Physical interpretation of creep in single crystal René N4TM based on a phenomenological model

Abstract

Creep and rafting in Ni-based single crystal René N4 is described using reported phenomenological models after modifying the creep model to represent the rafting induced hardening of the structure against creep and the greater propensity for shearing of γ′ as the structure rafts and dislocation density in the channels and γ/γ′ interface builds up. The proposed model can describe the creep strain evolution at 1144K over the stress range 241–413MPa. The rafting model is shown to provide an adequate representation of horizontal and vertical channel width evolution at 1144K and 1255K. The variation of the physical parameters in the creep model viz., back stress, dislocation density and shear rate is rationalized scientifically thereby substantiating the physical basis of the model. The development of back stress in the channels is explained mechanistically through the deposition of dislocation segments at γ/γ′ interface by the Orowan loops expanding in the channel and the recovery of the interfacial dislocation networks. The evolution in Orowan stress consequent to rafting and its effect on dislocation activity are elucidated. The evolution of the kinetics for dynamic and static recovery processes which accompany creep strain accumulation has also been explained mechanistically.