Modelling of recovery controlled creep in nickel-base superalloy single crystals

Abstract

A model of the kinetics of recovery controlled creep in 〈001〉 oriented nickel-base superalloy single crystals has been developed. Two basic deformation mechanisms have been considered, namely (i) deformation of γ channels by slip in discrete slip systems connected with the generation of dislocations and their deposition at the γ γ′ interfaces; and (ii) dynamic recovery of the dislocation structure due to non-conservative motion (a combination of slip and climb) of dislocations along the γ γ′ interfaces and their annihilation. The climb of dislocations is conditioned by the diffusive transport of vacancies generated and annihilated at the climbing dislocations. In the steady-state creep the rate of the slip deformation in all the γ channels is in equilibrium with the recovery induced diffusional deformation. The model predicts realistic values of the steady-state creep rates and their dependence on the applied stress, as well as the strains corresponding to the end of the primary creep stage, dislocation densities at the γ γ′ interfaces and resolved shear stresses both in the γ channels and in the γ′ particles.