Atomistic modeling of long-term evolution of twist boundaries under vacancy supersaturation

E Martinez and A Caro, PHYSICAL REVIEW B, 86, 214109 (2012).

DOI: 10.1103/PhysRevB.86.214109

Vacancy accumulation in 4 degrees 110 bcc Fe and 2 degrees 111 fcc Cu twist boundaries (TBs) has been studied. These interfaces are characterized by different sets of screw dislocations: two sets of a(0)/2 < 111 > and one set of a(0)/2 < 100 > in Fe and three sets of a(0)/6 < 112 > in Cu. We observe that vacancies agglomerate preferentially at the misfit dislocation intersections (MDIs), where their formation energy is lower. In bcc the dislocation structure remains stable, but in fcc the interface rearranges itself increasing the stacking fault area. To perform this study a kinetic Monte Carlo algorithm coupled with the molecular dynamics code LAMMPS has been developed. Atomic positions are relaxed at every step after an event takes place to account for long-range strain fields. The events considered in this work are vacancy migration hops. The rates are calculated via harmonic transition state theory with the energy at the saddle point obtained either by a linear approximation considering the relaxed energy of the initial and final configurations or the nudged- elastic band method depending on the vacancy position in the sample. Vacancy diffusivities at both interfaces have also been calculated. For the 110 TB in Fe the diffusivity is of the same order of magnitude as in bulk (D-TB(Fe) = 2.60 x 10(-13) m(2)/s) while at the 111 TB in Cu, diffusivities are two orders of magnitude larger than in bulk (D-TB(Cu) = 2.06 x 10(-12) m(2)/s). The correlation factors at both interfaces are extremely low (f(TB)(Fe) = 1.61 x 10(-4) and f(TB)(Cu) = 3.34 x 10(-4)), highlighting the importance of trapping sites at these interfaces. DOI: 10.1103/PhysRevB.86.214109

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