Tailored Large-Scale Atomistic Simulations of Regular and Inverted Microstructure Ni-base Superalloys

Ni-base superalloys are a class of chemically complex alloys which have excellent thermomechanical properties. Their microstructure presents or- dered L12 Ni3Al cuboidal γ′-precipitates embedded in a disordered FCC Ni γ- matrix. These precipitates act as barriers to the motion of extended crystalline lineal defects called dislocations, which is at the root of irreversible plastic de- formation. The relative stability of these precipitates under different loads and temperature regimes which can reach ˜90% of the melting point of its major con- stituent, Ni, make these alloys ideally suited to being used in the turbine blade and disk components commonly applied in the aerospace and power generation industries. In addition, depending on alloy composition and alloy heat treatment history, the γ-phase can again form within the γ′-precipitates, causing an addi- tional barrier to dislocation motion and leading to additional strengthening. The mechanisms through which dislocation motion is impeded all have their origin at the atomic scale. In this thesis, we present semi-empirical atomic scale simulations using molecular statics and molecular dynamics on tailored model atomic config- urations, performed to study the interplay between material properties, interphase boundary characteristics, dislocation character, local chemical environment, and dislocation evolution within either phase and from one phase to the next. Molecu- lar dynamics simulations of the Re-effect and of compression tests of free-standing γ′-nanocubes are also presented, and discussed in the context of dislocation evolu- tion within the γ/γ′-microstructure and at the interphase boundaries. The use of so-called tailored toy models and of a simplistic chemistry to discuss the material behavior of complex multinary alloys is rationalized.