A manifestation of antisite defects created by nuclear irradiation in binary ordered alloys is investigated. Calculations show that the concentration of such defects can be large at typical values of intensity of irradiation and temperature. The appearance of structural defects can cause the time and space instabilities in crystal during irradiation. Time instabilities are connected with the acceleration of antisite defect relaxation due to the heat that is released during this relaxation. The instability leads to appearance of self-oscillations of defect density and temperature of crystal. Space instability arises due to interaction between defects created by irradiation. It leads to spatial periodical modulation of antisite defect density.

An approach is suggested for using pulsed irradiation experiments to study attributes of the transient sink formed by cascade producing radiation. As an example, a simple model of radiation enhanced diffusion is proposed for a dual ion beam irradiation in which one of the beams is a pulsed, sink-producing heavy ion. It is demonstrated that by combining this model with diffusivity measurements evaluated as a function of the irradiation pulse wavelength, it is possible to quantitatively determine the transient sink strength and its characteristic lifetime.

The results of molecular dynamics displacement cascade simulations in iron at energies up to 50 keV and temperatures of 100, 600, and 900K are summarized, with a focus on the characterization of interstitial and vacancy clusters that are formed directly within the cascade. The fraction of the surviving point defects contained in clusters, and the size distributions of these in-cascade clusters have been determined. Although the formation of true vacancy clusters appears to be inhibited in iron, a significant degree of vacancy site correlation was observed. These well correlated arrangements of vacancies can be considered nascent clusters, and they have been observed to coalesce during longer term Monte Carlo simulations which permit short range vacancy diffusion. Extensive interstitial clustering was observed. The temperature and cascade energy dependence of the cluster size distributions are discussed in terms of their relevance to microstructural evolution and mechanical property changes in irradiated iron-based alloys.

In order to describe the long term evolution of the defects produced by a displacement cascade, Molecular dynamics (MD) and Kinetic Monte Carlo (KMC) methods are employed. Using an empirical Ni interatomic potential in MD, the damage resulting from primary knock-on atom (PKA) energies up to 30 keV has been simulated. The annealing kinetics and the fraction of freely migrating defects (FMD) are determined for each single displacement cascade, by a KMC code which is based on a set of parameters extracted mainly from MD simulations. It allows an atomistic study of the evolution of the initial damage over a time scale up to lOOs and the determination of the fraction of the defects that escape the KMC box, compared to those obtained by MD, as function of temperature and PKA energy. It has been found that this fraction depends strongly on the temperature but reaches a saturation value above stage V.

The production bias model of radiation damage has focused attention on the production of glissile clusters (GCs) in the displacement cascades. The formation of glissile SIA clusters in molecular dynamics simulations of cascades has been reported frequently whereas information about sessile clusters (SCs) is rather sparse. Comprehensive models of microstructure evolution in metals under irradiation conditions should include all possible defects (and clusters) and interactions between them. Detailed information of this nature can be obtained by means of atomic-scale computer simulation. In the present paper we review some recent results of atomistic simulation of sessile and glissile defect clusters in metals, dealing with their mechanisms of formation and their properties. In particular, we discuss the formation of SCs and GCs in the cascade region and also their creation in bulk metal as a result of cluster growth.

Recent molecular dynamics (MD) computer simulations have shown that clusters consisting of up to a few tens of self-interstitial atoms (SIAs) are highly mobile along closed-packed crystallographic directions in pure copper and iron. This effect has important consequences for microstructure evolution in irradiated metals and so it is desirable to investigate the mechanisms of the cluster motion. In the present paper the results of MD modelling of the thermally-activated motion of clusters of 3, 9 and 17 SIAs in α-Fe in the temperature range from 90 to 1400 K are analyzed. The extensive MD data has enabled the migration of clusters, as well as that of individual SIAs in the clusters, to be treated with high statistical accuracy. The correlation between the motion of the centre of gravity of a cluster and the jumps of individual SIAs in the cluster is revealed. It is found that the SIAs in a cluster jump almost independently and their jump frequency depends on the number of SIAs in the cluster. This leads to a simple relationship between the jump frequency of a cluster and the number of SIAs in it. The cluster jump frequency exhibits a deviation from the Arrhenius relationship. The reason for this is discussed.

The mobile defects created in displacement cascades can either interact within the cascade region or undergo long-range diffusion in the crystal. The kinetic Monte Carlo code ALSOME has been used in the present work to carry out annealing simulations of electron irradiation and single cascades with energy in the range of 2 to 40 keV in α-Fe as a function of temperature. Isochronal annealing of electron irradiation shows a temperature-dependence of the recovery stages that is reasonably close to experiment, but Stage I is controlled by the rotation energy of the <110> dumbbell to the <111> crowdion. The annealing of single cascades has demonstrated that nearly 60% of SIAs formed in the primary state of cascade damage escape from the cascade at temperatures above stage I. Most of the escaping SlAs are in clusters, for only 10% of them are mono-interstitials. Although the number of escaping defects increases with increasing cascade energy, the relative fraction is almost constant for the recoil energies considered. The results are compared with those for copper obtained using the same code [1].

The Monte Carlo (MC) method is used to study cascade damage effects in damage accumulation in pure metals at temperatures below stage III, when vacancies and their clusters are immobile. The irradiation is modelled by sequential introduction of collections of defects representing the primary damage state of cascades placed randomly in the simulation volume. The cascades generated in molecular dynamics simulations for recoil energies from 2 to 20keV are used. Concentrations of point defects as well as defect cluster densities are monitored as a function of dose up to 0.02dpa. The results are compared with those obtained in the mean-field approximation. Factors responsible for the difference in damage accumulation under homogeneous and cascade irradiation conditions are revealed. The effects of temperature and recoil energy are studied. Problems in MC modelling of one-dimensional diffusion of interstitial clusters connected with the limited volume of the simulation box are revealed.

The ease with which ceramic structures amorphize under displacive radiation is considered from the point of view of connectivity and the consequent topological constraints which impose rigidity on the original atomic arrangement. These constraints define a measure of topological freedom to rearrange which has been shown previously to correlate with measured energy deposition density during ion-induced amorphization. That earlier assessment of topological freedoms is extended here to include more complex connectivities and is shown to be representable in an analytical form which reflects the progressive destruction of topological constraints.