Microscopic structure of a heavily irradiated material

Abstract

It has been long hypothesized that the structure of a material bombarded by energetic particles might approach a certain asymptotic steady state in the limit of high exposure to irradiation. There is still no definitive verdict regarding the validity of this hypothesis or the conditions where it applies. To clarify this, we explore a highly simplified model for microstructural evolution that retains full atomic detail of the underlying crystal structure and involves random events of generation and relaxation of defects. We explore the dynamics of evolution of the model in the limit T = 0, where the defect and dislocation microstructure is driven purely by the spatially fluctuating stress field accumulating as a result of stochastic generation of point defects. Using body-centred cubic iron and tungsten as examples, we show that their microstructure exhibits a structural transition and then approaches a limiting asymptotic state at doses of order O(0.1) and O(1) canonical defects per atom, respectively, and analyze the microscopic and macroscopic parameters characterizing both the transition and the asymptotic microstructural state.

Nanoscale lattice strains in self-ion implanted tungsten

“…The mottled features have a size in the range of 20-70 nm, in some cases forming longer, chain-like features. Independent simulations of irradiation damage evolution have concurrently predicted that spatially fluctuating stress fields within an evolving cascade microstructure will influence the behaviour of subsequent cascades, resulting in the formation of complex damage microstructure with long range order evidenced as strong variations in stress and strain [64]. The measurements of strain heterogeneity presented here complement two-dimensional TEM observations of damage microstructure and provide, in three-dimensions, experimental verification of the predicted defect ordering at length scales considerably larger than those accessible via atomistic simulation.…”

Efficient and transferable machine learning potentials for the simulation of crystal defects in bcc Fe and W

“…In bcc metals, and in particular in Fe and W, the defect energy landscape is very complex [70,73]. Both metals accommodate a rich morphology of defects with size-dependent stability and mobility.…”

“…In this work we aim to design ML force fields that are suitable for modeling radiation-induced defects in Fe and W and allow performing large-scale calculations. The energy landscape of defects in bcc Fe and W is extremely complex [65][66][67][68][69][70][71][72][73] and its accurate description at the atomic scale requires using appropriate force-field models that provide a correct description of atomic systems beyond the equilibrium conditions. The new potentials should have higher accuracy than traditional potentials for the essential properties of defects and, in addition to that, correctly reproduce the peculiar behavior of some small defects known from ab initio calculations, such as negative binding energy of the di-vacancies in W [74][75][76][77][78][79][80], the distinct energy landscape of C15 interstitial clusters in Fe [68,72,[81][82][83], dislocation core structures as well as the shape and the magnitude of the Peierls barrier [84][85][86][87].…”

Ultraviolet catastrophe of a fluctuating curved dislocation line

“…The general occurrence of fluctuations suggests that they represent the most fundamental aspect of dislocation-mediated deformation of metals, defining the nature of brittle-ductile transitions, hardening, fracture, and creep-in other words, the entire range of phenomena that determine the lifetime of engineering structures from an aircraft engine to a nuclear reactor. Fluctuations of dislocation lines also reflect the complex nature of the transition from discrete atoms to continuous fields in the treatment of the deformation of crystalline materials, representing the foundation of mathematical analyses of microstructure and mechanical properties [10][11][12][13].…”

“…The effective stress needed for computing the Peach-Koehler force [20,21] requires the convolved tensor of third derivatives, which is given in the Supplemental Material [32] along with the derivation of Eq. (13). Note that the single-convolved inverse distance, as required for evaluating elastic fields in the local core model, is obtained by setting η equal to the appropriate κ (i) in Eq.…”