Dissociation of a ⟨100⟩ edge superdislocations in the γ ′-phase of nickel-base superalloys

Abstract

Dissociation of a⟨100⟩ edge superdislocations in Ni3Al, the hardening γ′-phase of nickel-base superalloys, was investigated using molecular dynamics simulations and theory of elasticity. It was shown that these dislocations dissociate either symmetrically or asymmetrically when they are close to the ⟨011⟩ orientation. The symmetric dissociation, called Hirth lock, has the lowest energy. The reasons for the dissociation are the strong energy reduction due to the core splitting and the relaxation of elastic strains within the dissociation area. The dissociation of a⟨100⟩ edge superdislocations is the reason for their alignment in ⟨011⟩ orientation in the γ′-rafts of superalloys. However, the dissociation does not block the movement of the dislocation because they penetrate the γ′-rafts by climbing. Under loading conditions, typical for creep tests of nickel-base superalloys at high temperatures (≥1000°C), the Hirth lock slightly expands but remains stable. The asymmetric configuration is less stable and can transform into the lower energy Hirth lock.