Influence of dislocation climb on the creep rates in γ'-strengthened Ni base superalloy single crystals: A discrete dislocation dynamics study

S.M. Hafez Haghighat¹, Eggeler G², D. Raabe¹ ¹ Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237 Düsseldorf, Germany ² Institut für Werkstoffe, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany

Creep of single crystal superalloys is governed by dislocation glide, climb, reactions, and annihilation. We use discrete 3D dislocation dynamics (DDD) simulations to study the evolution of the dislocation substructure in a γ/γ’ microstructure of a single crystal superalloy for different climb rates and loading conditions.

Fig. 1. Trajectory of the movement of a typical mixed ½a0{111} dislocation from position A to position B by either glide-climb or climb motion along the γ/γ´ interface. Finally, the dislocation is released from the corner of the γ´ particle, where it then penetrates into the γ channel parallel to the applied stress direction.

© Max-Planck-Institut für Eisenforschung GmbH

Fig. 1. Trajectory of the movement of a typical mixed ½a0{111} dislocation from position A to position B by either glide-climb or climb motion along the γ/γ´ interface. Finally, the dislocation is released from the corner of the γ´ particle, where it then penetrates into the γ channel parallel to the applied stress direction.

© Max-Planck-Institut für Eisenforschung GmbH

A hybrid mobility law for glide and climb is used to map the interactions of dislocations with γ’ cubes. We focus on the early stages of creep, where dislocation plasticity is confined to narrow γ channels. With enhancing climb mobility the creep strain increases even if the applied resolved shear stress is below the critical stress that is required for squeezing dislocations into the γ channels. The simulated creep microstructure consists of long dislocations and a network near the corners of the γ’ precipitate in the low stress regime. In the high stress regime, dislocations squeeze into the γ channels where they deposit dislocation segments at the γ/γ’ interfaces. These observations are in a good agreement with experimentally observed dislocation structures which form during high temperature and low stress creep.