Role of thermal spikes in energetic displacement cascades

Abstract

The role of thermal spikes in energetic displacement cascades has been investigated by moleculardynamics computer simulation. For cascade energies of 3 and 5 keV in Cu, which are the highest energies (in reduced units) yet treated by fully dynamical simulations, it is found that local melting occurs and persists for several picoseconds. The implications of this behavior for atomic mixing, Frenkel-pair production, and point-defect clustering are discussed.

Mechanisms of Defect Production and Atomic Mixing in High Energy Displacement Cascades: A Molecular Dynamics Study

“…Although pair potential studies of 5 keV cascades in Cu and Ni [9][10][11] provided extensive evidence for vacancy clustering, the results of this work are the first theoretical confirmation of experimental results that show cascade collapse to vacancy dislocation loops at ambient temperature below annealing stage I.…”

“…argely confirmed previc s 5 keV results with pair potentials regarding the ejection of SIAs by RCSs from the molten core of the cascade. A]so, the previously observed clustering of small numbers of SIAs as the result of the elastic interaction among SIAs ejected from the cascade core via RCSs [9] has been confirmed. These studies have also provided statistically significant information on the absolute number of defects produced in low energy cascades in Cu.…”

“…Previous MD studies of 5 keV displacement cascades in Cu and Ni [9][10][11] with pair potentials showed that local melting takes place at the core of the cascade. It was concluded that the melting point is the physical quantity that determines the behavior of a metal under cascade-producing irradiation.…”

“…Previous MO studies, as well as the cascades described here, have shown that the large elastic interaction of SIAs may lead to clustering of RCSs ejected from the cascade core. Evidence for this process has been presented before [9] and is also depicted in figure 9 where the replacement "cloud" (i.e., all the lattice sites in which an atomic replacement has taken place during the lifetime of the cascade) resulting from a 5 keV PKA event is shown. Clearly visible ara RCS trails leading to SIAs that are well separated from the edge of the disorder region.…”

“…The recent surge in the availability and power of supercomputers has made the use of MD plausible for radiation damage studies at higher energy. MD studies of 5 keV cascades in Cu and Ni with pair potentials led to a model of formation of the primary state of radiation damage in metals based on the concept of local melting during the thermal spike [9][10][11]. Within this simple "liquid droplet" model, defect production, point defect clustering and the amount of atomic rearrangement produced in a displacement cascade {i.e., ion beam mixing) are all governed by the extent and lifetime of the melt zone and therefore by the melting behavior of the material under study.…”