Defect Cluster Formation in High Energy Displacement Cascades in Copper
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Defect Cluster Formation in High Energy Displacement Cascades in Copper Yuri N. Osetsky and David J. Bacon Materials Science and Engineering, Department of Engineering, The University of Liverpool, Brownlow Hill, Liverpool L69 3GH, UK.
ABSTRACT Primary radiation damage in displacement cascades in metals has been studied extensively by atomistic simulation during the last decade. The variety of defect types observed in cascade simulation is not entirely consistent with experimental data. For example, experiments on copper show a very effective production of stacking fault tetrahedra (SFTs) but this was not observed systematically in cascade simulation. To clarify this and related issues, extensive simulation of displacement cascades in copper have been performed using two different interatomic potentials, a short-range many-body potential and a long-range pair potential. We have studied the damage created by primary knock-on-atoms of energy up to 20keV, i.e. below the energy range for formation of subcascades, at temperatures 100 and 600K. Special attention was paid to cascade statistics and the accuracy of simulation in the collision stage. The former required many simulations for each temperature whereas the latter involved a modification of the simulation method. The results on variety of clusters observed, e.g. SFTs, glissile and sessile interstitial clusters, and faulted and perfect interstitial dislocation loops, lead to conclusions on the effect of the potentials and the significant variation of the number of Frenkel pairs and clustering effects produced in different cascades under the same conditions. INTRODUCTION The displacement cascade is the principal source of damage during irradiation of metals by energetic atomic particles and has been the subject of intense study by computer simulation [1-4] and detailed knowledge of the primary damage state has been obtained for different metals. Further, the clustering of point defects in cascades has important consequences for microstructure evolution under cascade damage conditions [5]. However, there is a lack of variety of defect types observed in cascade simulation, which, in many cases, makes it difficult to explain experimental data. For example, low- and high-temperature experiments on copper show an efficient production of stacking fault tetrahedra (SFTs) [6] but they have not been observed systematically in cascade simulation [1,4]. This is rather surprising because simulations of the evolution of a hot, vacancy-rich zone have demonstrated an effective formation of an SFT under this condition [7,8]. Although SFTs are found to occur in simulation of surface irradiation [9], we are not aware of reports of SFT formation in modelling of the bulk. Because SFTs are an important element of microstructure in affecting mechanical properties, their creation under irradiation should be clarified. To investigate this, we have launched an in-depth study of cascades in copper, a typical fcc metal in which SFTs are observed. We use interatomic potentials of significantl
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