Idealized vs. Realistic Microstructures: An Atomistic Simulation Case Study on γ/ γ ^′ Microstructures

Abstract

Single-crystal Ni-base superalloys, consisting of a two-phase γ/ ${\gamma }^{\prime }$ microstructure, retain high strengths at elevated temperatures and are key materials for high temperature applications, like, e.g., turbine blades of aircraft engines. The lattice misfit between the γ and ${\gamma }^{\prime }$ phases results in internal stresses, which significantly influence the deformation and creep behavior of the material. Large-scale atomistic simulations that are often used to enhance our understanding of the deformation mechanisms in such materials must accurately account for such misfit stresses. In this work, we compare the internal stresses in both idealized and experimentally-informed, i.e., more realistic, γ/ ${\gamma }^{\prime }$ microstructures. The idealized samples are generated by assuming, as is frequently done, a periodic arrangement of cube-shaped ${\gamma }^{\prime }$ particles with planar γ/ ${\gamma }^{\prime }$ interfaces. The experimentally-informed samples are generated from two different sources to produce three different samples—the scanning electron microscopy micrograph-informed quasi-2D atomistic sample and atom probe tomography-informed stoichiometric and non-stoichiometric atomistic samples. Additionally, we compare the stress state of an idealized embedded cube microstructure with finite element simulations incorporating 3D periodic boundary conditions. Subsequently, we study the influence of the resulting stress state on the evolution of dislocation loops in the different samples. The results show that the stresses in the atomistic and finite element simulations are almost identical. Furthermore, quasi-2D boundary conditions lead to a significantly different stress state and, consequently, different evolution of the dislocation loop, when compared to samples with fully 3D boundary conditions.