Dislocation behavior in nickel and iron during laser shock-induced plastic deformation

Laser shock peening is one of the most effective surface strengthening techniques, which uses laser shock-induced plastic deformation to optimize surface stress state and microstructures of target material. In this paper, dislocation dynamics simulation was used to investigate laser shock induced ultra-high strain rate plastic deformation of face-centered cubic (FCC) nickel and body-centered cubic (BCC) iron. Molecular dynamics was employed to calculate dislocation mobility. Based on the obtained dislocation mobility coefficient, dislocation dynamics models of nickel and iron were established. Results show that the velocity of dislocation motion increases as temperature decreases. Under ultra-high strain rate deformation, dislocation density of nickel increases while dislocation density of iron decreases as temperature rises. Moreover, iron exhibits thermal softening while nickel exhibits thermal hardening under laser shock loading. Plastic deformation dominated by dislocations is sensitive to loading direction, depending on the Schmidt factor of the slip system. The ultra-high strain rate induced by laser shock can effectively increase dislocation density by promoting dislocation multiplication and suppressing dislocation annihilation.