On the cross-slip of screw dislocations in zirconium

Abstract

We develop here a cross-slip model for zirconium based on discrete dislocation dynamics and explicit representation of partial dislocations. It is found that the basal-to-prismatic cross-slip is always energetically favorable. The corresponding stress-free activation enthalpy is ΔHa*∼0.5eV, and the critical nucleation length is close to zero. The Escaig stress on the primary plane is found to be the most effective component in influencing the activation enthalpy. By contrast, prismatic-to-basal cross-slip is activated only if the Schmid stress on the conjugate plane is higher than ∼1GPa, with an activation enthalpy larger than 5 eV. We propose that basal slip of 〈a〉 screw dislocations in Zr is mediated by the formation and subsequent lateral migration of kink pairs formed by double cross-slip. The proposed mechanism is consistent with experimental observations on the temperature-dependence of the critical resolved shear stress (CRSS) and the wavy motion of 〈a〉-basal slip.