Effects of atomic grain boundary structures on primary radiation damage in α-Fe

Irradiation deformation near different atomic grain boundaries in α-Zr: An investigation of thermodynamics and kinetics of point defects

“…The atomic coordinates for the grain boundary structures are generated using GB studio 48 . In order to release stress in the GB structures, we have used steepest descent minimization method 39 40 under zero external pressure to obtain the minimum energy configurations of four GB structures considered here, as shown in Fig. 1 .…”

“…For MD simulations, we have used the same method proposed in our previous report in 40 that includes a block with slab geometry. To simulate and study the behavior of primary damage cascades, two systems are constructed 34 35 36 37 38 39 40 42 44 . The large system consisting of 642784–687452 atoms with a size of about ~241.3 × 242.2 × 264.9 Å 3 is used for simulating the primary radiation damage in Zr with GBs.…”

“…Periodic boundary conditions are applied in the directions parallel to the GB plane, and a fixed boundary condition in the direction normal to the GB plane 40 . In this configuration, the free atoms are sandwiched between two slabs of fixed atoms on each side of the GB plane 39 40 53 . Since the fixed boundary condition is applied in the direction normal to the GB, the size of the system in this direction is chosen to avoid interactions between the fixed boundary and the primary cascade 40 53 .…”

“…An atom, at different distances from the GB plane, is chosen as the PKA with 3, 6 and 9 keV of kinetic energy, directed perpendicularly towards the GB 39 40 53 . The final damaged structure is compared to the undamaged GB structure relaxed at 300 K (the reference system) to characterize defects, using the Wigner-Seitz (WS) cell method 39 40 53 . In the WS method, the whole system is divided into polyhedral WS cells centered on lattice sites.…”

“…Samaras et al 37 38 showed that the GBs in nano-crystalline face-centered cubic ( fcc ) and body-centered cubic ( bcc ) structures act as sinks for self-interstitial atoms (SIA), and deduced that for fcc Ni the absorption of interstitials leads to increasing production of stacking-fault tetrahedral, which they related to the dislocation structure of the GBs. Feghhi et al investigated the influence of atomic GBs on the energetic and kinetic properties of defects in bcc Fe 39 and fcc Ni 40 , and reported substantially large reduction of the defect formation energy and vacancy migration barrier in the neighboring region of the GBs, which they considered as the driving forces to observe biased absorption of interstitials over vacancies 39 40 . Tooq et al 41 studied defects evolution in fcc Ni with different GB structures and determined that the trapped vacancies in grain interiors had a tendency to cluster, and were immobile on picosecond (ps) timescale.…”