Atomistic simulations of irradiation damage on the engineering timescale: Examining the dose rate effect in tungsten

TL;DR

This paper introduces an accelerated atomistic simulation method to study irradiation damage in tungsten over realistic timescales, revealing how dose rate and temperature influence defect evolution and void formation.

Contribution

The authors develop a parameter-free atomistic simulation approach that accelerates vacancy motion, enabling prediction of microstructural evolution under irradiation at elevated temperatures.

Findings

Higher temperature or lower dose rate reduces steady-state defect concentration.

Nanoscale void formation occurs with large dislocation loops under irradiation.

A simple rate theory model matches simulation defect dynamics.

Abstract

The change in materials properties subjected to irradiation by highly energetic particles strongly depends on the irradiation dose rate. Atomistic simulations can in principle be used to predict microstructural evolution where experimental data is sparse or unavailable, however, fundamental limitations of the method make it infeasible to replicate the experimental timescale spanning from seconds to hours. Here, we present an atomistic simulation method where the motion of vacancies is accelerated, while the fast degrees of freedom are propagated with standard molecular dynamics. The resulting method is free of adjustable parameters and can predict microstructural evolution under irradiation at elevated temperatures. Simulating the microstructural evolution of tungsten under irradiation at dose rates of $10^{-5}$, $10^{-4}$, and $10^{-3}$ dpa/second, we find that increasing the temperature or reducing the dose rate primarily results in a reduction of the steady-state defect concentration, in qualitative agreement with deuterium retention and post-irradiation resistivity recovery experiments. The formation of a nanoscale void is observed if a system initially containing a large dislocation loop is irradiated. We present a minimally simple rate theory model which reproduces the time-dependent defect concentration and volume swelling behaviour obtained from the simulations.