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Clarifying the deformation behaviors of microstructures could greatly help us understand the precipitation-strengthening mechanism in alloys. However, it is still a formidable challenge to study the slow plastic deformation of alloys at the atomic scale. In this work, the phase-field crystal method was used to investigate the interactions between precipitates, grain boundary, and dislocation during the deformation processes at different degrees of lattice misfits and strain rates. The results demonstrate that the pinning effect of precipitates becomes increasingly strong with the increase of lattice misfit at relatively slow deformation with a strain rate of 10−4. The cut regimen prevails under the interaction between coherent precipitates and dislocations. In the case of a large lattice misfit of 19.3%, the dislocations tend to move toward the incoherent phase interface and are absorbed. The deformation behavior of the precipitate-matrix phase interface was also investigated. Collaborative deformation is observed in coherent and semi-coherent interfaces, while incoherent precipitate deforms independently of the matrix grains. The faster deformations (strain rate is 10−2) with different lattice misfits all are characterized by the generation of a large number of dislocations and vacancies. The results contribute to important insights into the fundamental issue about how the microstructures of precipitation-strengthening alloys deform collaboratively or independently under different lattice misfits and deformation rates. [ABSTRACT FROM AUTHOR]

Clarifying the deformation behaviors of microstructures could greatly help us understand the precipitation-strengthening mechanism in alloys. However, it is still a formidable challenge to study the slow plastic deformation of alloys at the atomic scale. In this work, the phase-field crystal method was used to investigate the interactions between precipitates, grain boundary, and dislocation during the deformation processes at different degrees of lattice misfits and strain rates. The results demonstrate that the pinning effect of precipitates becomes increasingly strong with the increase of lattice misfit at relatively slow deformation with a strain rate of 10−4. The cut regimen prevails under the interaction between coherent precipitates and dislocations. In the case of a large lattice misfit of 19.3%, the dislocations tend to move toward the incoherent phase interface and are absorbed. The deformation behavior of the precipitate-matrix phase interface was also investigated. Collaborative deformation is observed in coherent and semi-coherent interfaces, while incoherent precipitate deforms independently of the matrix grains. The faster deformations (strain rate is 10−2) with different lattice misfits all are characterized by the generation of a large number of dislocations and vacancies. The results contribute to important insights into the fundamental issue about how the microstructures of precipitation-strengthening alloys deform collaboratively or independently under different lattice misfits and deformation rates.

Amorphous uranium dioxide (UO 2) has been modelled on the atomic scale using a combination of quantum mechanical (density functional theory) and classical forcefield methods (molecular dynamics and reverse Monte-Carlo). The atomic scale structure of the amorphous state has been predicted and is presented in the form of simulated X-ray diffraction patterns, pair correlation functions and bond angle distributions. These are shown to be consistent with the experimental patterns previously reported. To enable accurate calculation of the energies and magnetic properties, using quantum mechanics, reverse Monte-Carlo was used to generate reduced cells from larger molecular dynamic melt-quenches. This allowed density functional theory energy minimisation for structures consistent with the amorphous state. Building on this, the material's propensity to deviate from stoichiometry, the magnetic structure and amorphous UO 2 surface energy were computed. Non-stoichiometry is accommodated more readily in the amorphous system than in crystalline UO 2. This indicates that deviations from stoichiometry in fuel (for example as a result of operation) will be accommodated at amorphous phases, if present, leaving a more stoichiometric crystalline phase – impacting processes including fission gas mobility, melting points and a number of other safety relevant properties. The magnetic structure of bulk amorphous UO 2 is predicted to be a spin-glass, unlike crystalline UO 2 which has anti-ferromagnetic ordering at 0 K. The surface energy of amorphous UO 2 is computed to be 0.79 Jm−2, which is similar to the experimentally observed surface energy of grain boundary bubbles in UO 2 and comparable to the surface energies reported for crystalline UO 2. Results are pertinent to ongoing efforts to understand the nature of grain boundaries in nuclear fuels, to model fission gas release from them, radiation induced amorphization and the impact of dopants and impurities on nuclear fuel's manufacture and in-reactor behaviour. Image, graphical abstract [ABSTRACT FROM AUTHOR]

There is currently a growing interest in the realisation and optimization of hybrid plasma/catalyst systems for a multitude of applications, ranging from nanotechnology to environmental chemistry. In spite of this interest, there is, however, a lack in fundamental understanding of the underlying processes in such systems. While a lot of experimental research is already being carried out to gain this understanding, only recently the first simulations have appeared in the literature. In this contribution, an overview is presented on atomic scale simulations of plasma catalytic processes as carried out in our group. In particular, this contribution focusses on plasma-assisted catalyzed carbon nanostructure growth, and plasma catalysis for greenhouse gas conversion. Attention is paid to what can routinely be done, and where challenges persist. [ABSTRACT FROM AUTHOR]

The effect of cluster configuration on vacancy mediated uranium migration is investigated for stoichiometric UO 2 and hyper-stoichiometric UO 2+ x . The minimum enthalpy pathway involves reconfiguration of the most stable cluster to a metastable configuration, in stoichiometric and hyper-stoichiometric systems. Additionally, a much larger number of alternative metastable configurations were identified for UO 2+ x compared to UO 2 . This would lead to a larger contribution to the Arrhenius pre-exponential term with hyper-stoichiometry. Consequently, the often made assumption that re-orientation of the ground state cluster offers access to the migration activation energy cannot be assumed to be valid. [ABSTRACT FROM AUTHOR]

Abstract: A new kinetic Monte Carlo (KMC) method is presented to investigate the atomic layer deposition (ALD) of alumina onto silicon. Atoms are located on predefined sites and thus do not move continuously. This lattice-based KMC approach requires preliminary physical considerations on the crystal structures that we aim to reproduce, especially in the case of heterogeneous systems like high-κ oxides deposition on silicon. Atomistic configuration changes are performed by local events: these are elementary reactional mechanisms occurring on specific sites. The temporal dynamics is governed by transition probabilities, calculated for every event from activation barriers, ALD process parameters and random numbers. Mechanism activation energies may come from ab initio calculations, literature or experiments. We show that this kind of algorithm is computation-time-cheap enough to allow huge systems simulations: up to millions of atoms and events during a few hours on an ordinary computer. [Copyright &y& Elsevier]

We present the results of large scale non equilibrium molecular dynamics simulations of plasticity induced by a shock wave in a perfect fcc single crystal in the orientation [1 0 0]. Shockley loops are thermally nucleated behind the shock front. The algorithm used to identify and follow the time evolution of the dislocation loops is detailed. It enables the measure of the critical size that a slip fluctuation can reach before it shrinks back to a perfect configuration. [Copyright &y& Elsevier]