Experimentally-informed versus idealized simulations of dislocation-precipitate interactions
The interactions between dislocations and precipitates is one of the fundamental strengthening mechanisms for alloys. The prime examples are γ'-strengthened Ni-base superalloys. Here, the intermetallic γ' precipitate phase (Ni3Al; L12 crystal structure) is coherently embedded in the γ matrix (Ni solid solution; face center cubic (fcc) structure). Given their importance for high-temperature applications, the mechanical properties of these alloys have been thoroughly studied experimentally. However, relatively few simulations have targeted the atomic-scale interaction processes between super dislocations and γ' precipitates in polycrystalline Ni-base superalloys. Atomistic simulations of precipitate strengthening are typically conducted on regular arrays of perfectly spherical precipitates of uniform size. The so-determined precipitate strength can then be used in mesoscale modelling, e.g. by dislocation dynamics simulations. This approach is however only warranted when the fundamental mechanisms of dislocation-precipitate interactions are not affected by the size distribution or arrangement of the precipitates.
Here we show by using γ/γ'microstructures obtained from atom probe tomography (APT) in molecular dynamics (MD) simulations, that the interaction of super dislocations with a regular array of spherical precipitates with average diameter and spacing corresponding to the APT sample is qualitatively different from the experimentally-informed simulation. In particular, both, strong and weak dislocation pair coupling can be observed in the same simulation when using realistic microstructures. Furthermore, the arrangement of precipitates that are not intersected by the glide plane of the super dislocation can influence the dislocation processes through their misfit stress field. The results are discussed with respect to the importance of accounting for synergistic effects between hardening mechanisms in models for strengthening.