Computer simulation of primary damage creation in displacement cascades in copper. I. Defect creation and cluster statistics

Abstract

Atomic-scale computer simulation has been used to investigate the primary damage created by displacement cascades in copper over a wide range of temperature (100K⩽T⩽900K) and primary knock-on atom energy (5keV⩽EPKA⩽25keV). A technique was introduced to improve computational efficiency and at least 20 cascades for each (EPKA,T) pair were simulated in order to provide statistical reliability of the results. The total of almost 450 simulated cascades is the largest yet reported for this metal. The mean number of surviving point defects per cascade is only 15–20% of the NRT model value. It decreases with increasing T at fixed EPKA and is proportional to (EPKA)1.1 at fixed T. A high proportion (60–80%) of self-interstitial atoms (SIAs) form clusters during the cascade process. The proportion of clustered vacancies is smaller and sensitive to T, falling from 30% to 60% for T⩽600K to less than 20% when T=900K. The structure of clusters has been examined in detail. Vacancies cluster predominantly in stacking-fault-tetrahedron-type configurations. SIAs tend to form either glissile dislocation loops with Burgers vector b=1/2<110> or sessile faulted Frank loops with b=1/3<111>. Despite the fact that cascades at a given EPKA and T exhibit a wide range of defect numbers and clustered fractions, there appears to be a correlation in the formation of vacancy clusters and SIA clusters in the same cascade. The size and spatial aspects of this are analysed in detail in part II [unpublished], where the stability of clusters when another cascade overlaps them is also investigated.