New understanding of one-dimensional thermal glide of a nano-sized prismatic dislocation loop in bcc iron: an atomic scale study

M Vijendran and R Matsumoto and S Taketomi, MATERIALS TODAY COMMUNICATIONS, 37, 107387 (2023).

DOI: 10.1016/j.mtcomm.2023.107387

Vacancy-type prismatic dislocation loops (PDLs) can be formed directly through cross-slip mechanisms of screw dislocations or via the accumulation and transformation of high-density vacancy-type defects. The concentration of vacancy-type defects in body-centered cubic (BCC) iron can be increased through plastic deformation and in the presence of hydrogen. Nano-sized PDLs can act as high-speed vacancy transport in BCC iron, causing embrittlement. Based on molecular dynamics simulations, this study comprehensively analyzes the onedimensional diffusion of vacancy-type PDLs composed of 37-169 vacancies (V37-V169) at temperatures ranging from 100 to 1000 K. The activation energy of diffusion increased with decreasing PDL size for small loops (V37-V61) but remained almost constant for larger loops (>V91). This behavior was found to be associated with the tensile stress produced by the opposing edge dislocation segment in the loop where the distance is closer for a smaller PDL. That is, the tensile stress along the slip direction of edge dislocation causes the unstable stacking fault energy to increase, and the change of dislocation core structure further contributes to an increase in the activation energy for the diffusion of PDL. In contrast, an external compressive stress reduces the activation energy and pre- exponential factor of diffusion in small PDLs, as exemplified in V37 PDL.

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