Displacement cascades and defects annealing in tungsten, Part I: defect database from molecular dynamics simulations

TL;DR

This study uses molecular dynamics to create a detailed database of defect formation in tungsten due to displacement cascades, revealing energy-dependent regimes, defect clustering behaviors, and temperature effects on defect types and sizes.

Contribution

It provides the first comprehensive database of defect production in tungsten across a wide energy and temperature range, highlighting new defect clustering and formation behaviors.

Findings

Two regimes of defect production with distinct power-law exponents.

Transition energy at approximately 250×E_d marks a change in defect behavior.

Temperature influences defect clustering, increasing SIA clusters and reducing vacancy clusters.

Abstract

Molecular dynamics simulations have been used to generate a comprehensive database of surviving defects due to displacement cascades in bulk tungsten. Twenty one data points of primary knock-on atom (PKA) energies ranging from 100 eV (sub-threshold energy) to 100 keV ($\sim$780$\times E_d$, where $E_d$ is the average displacement threshold energy) have been completed at 300 K, 1025 K and 2050 K. Within this range of PKA energies, two regimes of power-law energy-dependence of the defect production are observed. A distinct power-law exponent characterizes the number of Frenkel pairs produced within each regime. The two regimes intersect at a transition energy which occurs at approximately 250$\times E_d$. The transition energy also marks the onset of the formation of large self-interstitial atom (SIAs) clusters (size 14 or more). The observed defect clustering behavior is asymmetric, with SIA clustering increasing with temperature, while the vacancy clustering decreases. This asymmetry increases with temperature such that at 2050 K ($\sim 0.5 T_m$) practically no large vacancy clusters are formed, meanwhile large SIA clusters appear in all simulations. The implication of such asymmetry on the long-term defect survival and damage accumulation is discussed. In addition, rare $<$100$>${110} SIA loops are observed.