Classical molecular dynamic simulation of (111) Si and Al surface sputtering under bombardment by polyatomic clusters

The self-sputtering processes of (111) Si and Al surfaces under bombardment by Si (N) and Al (N) ions and clusters (N = 1-60) with the same energy per particle-projectile atom (1 keV/atom) are studied in this paper. The nonlinear effects produced in the target during the development stage of an atomic-collision cascade and during the postcascade stage are analyzed, and a correlation between these effects and secondary emission characteristics is found. The study has been carried out in the framework of classical molecular dynamics. As a result, a number of features of (111) Si and Al surface sputtering and erosion have been revealed. Thus, it has been established that the sputtering yield increases nonadditively as the size N of the implanted cluster increases at N > 10, which is related to the appearance of nonlinear cascades and the postcascade heat spike, and is accompanied by microcrater formation. It is shown that the implantation of clusters into the Si target leads to the formation of amorphous regions

Effect of carbon decoration on the absorption of < 100 > dislocation loops by dislocations in iron

This work closes a series of molecular dynamics studies addressing how solute/interstitial segregation at dislocation loops affects their interaction with moving dislocations in body-centred cubic Fe-based alloys. We consider the interaction of interstitial dislocation loops decorated by different numbers of carbon atoms in a wide temperature range. The results reveal clearly that the decoration affects the reaction mechanism and increases the unpinning stress, in general. The most pronounced and reproducible increase of the unpinning stress is found in the intermediate temperature range from 300 up to 600 K. The carbon-decoration effect is related to the modification of the loop-dislocation reaction and its importance at the technologically relevant neutron irradiation conditions is discussed

Glide of dislocations in < 1 1 1 >{321} slip system: an atomistic study

Atomistic calculations are performed to investigate plastic slip in the {321} system in body-centred cubic iron. Several modern interatomic potentials, developed over the last decade, are applied to compute the stacking fault -line energy in the {321} plane and the results are compared with the ab initio prediction. The applied potentials have shown strong deviations, but several potentials acquired good qualitative agreement with the ab initio data. Depending on the applied potential, the lowest value of the Peierls stress for the edge dislocation (ED) is 50MPa (Ackland and Bacon from 1997) and the highest is 550MPa (Dudarev and Derlet from 2005), while for the screw dislocation it is much higher, in the range 1-2GPa. At finite temperature, however, the flow stress of the ED is found to decrease exponentially reaching a negligible value at about 200K, irrespective of the applied potential. On the basis of the data obtained using Ackland-Mendelev potential from 2004, we conclude that the slip resistance of the {321} system is in between the resistance of the {110} and {112} slip systems

Deuterium accumulation in tungsten under low-energy high-flux plasma exposure

The accumulation of deuterium implanted in tungsten is simulated within the framework of kinetic diffusion theory. The influence of the tungsten microstructure (dislocation density and impurity concentration) on the process of deuterium capture and accumulation is considered. It is established that, under the chosen irradiation conditions, deuterium accumulation in the near-surface region is determined by capture at defects formed during implantation. The deuterium concentration gradient, together with the material microstructure, determines its accumulation in tungsten. Variation in the dislocation density and impurity concentration does not affect the simulation results, which is, first, related to the fact that the model used does not contain alternative mechanisms for the formation and growth of vacancy clusters under the subthreshold irradiation mode. The simulation results are compared with experimental data, and ways of improving the model are discussed in order to explain the deuterium-saturation effect for high fluences (more than 1023 m−2)

Vacancy concentration in electron irradiated Ni3Al

A

On the thermal stability of late blooming phases in reactor pressure vessel steels: an atomistic study

Radiation-induced embrittlement of bainitic steels is the lifetime limiting factor of reactor pressure vessels in existing nuclear light water reactors. The primary mechanism of embrittlement is the obstruction of dislocation motion produced by nanometric defect structures that develop in the bulk of the material due to irradiation. In view of improving the predictive capability of existing models it is necessary to understand better the mechanisms leading to the formation of these defects, amongst which the so-called "late blooming phases". In this work we study the stability of the latter by means of density functional theory (DFT) calculations and Monte Carlo simulations based on a here developed quaternary FeCuNiMn interatomic potential. The potential is based on extensive DFT and experimental data. The reference DFT data on solute-solute interaction reveal that, while Mn-Ni pairs and triplets are unstable, larger clusters are kept together by attractive binding energy. The NiMnCu synergy is found to increase the temperature range of stability of solute atom precipitates in Fe significantly as compared to binary FeNi and FeMn alloys. This allows for thermodynamically stable phases close to reactor temperature, the range of stability being, however, very sensitive to composition. © 2013 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe