Keyword(s):  
Grain Boundaries ◽  
First Principles ◽  
Density Functional ◽  
First Principles Calculations ◽  
Pure System ◽  
Embedded Atom ◽  
Unit Model ◽  
Tilt Boundaries ◽  
Embedded Atom Method Potential ◽  
Analytic Potential

ABSTRACTEnergies for symmetric tilt grain boundaries in pure Al and in Al with substitutional Pb defects at coincident sites along the grain boundaries were calculated using a modified embedded atom method potential and density functional theory. The agreement between the analytic potential, the first principles calculations and experiment is reasonably good for the pure system. For the Al-Pb system both the analytic potential and first principles calculations predict that Pb segregation to the interface is energetically preferred compared to the dilute solution. The application of a disclination structural unit model to calculating grain boundary energies over the entire range of tilt angles is also explained.

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