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.

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.

Study on the structural transition of CoNi nanoclusters using molecular dynamics simulations

2018 ◽  
Vol 32 (11) ◽  
pp. 1850133
Author(s):  
J. H. Xia ◽  
Xue-Mei Gao
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Structural Transition ◽  
Correction Function ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Analysis Technique ◽  
Dynamics Simulations ◽  
Embedded Atom Method Potential ◽  
Pair Analysis

In this work, the segregation and structural transitions of CoNi clusters, between 1500 and 300 K, have been investigated using molecular dynamics simulations with the embedded atom method potential. The radial distribution function was used to analyze the segregation during the cooling processes. It is found that Co atoms segregate to the inside and Ni atoms preferably to the surface during the cooling processes, the Co[Formula: see text]Ni[Formula: see text] cluster becomes a core–shell structure. We discuss the structural transition according to the pair-correction function and pair-analysis technique, and finally the liquid Co[Formula: see text]Ni[Formula: see text] crystallizes into the coexistence of hcp and fcc structure at 300 K. At the same time, it is found that the frozen structure of CoNi cluster is strongly related to the Co concentration.

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.

β-Sngrain-boundary structure and self-diffusivity via molecular dynamics simulations

2010 ◽  
Vol 81 (13) ◽  
Author(s):  
Michael S. Sellers ◽  
Andrew J. Schultz ◽  
Cemal Basaran ◽  
David A. Kofke
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Boundary Structure ◽  
Dynamics Simulations

MOLECULAR DYNAMICS SIMULATIONS OF STRUCTURAL PROPERTIES OF CuNi ALLOYS DURING THE COOLING PROCESS AT HIGH PRESSURE

2020 ◽  
Vol 65 (10) ◽  
pp. 10-17
Author(s):  
Thao Nguyen Thi ◽  
Giang Bui Thi Ha ◽  
Linh Tran Phan Thuy ◽  
Hop Nguyen Van ◽  
Chung Pham Do ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
High Pressure ◽  
Molecular Dynamics Simulations ◽  
Sudden Change ◽  
Face Centered Cubic ◽  
Cooling Process ◽  
Embedded Atom ◽  
The Face ◽  
Face Centered ◽  
Dynamics Simulations

Molecular dynamics simulations of Cu80Ni20 (Cu:Ni = 8:2) model with the size of 8788 atoms have been carried out to study the structure and mechanical behavior at high pressure of 45 GPa. The interactions between atoms of the system were calculated by the Quantum Sutton-Chen embedded-atom potentials. The crystallization has occurred during the cooling process with a cooling rate of 0.01 K\ps. The temperature range of the phase transition is determined based on the sudden change of atomic potential during the cooling process. There is also a sudden change in the number of individual atoms in the sample. At a temperature of 300 K, both Ni and Cu atoms are crystallized into the face-centered cubic (FCC) and the hexagonal close-packed (HCP) phases, respectively. The mechanical characteristics of the sample at 300 K were also analyzed in detail through the determination of elastic modulus, number of atoms, and void distribution during the tensile process.

Direct Molecular Dynamics Simulations of Diffusion Mechanisms in NiAl

2000 ◽  
Vol 646 ◽  
Author(s):  
D. Farkas ◽  
B. Soulé de Bas
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Molecular Dynamics Simulations ◽  
Sequential Analysis ◽  
Nearest Neighbor ◽  
Interatomic Potential ◽  
Embedded Atom ◽  
Diffusion Mechanisms ◽  
Dynamics Simulations ◽  
Potential Diffusion

ABSTRACTMolecular dynamics simulations of the diffusion process in ordered B2 NiAl at high temperature were performed using an embedded atom interatomic potential. Diffusion occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated 6-jump cycle is only one of the various cycles observed and some of these are quite complex. A detailed sequential analysis of the observed 6-jump cycles was performed and the results are analyzed in terms of the activation energies for individual jumps calculated using molecular statics simulations.

Cascade Overlap in hcp Zirconium: Defect Accumulation and Microstructure Evolution with Radiation using Molecular Dynamics Simulations

2013 ◽  
Vol 1514 ◽  
pp. 37-42 ◽  
Author(s):  
Prithwish K. Nandi ◽  
Jacob Eapen
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Microstructure Evolution ◽  
Stacking Faults ◽  
Embedded Atom Method ◽  
Shockley Partial Dislocation ◽  
Embedded Atom ◽  
Defect Accumulation ◽  
Dynamics Simulations ◽  
Eam Potential

ABSTRACTMolecular dynamics simulations are performed to investigate the defect accumulation and microstructure evolution in hcp zirconium (Zr) – a material which is widely used as clad for nuclear fuel. Cascades are generated with a 3 keV primary knock-on atom (PKA) using an embedded atom method (EAM) potential with interactions modified for distances shorter than 0.1 Å. With sequential cascade simulations we show the emergence of stacking faults both in the basal and prism planes, and a Shockley partial dislocation on the basal plane.

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