Effect of Mn addition on one-dimensional migration of dislocation loops in body-centered cubic Fe

Elucidation of the one-dimensional (1-D) motion of dislocation loops is important for describing the microstructural development of materials under irradiation. In this study, the effect of Mn on radiation-induced microstructure evolution in body-centered cubic Fe was experimentally investigated by focusing on the migration of dislocation loops. Pure Fe and Fe–1.4Mn alloy were irradiated with Fe3+ ions to introduce dislocation loops. In pure Fe, inhomogeneous distribution of loops in the vicinity of the residual dislocation was observed. However, in Fe–1.4Mn, isolated dislocation loops were homogeneously distributed in a high number density. In situ transmission electron microscopy during annealing revealed that 1-D motion of dislocation loops occurred in pure Fe at 623 K, while 1-D motion of dislocation loops occurred minimally in Fe–1.4Mn annealed at temperatures below 773 K. These results indicate that 1-D motion of dislocation loops play a key role in producing the differences in the microstructures between pure Fe and Fe–1.4Mn. In pure Fe, dislocation loops were mobile and trapped in the strain field of a dislocation, leading to the formation of loop decoration of dislocations. However, in Fe–1.4Mn, dislocation loops were less mobile and dislocation loops were homogeneously formed in high density in the matrix. The migration of dislocation loops by Mn solute is strongly suggested as one of the key mechanisms of microstructure development in irradiated Fe–Mn alloy.