Density functional theory calculations and molecular dynamics with a recently developed potential for W–He were used to evaluate the thermal stability of helium-vacancy clusters (nHe.mv) as well as pure interstitial helium clusters in tungsten. The stability of such objects results from a competitive process between thermal emission of vacancies, self interstitial atoms (SIAs), and helium, depending on the helium-to-vacancy ratio in mixed clusters or helium number in pure interstitial helium clusters. We investigated in particular the ground state configurations as well as the activation barriers of self trapping and trap mutation, i.e., the emission of one SIA along with the creation of one vacancy from a vacancy-helium or pure helium object.

This study aims at presenting a way to obtain nanostructured materials. Austenitic stainless steel (316L) nanopowders and ferritic/martensitic alloy steels (Fe14Cr) are sintered with the Spark Plasma Sintering (SPS) technique. This technique leads to a fully dense/nano-sized microstructure material after a short treatment. The optimal sintering temperature was found to be 850°C for both materials. The relationship between the Vickers Hardness and scale of the microstructure is in good agreement with the Hall-Petch Law.

The opto-electronic properties of CuInSe2 and related compounds depend on their defect chemistry in a way that is far from being understood and in which ab initio calculations could help by providing new insights as shown previously. Ab initio calculations of energy and electronic structure of various intrinsic (including defect pairs) and extrinsic (including potential dopants such as Zn) point defects have been performed in the chalcopyrite semiconductors CuInSe2, some of them being computed for the first time by advanced ab initio techniques. The method used is based on the density functional theory within the framework of pseudo-potentials and plane waves basis set. The results are discussed in view of the existing data, models and calculations.

The Pressurized Water Reactor vessel steels are embrittled by neutron irradiation. Among the solute atoms, copper play an important role in the embrittlement and different Cu-rich defects have been experimentally observed to form. We have investigated by Kinetic Monte Carlo (KMC) on rigid lattices the evolution of the primary damage. Since the point defects created by the displacement cascades have very different kinetics, their evolution is tracked in two steps. In a first step, we have studied their recombination in the cascade region and the formation of interstitial clusters using “object diffusion”. The parameters of this model are based on MD simulations, or on first principles calculations. In a second part, we have investigated the subsequent evolution of the primary damage with a model based on a vacancy jump mechanism. These simulations which rely on an adapted EAM potential show the formation of copper rich defects. Some of the potential's predictions that played a key role in the model were checked by ab initio calculations. The defects obtained from these simulations, subsequent to the primary damage created by displacement cascades, exhibit similarities with the ones observed by atom probe. The influence of temperature and Cu content on the final damage was investigated.

The role of the interatomic potentials on the primary damage has been investigated by Molecular Dynamics (MD) simulations of displacement cascades with three different interatomic potentials dedicated to α-Fe. The primary damage, caused by the neutron interaction with the matter, has been found to be potential sensitive. We have investigated the equilibrium parts of the potential as well as the “short distance interactions” which appear to have a strong influence on the cascade morphology and defects distribution at the end of the cascade. The static properties as well as dynamical (thermal) characteristics of the potentials have been considered; the kinetic and potential energy transfers during the collisions have also been studied.

In nuclear power plants, Zr–based cladding is corroded by the primary coolant. Concomitantly, it undergoes hydrogen pick–up which induces modifications of its mechanical properties, especially creep and recrystallization rates. Below 600K, the deformation in hcp Zr is partially controlled by screw dislocations, which due to their intricate core structure have reduced intrinsic mobility. Here, we address the possible hydrogen induced modifications of the core structure of screw dislocations. We used first–principle calculations based on the density functional theory to evaluate the interaction between hydrogen and screw dislocation cores and also to evaluate the hydrogen induced modifications of the prismatic and basal gamma surfaces. We show that the presence of hydrogen results in significant reductions of the stacking fault energies.

The steel vessels of pressurized water reactors are embrittled by neutron irradiation. It is well known that copper atoms play an important role in the embrittlement and that different Cu- containing defects such as Cu-rich clusters (sometimes called atmospheres), Cu precipitates and Cu-vacancy complexes have been identified experimentally. It is still difficult to link the formation of these defects to the primary damage resulting from the neutron inducing displacement cascades. Therefore, we investigate the evolution of the primary damage in FeCu alloys using kinetic Monte Carlo simulations based on a vacancy diffusion mechanism. The calculations rely on adapted, phenomenological, n-body potentials that satisfactorily reproduce properties of FeCu. At room temperature, experimentally identified defects such as Cu-vacancy complexes (one Cu atom bound to three or four vacancies) form in the course of our simulations. Furthermore, it appears that complex defects such as a Cu atom linked to two vacancies are very mobile and are responsible for the formation of small Cu clusters.

The steel vessels of pressurized water reactors are embrittled by neutron irradiation. It is well known that copper atoms play an important role in the embrittlement and that different Cu-containing defects such as Cu-rich clusters (sometimes called atmospheres), Cu precipitates and Cu-vacancy complexes have been identified experimentally. It is still difficult to link the formation of these defects to the primary damage resulting from the neutron inducing displacement cascades. Therefore, we investigate the evolution of the primary damage in FeCu alloys using kinetic Monte Carlo simulations based on a vacancy diffusion mechanism. The calculations rely on adapted, phenomenological, n-body potentials that satisfactorily reproduce properties of FeCu. At room temperature, experimentally identified defects such as Cu-vacancy complexes (one Cu atom bound to three or four vacancies) form in the course of our simulations. Furthermore, it appears that complex defects such as a Cu atom linked to two vacancies are very mobile and are responsible for the formation of small Cu clusters.