Hardening by completely and partially absorbed ½<111> and <100> dislocation loops reacting with dislocations in α-Fe.

Molecular dynamics simulations were used to investigate reactions between an ½<111>{110} edge dislocation with interstitial dislocation loops with Burgers vector equal to either ½111 or 100. The loop size was varied from 0.5 nm up to 8.6 nm, and simulations of both static and dynamic conditions were performed. The results obtained show that small loops (with size up to ~1nm) are easily absorbed by reaction with edge dislocations, independently of their Burgers vector. Large loops are strong obstacles and, depending on the difference in orientation of the dislocation and loop Burgers vectors, are either completely or partially absorbed. The mechanism that provides complete absorption of relatively large loops involves propagation of the reaction segment, formed in favourable dislocation reaction, over the loop surface. This motion is controlled by cross-slip of the screw dislocations formed in a dipole and can involve complicated dislocation reactions. Thus, thermally-activated glide and/or decomposition of the pinning segment formed in the favourable reaction determines both the absorption and critical stress, and therefore depends on temperature, strain rate and loop size.