Point-defect clusters and dislocation loops in bcc metals: Continuum and atomistic study

Linear elasticity theory and atomistic computer modelling were applied to study properties such as the formation energy, stress and displacement field for planar clusters of point defects and small dislocation loops. Two different interatomic potentials have been used to simulate perfect vacancy and interstitial clusters up to 6 nm in diameter in a {111} plane in a model of bcc Fe. The accuracy of the continuum description of formation energy, stress and displacement field depends on the cluster or loop size and the distance from its edge; it is better for large loops at large distance. However, even for the largest defect studied, the stress distribution, especially that inside the glide prism, calculated from the atomistic model is significantly wider than that estimated by elasticity theory. The difference between planar clusters of point defects and dislocation loops and the limitations of the linear elasticity description are discussed. It is concluded that clusters of up to about 2 nm in diameter cannot be described as dislocation loops in the isotropic continuum approach.