Comprehensive study of vacancy frank loop unfaulting: atomistic simulations and predictive model

Abstract In this study, vacancy Frank loop unfaulting via Shockley partial loop(s) in two model material systems (Al and Ni) has been investigated through comprehensive atomistic simulations combining continuum modeling. A general approach has been outlined and has been demonstrated to enable reliable construction of different dislocation loop configurations. The unfaulting of vacancy Frank loop is shown to occur when the enclosed Shockley loop exceeds a threshold size, independent of the Frank loop radius. A continuum model is then established to quantitatively predict the geometrical parameters of the Shockley loop and threshold condition for unfaulting. The continuum model prediction yields excellent agreement with simulation results, and has been shown to apply in various different unfaulting scenarios involving either single or multiple Shockley loops. Experimentally observed Butterfly and Mercedes hexagon morphologies have been reproduced from our simulations, with the underlying dislocation reactions fully clarified, and a mechanism of competitive growth identified as the cause for their subsequent transformation into normal prismatic dislocation loops. The present study offers generic and flexible computational tools towards understanding defect reactions and evolution mechanism of Frank loops, and more generally secondary defects in quenched and irradiated materials.