Temperature-dependence of defect creation and clustering by displacement cascades in α-zirconium

Molecular dynamics (MD) modelling has been employed to investigate the effect of lattice temperature on the production of vacancies and interstitials in the primary damage process of displacement cascades with energy up to 20 keV in α-zirconium. The final number of Frenkel pairs decreases with increasing temperature due to the increase in lifetime of the thermal spike at high temperature. The production efficiency behaves in a similar fashion to that simulated at 100 K, but it is reduced further and saturates at about 20% over the energy range considered at 600 K. The number and size of clusters, both vacancy and interstitial, are increased by increasing PKA energy, and the fraction of interstitials in clusters also increases with increasing lattice temperature. The interstitial clusters can glide back and forth by one-dimensional migration along the crowdion direction at 100 K, but small clusters of less than four SIAs can change their glide direction on and off basal-planes at 600 K. It is also observed that single interstitials and some small clusters can migrate along both <1 1 2-bar 0> and <2-bar 2 0 3> directions at 600 K. Clusters containing up to 25 interstitials and 24 vacancies were formed by 20 keV cascades at 600 K, and almost all of the clusters have the form of a dislocation loop with Burgers vector 1/3<1 1 2-bar 0>. It was found that the 25-interstitial cluster is glissile and dissociates on the basal and prism-planes that form its glide cylinder. Collapse of the 24-vacancy cluster to a perfect vacancy dislocation loop was found to occur in the primary damage process due to the longer lifetime of the thermal spike at higher temperature. The results are discussed in terms of experimental data and compared with those simulated at 100 K