Point defect dynamics in bcc metals

TL;DR

This paper analyzes the evolution of point defect populations in bcc metals under irradiation, comparing rate equations and kinetic Monte Carlo models, revealing growth patterns and defect distributions.

Contribution

It introduces a combined rate equation and kMC approach to model defect dynamics, highlighting the impact of migration rate disparities and cluster behaviors in bcc metals.

Findings

Vacancy population grows as the square root of time due to migration rate mismatch.

Vacancy cluster size distribution follows an exponential function.

Model applied to vanadium and alpha-iron with relevant parameters.

Abstract

We present an analysis of the time evolution of self-interstitial atom and vacancy (point defect) populations in pure bcc metals under constant irradiation flux conditions. Mean-field rate equations are developed in parallel to a kinetic Monte Carlo (kMC) model. When only considering the elementary processes of defect production, defect migration, recombination and absorption at sinks, the kMC model and rate equations are shown to be equivalent and the time evolution of the point defect populations is analyzed using simple scaling arguments. We show that the typically large mismatch of the rates of interstitial and vacancy migration in bcc metals can lead to a vacancy population that grows as the square root of time. The vacancy cluster size distribution under both irreversible and reversible attachment can be described by a simple exponential function. We also consider the effect of highly mobile interstitial clusters and apply the model with parameters appropriate for vanadium and $\alpha-$iron.