The interaction between dislocations and precipitates is one of the archetypical hardening mechanisms in alloys and plays together with solid solution strengthening a critical role for the high (creep) strength of superalloys. Precipitation hardening in superalloys has been intensively studied, e.g., through TEM observations of interrupted creep tests, and more recently by in-situ micromechanical tests. Analytical and numerical models can successfully describe many aspects of strengthening on the meso- and macroscale. However, such models as discrete dislocation dynamics (DDD) simulations require parameters, which depend on the atomic-scale details of the dislocation – precipitate interactions. Atomistic simulations can in principle provide such information but are currently severely limited by the lack of accurate atomic interaction potentials for technologically relevant, multi-component alloys and by the difficulties to include diffusive processes. Therefore, there are currently still relatively few atomistic simulations of dislocationprecipitate interactions in superalloys.

Here we present an overview of our atomistic simulations in the Ni-Al-(Re) system as model for γ/γ’ strengthened alloys. We show that while parameters like the cutting-stress for dislocations to enter γ’ precipitates can be obtained from idealized geometries, the details of the γ/γ’ interface structure, the precipitate morphology and arrangement can severely influence the dislocationprecipitate interactions. In particular the curvature of the γ/γ’ interface can affect the misfit dislocation network, as demonstrated using experimentally obtained γ/γ’ interface morphologies. The local interface orientation not only alters the misfit dislocation core structure but can also facilitate the formation of ⟨100⟩ dislocations at the interface. Furthermore, the spatial arrangement and size-distribution of spherical γ’ precipitates, e.g., in disk-alloys, can lead to synergistic effects that are not present in the typical models of precipitate strengthening based on the interaction of straight dislocations with a regular array of uniform precipitates. Certain Ni-base superalloys furthermore form γ precipitates inside the cuboidal γ’ phase. Our simulations suggest that the misfit stresses caused by the γ precipitates reduce the yield stress of γ’ cubes subjected to nanomechanical compression tests. The situation is, however, different when the deformation is not controlled by the nucleation of dislocations, e.g., when the γ’ cubes are embedded in a dislocation-containing γ matrix. In this case, the γ precipitates lead to an additional hardening that is also observed experimentally.

We close by providing an overview of recent simulation methods that allow to include diffusive processes in the study creep mechanisms at the atomic scale.