| Abstract Scope |
Experimental evidence indicates that substantial concentrations of self-interstitial atom (SIA) dislocation loops develop in the microstructure of irradiated metals, obstructing dislocation motion and contributing to irradiation embrittlement. However, the mechanisms for dislocation loop migration and coalescence are not fully understood. In particular, a<100> SIA loops in bcc Fe are commonly observed at irradiation temperatures exceeding around 500 °C and have been observed to coalesce with neighboring loops and exit through free surfaces. The role of dislocation glide in the migration of these loops has been questioned, as most existing molecular dynamics (MD) calculations using conventional semiempirical potentials suggest that they are essentially sessile. Though, the emergence of machine-learned interatomic potentials (MLPs), which are generally regarded as a better representation of the quantum force field of a material than conventional potentials, motivates a reexamination of SIA loop glide mechanisms.
To examine the glide mobility of a<100> SIA loops in bcc Fe, atomistic simulations are conducted utilizing multiple highly accurate MLPs. Possible axial loop migration mechanisms are sampled using MD and the corresponding energy barriers are determined with nudged elastic band computations. Loop motion is mainly through kink pair glide for which the energetic barriers could be feasibly supplied by thermal energy at temperatures where a<100> SIA loops are commonly observed, around 500 °C. This work demonstrates that dislocation glide is a competitive mechanism for the migration of a<100> SIA loops in bcc Fe, which has important implications for predicting the long-term microstructural evolution of irradiated Fe. |