Reactions between a 1/2⟨111⟩ screw dislocation and ⟨100⟩ interstitial dislocation loops in alpha-iron modelled at atomic scale

Abstract

Interstitial dislocation loops with Burgers vector of type are observed in α-iron irradiated by neutrons or heavy ions, and their population increases with increasing temperature. Their effect on motion of a edge dislocation was reported earlier 1. Results are presented of a molecular dynamics study of interactions between a screw dislocation and loops in iron at temperature in the range 100 to 600 K. A variety of reaction mechanisms and outcomes are observed and classified in terms of the resulting dislocation configuration and the maximum stress required for the dislocation to break away. The highest obstacle resistance arises when the loop is absorbed to form a helical turn on the screw dislocation line, for the dislocation cannot glide away until the turn closes and a loop is released with the same Burgers vector as the line. Other than one situation found, in which no dislocation–loop reaction occurs, the weakest obstacle strength is found when the original loop is restored at the end of the reaction. The important role of the cross-slip and the influence of model boundary conditions are emphasised and demonstrated by examples.

Keywords:

• iron
• neutron irradiation damage
• interstitial dislocation loops
• screw dislocation
• dislocation–loop interaction
• molecular dynamics
• strengthening mechanism

Acknowledgements

This work was carried out within the framework of the European Fusion Development Agreement (EFDA). It was also supported by grant GR/S81162/01 from the UK Engineering and Physical Sciences Research Council; grant F160-CT-2003-508840 (‘PERFECT’) under programme EURATOM FP-6 of the European Commission; and partly by the Division of Materials Sciences and Engineering and the Office of Fusion Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. DT thanks EDF for use of high performance computing facilities.