Slow relaxation of cascade-induced defects in Fe

Abstract

On-the-fly kinetic Monte Carlo simulations are performed to investigate slow relaxation of nonequilibrium systems. Point defects induced by 25 keV cascades in $\ensuremath{\alpha}$-Fe are shown to lead to a characteristic time evolution, described by the replenish-and-relax mechanism. Then, we produce an atomistically based assessment of models proposed to explain the slow structural relaxation by focusing on the aggregation of 50 vacancies and 25 self-interstitial atoms in 10-lattice-parameter $\ensuremath{\alpha}$-Fe boxes, two processes that are closely related to cascade annealing and exhibit similar time signatures. Four atomistic effects explain the time scales involved in the evolution: defect concentration heterogeneities, concentration-enhanced mobility, cluster-size-dependent bonding energies, and defect-induced pressure. These findings suggest that the two main classes of models to explain slow structural relaxation, the Eyring model and the Gibbs model, both play a role in limiting the rate of relaxation of these simple point-defect systems.