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

Molecular dynamics (MD) modelling has been employed to investigate the effe ct 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 alpha -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 fashio n to that simulated at 100 K, but it is reduced further and saturates at ab out 20% over the energy range considered at 600 K. The number and size of c lusters, both vacancy and interstitial, are increased by increasing PKA ene rgy, and the fraction of interstitials in clusters also increases with incr easing lattice temperature. The interstitial clusters can glide back and fo rth 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 interstitial s and some small clusters can migrate along both < 11 (2) over bar0 > and < (2) over bar 203 > directions at 600 K. Clusters containing up to 25 inters titials and 24 vacancies were formed by 20 keV cascades at 600 K, and almos t all of the clusters have the form of a dislocation loop with Burgers vect or 1/3 < 11 (2) over bar0 >. It was found that the 25-interstitial cluster is glissile and dissociates on the basal and prism-planes that form its gli de cylinder. Collapse of the 24-vacancy cluster to a perfect vacancy disloc ation loop was found to occur in the primary damage process due to the long er lifetime of the thermal spike at higher temperature. The results are dis cussed in terms of experimental data and compared with those simulated at 1 00 K. (C) 2001 Published by Elsevier Science B.V.