Effect of climb on dislocation mechanisms and creep rates in gamma’-strengthened Ni base superalloy single crystals: A discrete dislocation dynamics study
Creep of single-crystal superalloys is governed by dislocation glide, climb, reactions and annihilation. Discrete three-dimensional (3D) dislocation dynamics (DDD) simulations are used to study the evolution of the dislocation substructure in a gamma/ gamma’ microstructure of a single-crystal superalloy for different climb rates and loading conditions.
![Predicted creep microstructure of a single-crystal Ni base superalloy deformed to a creep strain of 0.5% at 150 MPa along the x=[100] direction viewed from the y and z directions. Similar microstructures observed by multibeam DF-STEM diffraction contrast characterization.](/3752068/original-1551349635.jpg?t=eyJ3aWR0aCI6MzQxLCJmaWxlX2V4dGVuc2lvbiI6ImpwZyIsIm9ial9pZCI6Mzc1MjA2OH0%3D--ac1fee013319d45c452e628b1cdd4fd9b0bb90a5 "Predicted creep microstructure of a single-crystal Ni base superalloy deformed to a creep strain of 0.5% at 150 MPa along the x=[100] direction viewed from the y and z directions. Similar microstructures observed by multibeam DF-STEM diffraction contrast characterization.")
![Predicted creep microstructure of a single-crystal Ni base superalloy deformed to a creep strain of 0.5% at 150 MPa along the x=[100] direction viewed from the y and z directions. Similar microstructures observed by multibeam DF-STEM diffraction contrast characterization.](/3752068/original-1551349635.jpg?t=eyJ3aWR0aCI6MjQ2LCJvYmpfaWQiOjM3NTIwNjh9--be0ed0073a705ec625bdb45758a85310a5eafc8c)
Predicted creep microstructure of a single-crystal Ni base superalloy deformed to a creep strain of 0.5% at 150 MPa along the x=[100] direction viewed from the y and z directions. Similar microstructures observed by multibeam DF-STEM diffraction contrast characterization.
A hybrid mobility law for glide and climb is used to map the interactions of dislocations with c0 cubes. The focus is on the early stages of creep, where dislocation plasticity is confined to narrow gamma channels. With enhancing climb mobility, the creep strain increases, even if the applied resolved shear stress is below the critical stress required for squeezing dislocations into the c channels. The simulated creep microstructure consists of long dislocations and a network near the corners of the gamma’ precipitate in the low-stress regime. In the high-stress regime, dislocations squeeze into the gamma channels, where they deposit dislocation segments at the gamma/ gamma’ interfaces. These observations are in good agreement with experimentally observed dislocation structures that form during high-temperature and low-stress creep.