MEAM interatomic potentials of Ni, Re, and Ni-Re alloys for atomistic fracture simulations

Second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potentials are developed for the Ni, Re, and Ni-Re binaries. To construct the potentials, density functional theory (DFT) calculations have been employed to calculate fundamental physical properties that play a dominant role in fracture. The potentials are validated to accurately reproduce material properties that correlate with material’s fracture behavior. The thus constructed potentials were applied to perform large scale simulations of mode I fracture in Ni and Ni-Re binaries with low Re content. Substitutional Re did not alter the ductile nature of crack propagation, though it resulted in a monotonous increase of the critical stress intensity factor with Re content.

A Hybrid Molecular Dynamics Kinetic Monte Carlo Simulation Methodology

<p>This thesis describes a novel hybrid computational methodology in which the Molecular Dynamics and Kinetic Monte Carlo methods are concurrently combined. This hybrid methodology has been developed to simulate phenomena which are unfeasible to treat with either Molecular Dynamics or Kinetic Monte Carlo alone, due to the wide range of time scales involved and the need for highly detailed atom dynamics. Is is shown that the hybrid methodology can reproduce the results of a larger (more atoms) all Molecular Dynamics simulation at a significant reduction in computational cost (run time) - due to the replacement of Molecular Dynamics atoms with Kinetic Monte Carlo atoms. The hybrid methodology has been successfully used to study the dynamics of epitaxial stacking fault grain boundaries. This work identified that grain boundary motion was hindered by atoms lodging in off-lattice sites, and also by overlayer islands built up by adatom deposition. It was verified that the ‘kink flip” move is a key element in the motion of grain boundaries. Methods for enhancing the hybrid methodology were researched. It was shown that by an optimal choice of damping parameter γ, wave reflections back into the Molecular Dynamics domain could be minimised. This is expected to enable the hybrid methodology to operate successfully with smaller Molecular Dynamics domains, making larger and/or longer simulation runs feasible. This research included the derivation of the dispersion relation for the discrete case with damping and net reflectivity formulas. These are believed to be new results. The hybrid model can be applied to a wide variety of MD and KMC methods. Other MD potentials such as Embedded Atom or Modified Embedded Atom could be employed. The KMC component can be developed to use a more refined lattice or an ”on the fly” KMC method could be employed. Both the MD and KMC components can be extended to handle more than one species of atom. Parallelised versions of the MD and KMC components could also be developed. Any situation where the problem can be decomposed into distinct domains of fine scale and coarse scale modelling respectively, is potentially suitable for treatment with a hybrid model of this design.</p>

A Hybrid Molecular Dynamics Kinetic Monte Carlo Simulation Methodology

<p>This thesis describes a novel hybrid computational methodology in which the Molecular Dynamics and Kinetic Monte Carlo methods are concurrently combined. This hybrid methodology has been developed to simulate phenomena which are unfeasible to treat with either Molecular Dynamics or Kinetic Monte Carlo alone, due to the wide range of time scales involved and the need for highly detailed atom dynamics. Is is shown that the hybrid methodology can reproduce the results of a larger (more atoms) all Molecular Dynamics simulation at a significant reduction in computational cost (run time) - due to the replacement of Molecular Dynamics atoms with Kinetic Monte Carlo atoms. The hybrid methodology has been successfully used to study the dynamics of epitaxial stacking fault grain boundaries. This work identified that grain boundary motion was hindered by atoms lodging in off-lattice sites, and also by overlayer islands built up by adatom deposition. It was verified that the ‘kink flip” move is a key element in the motion of grain boundaries. Methods for enhancing the hybrid methodology were researched. It was shown that by an optimal choice of damping parameter γ, wave reflections back into the Molecular Dynamics domain could be minimised. This is expected to enable the hybrid methodology to operate successfully with smaller Molecular Dynamics domains, making larger and/or longer simulation runs feasible. This research included the derivation of the dispersion relation for the discrete case with damping and net reflectivity formulas. These are believed to be new results. The hybrid model can be applied to a wide variety of MD and KMC methods. Other MD potentials such as Embedded Atom or Modified Embedded Atom could be employed. The KMC component can be developed to use a more refined lattice or an ”on the fly” KMC method could be employed. Both the MD and KMC components can be extended to handle more than one species of atom. Parallelised versions of the MD and KMC components could also be developed. Any situation where the problem can be decomposed into distinct domains of fine scale and coarse scale modelling respectively, is potentially suitable for treatment with a hybrid model of this design.</p>

Stability of supratransmission waves in a crystal of A3B stoichiometry upon interaction with single dislocations

Supratransmission waves are stable objects that can exist in different discrete environments. In this paper, we consider the interaction of such waves with single edge dislocations of various configurations in a crystal with A3B stoichiometry. The model was a Pt3Al crystal, the potential obtained by the embedded atom method was used to describe the interaction of its atoms. Quantitative characteristics of the wave were obtained before and after the interaction. It is found that the degree of energy dissipation by dislocations depends on the mutual orientation of the wave front and the extra plane of the dislocation. Numerical estimates are made for four different configurations. The results obtained can be useful in studying the propagation of soliton-type waves in defect crystals of various compositions.

Modified Embedded-Atom Interatomic Potential Parameters of the Ti–Cr Binary and Ti–Cr–N Ternary Systems

The second nearest-neighbor modified embedded-atom method (2NN MEAM) potential parameters of the Ti–Cr binary and Ti–Cr–N ternary systems are optimized in accordance with the 2NN MEAM method. The novel constructed potential parameters can well reproduce the multiple fundamental physical characteristics of binary and ternary systems and reasonably agree with the first-principles calculation or experimental data. Thus, the newly constructed 2NN MEAM potential parameters can be used for atomic simulations to determine the underlying principle of the hardness enhancement of TiN/CrN multilayered coatings.

Atomistic simulations of Ag–Cu–Sn alloys based on a new modified embedded-atom method interatomic potential

An interatomic potential for the ternary Ag–Cu–Sn system, an important material system related to the applications of lead-free solders, is developed on the basis of the second nearest-neighbor modified embedded-atom-method formalism. Potential parameters for the ternary and related binary systems are determined based on the recently improved unary description of pure Sn and the present improvements to the unary descriptions of pure Ag and Cu. To ensure the sufficient performance of atomistic simulations in various applications, the optimization of potential parameters is conducted based on the force-matching method that utilizes density functional theory predictions of energies and forces on various atomic configurations. We validate that the developed interatomic potential exhibits sufficient accuracy and transferability to various physical properties of pure metals, intermetallic compounds, solid solutions, and liquid solutions. The proposed interatomic potential can be straightforwardly used in future studies to investigate atomic-scale phenomena in soldering applications. Graphical abstract

Effects of Re on Vacancy Mobility in a Ni-Re System: An Atomistic Study

The performance of modern Ni-based superalloys depends critically on the kinetic transport of point defects around solutes such as rhenium. Here, we use atomistic calculations to study the diffusion of vacancy in the low-concentration limit, using the crystalline fcc-framework nickel as a model. On-the-fly kinetic Monte Carlo is combined with an efficient energy-valley search to find energies of saddle points, based on energetics from the embedded atom method. With this technique, we compute the local energy barriers to vacancy hopping, tracer diffusivities, and migration energies of the low-concentration limit of Ni-Re alloys. It was estimated that the computed diffusion rates are comparable to the reported rates. The presence of Re atoms affects the difference between the energy of the saddle point and the initial energy of point defect hopping. In pure Ni, this difference is about 1 eV, while at 9.66 mol% Re, the value is raised to about 1.5 eV. The vacancy migration energy of vacancy in the 9.66 mol % Re sample is raised above that of pure Ni. Our findings demonstrate that even in the low-concentration limit, Re solute atoms continue to play a crucial role in the mobility of the vacancies.