Atomistic simulations of athermal irradiation creep and swelling of copper and tungsten in the high dose limit

TL;DR

This study uses atomistic simulations to explore how copper and tungsten deform and swell under high-dose irradiation, revealing stress-dependent anisotropic deformation and developing a faster modeling algorithm for high-dose microstructures.

Contribution

The paper introduces a novel, efficient algorithm for modeling high-dose irradiation microstructures, capturing defect evolution with reduced computational cost.

Findings

Copper and tungsten respond similarly to irradiation despite different crystal structures.

Irradiation causes stress-dependent anisotropic deformation aligned with applied stress.

High-dose irradiation results in greater swelling and defect content compared to low-dose irradiation.

Abstract

Radiation creep and swelling are irreversible deformation phenomena occurring in materials irradiated even at low temperatures. On the microscopic scale, energetic particles initiate collision cascades, generating and eliminating defects that then interact and coalesce in the presence of internal and external stress. We investigate how copper and tungsten swell and deform under various applied stress states in the low- and high-energy irradiation limits. Simulations show that the two metals respond in a qualitatively similar manner, in a remarkable deviation from the fundamentally different low-temperature plastic behaviour of bcc and fcc. The deviatoric part of plastic strain is particularly sensitive to applied stress, leading to anisotropic dimensional changes. At the same time, the volume change, vacancy content and dislocation density are almost insensitive to the applied stress. Low- as opposed to high-energy irradiation gives rise to greater swelling, faster creep, and higher defect content for the same dose. Simulations show that even at low temperatures, where thermal creep is absent, irradiation results in a stress-dependent irreversible anisotropic deformation of considerable magnitude, with the orientation aligned with the orientation of applied stress. To model the high dose microstructures, we develop an algorithm that at the cost of about 25% overestimation of the defect content is up to ten times faster than collision cascade simulations. The direct time integration of equations of motion of atoms in cascades is replaced by the minimisation of energy of molten spherical regions; multiple insertion of molten zones and the subsequent relaxation steps simulate the increasing radiation exposure.