Abnormal growth of loops by repulsive interaction between loops and dislocations

Abstract

Pre-existing dislocations have a significant impact on the evolution of radiation defects, which in turn affect the mechanical properties of materials after irradiation. However, systematic research into the question of how pre-existing dislocations affect the evolution of defects is essential and has yet to be carried out. In this work, the effect of pre-existing dislocations on loop evolution in FeCrAl alloys is investigated by in-situ transmission electron microscopy (TEM) using Fe⁺+He⁺+H₂⁺ tri-beam irradiation. It is found that the dislocations exhibit a strong sink effect and the values of the number density and size of the dislocation loops are lower in regions with pre-existing dislocations. As the calculation of sink strength shows, the sink effect of dislocations can be weakened due to the initiation of dislocation gliding, by the absorption of point defects and by climbing. And this impaired sink effect is the main reasons for the formation of a V-shaped density profile. A coexisting repulsive interaction between loops and dislocations has been proposed, which also has an important effect on the evolution morphology of loops, and its validity has been demonstrated by the interaction energy calculations. The repulsive interaction of dislocations pushes the defects away, leading to a higher probability of nucleation and coalescence. This can lead to a greater number and abnormally rapid growth of loops. In addition, a stronger surface effect is found for the thinner foil, where the density is lower and the size is smaller. The finger-shaped loops are found to be absent in the thinner samples due to the annihilation of the large loops.