A new mechanism of loop formation and transformation in bcc iron without dislocation reaction

Structure and kinetics of dislocation loops in α-Fe is an active field in material science, due to their implications on fundamental understanding as well as application of structural materials in irradiation environments. Recent computer simulations provoke new conceptions, which call for experimental verification. The present investigation reports transmission electron microscopy of small interstitial dislocation loops (2.5–10 nm diameters) in bcc iron, irradiated with 25 MeV α-particles at 573 K up to 0.13 dpa. The observed 〈1 0 0〉 and ½〈1 1 1〉 loops have habit planes of (1 0 0), and (1 1 0), (1 1 1) and (2 1 1), respectively. Furthermore it is observed that loops also contain ½〈1 1 1〉{2 1 1} and 〈1 0 0〉{1 0 0} components which are considered as intermediate stages of transformation of ½〈1 1 1〉 loops to 〈1 0 0〉. Based on these observations, a new mechanism of loop formation and transformation by self-interstitial atoms aggregation is proposed, with concurrent molecular dynamic simulations supporting the kinetic feasibility of the proposed process.