Atomistic simulation of tiny glide loops in FCC Ni

Abstract

Experimental evidence suggests that dislocation formation is abrupt in initially dislocation free crystals. Models that account for the abruptness in the formation of dislocations (nucleation rather than multiplication) have been put forth by Khantha et al. and a simplified version by Sun et al. Both models consider the collective nucleation of tiny glide dislocation loops on a particular glide plane. Crucial to quantifying these models is an expression for the self energy of glide loops. Both models consider continuum expressions for the self energy of loops with radii ranging between 1--10b, where b is the Burgers vector of loops. At these small sizes of loops, core energy dominates the self energy of loops and atomistic techniques are required for a proper determination of the self energy. In this manuscript, an atomistic technique is presented for the determination of self energy of loops. Initially stresses required to equilibrate differently sized loops is determined atomistically. Such stresses are then integrated over the area of the loops to obtain the self energy of the loops. The technique is very similar to the atomistic technique used in determining the formation energy of kinks on dislocations. The atomistic technique is used in determining the selfmore » energy of loops with radii ranging between 1.5--10b in FCC Ni using an embedded atom method (EAM) potential developed for FCC Ni. It is shown that the atomistic results can be reasonably well fitted to the classical continuum expressions for self energy even at these small sizes of loops and glide loops with radii < 3b are expected to take part in the collective nucleation process in FCC Ni.« less