Cascade overlap with vacancy-type defects in Fe

Abstract

In order to understand the effect of irradiation on the material properties, we need to look into the atomistic evolution of the system during the recoil event. The nanoscale features formed due to irradiation will ultimately affect the macroscopic properties of the material. The defect production in pristine materials have been subject to investigation previously, but as the dose increases, overlap will start to happen. This effect of cascades overlapping with pre-existing debris has only recently been touched, and mainly been investigated for interstitial-type defects. We focus on vacancy-type defect clusters in BCC Fe and start a recoil event in their near vicinity. The final defect number as well as the transformation of the defect clusters are investigated, and their behaviour is related to the distance between the defect and the cascade centre. We found that for vacancy-type defects, the suppression of defect production is not as strong as previously observed for interstitial-type defects. The cascade-induced transformation, such as change in Burgers vector or creation of dislocations, was determined for all initial defect structures.

Microscopic structure of a heavily irradiated material

“…The multiple overlap cascade simulations by Granberg, Nordlund et al Refs. [24,81], carried out using the Fe potential by Mendelev, provide defect evolution data up to 0.16 NRT-DPA. Figure 13 plots the interstitial percentage versus cDPA arising from the early stages of Frenkel pair insertions along with scaled data originating from the cascade overlap simulations using the same empirical potential.…”

“…Simulations primarily explore the production of defects by impacts of energetic particle in the bulk of perfect crystals [17,18] or near surfaces [19,20]. Following the pioneering studies by Samaras et al [21,22], who analyzed how defects were produced by energetic collision events in nanocrystalline materials, extensive computer simulations have been performed exploring the effect of vacancy clusters [23,24], dislocations [25,26], dislocation loops [27], and grain boundaries [28] on defect production and accumulation in materials where the initial microstructure was different from the ideal periodic crystal lattice. Direct experimental observations show that the characteristic timescales of evolution of microstructure under irradiation depend strongly on the type of microstructure already present in the material.…”

Effect of cascade overlap and C15 clusters on the damage evolution in Fe: An OKMC study

“…This paper describes the interaction between cascades and pre-existing interstitial-type clusters. The effect of cascade overlap with vacancy-type defect clusters was not included in this study, as the effect was found to not be as considerable as for interstitial-type clusters [16]. The number of new Frenkel pairs (FPs) created in the close vicinity of a pre-existing cluster was presented by an analytical model [15].…”

“…change the Burgers vector of a dislocation loop [17]. In the same studies for iron, it was shown that the effect of interaction between cascades and pre-existing vacancy type clusters was not as significant [16].…”

“…In iron and tungsten this interaction has been investigated in several studies [15,16,31]. It was found that the effect of a collision cascade in the vicinity of pre-existing defects and defect clusters will depend on the separation distance between them.…”