# Berlin 2008 – wissenschaftliches Programm

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# MM: Fachverband Metall- und Materialphysik

## MM 49: Phase Transitions VI

### MM 49.4: Vortrag

### Freitag, 29. Februar 2008, 12:30–12:45, H 0107

**Phase-field simulations of cubic-cubic phase transformations under external load (application to nickel-based superalloys)** — •guillaume boussinot^{1,2}, alphonse finel^{1}, and yann le bouar^{1} — ^{1}Laboratoire d'Etude des Microstructures, ONERA/CNRS, 92320 Chatillon, France — ^{2}Institut fur Festkörperforschung, Theorie 3, Forschungszentrum, 52425 Jülich, Germany

In the case of solid-solid transformations involving cubic phases with negative anisotropy (2 C44 > C11 - C12), the three (100)-type directions are equivalent and are the directions perpendicular to which plate-like precipitates minimize the elastic energy (soft directions-Khachaturyan 1983).

When an external uniaxial stress or strain is applied, the equivalence of the (100)-type directions is broken. In superalloys, where an intermetallic phase is dispersed in a disordered matrix, this symmetry breaking leads to an anisotropic coarsening of the microstructure known as rafting. This phenomenon is of great importance in understanding the macroscopic mechanical properties of these systems (via dislocation motion which is almost restricted to the disordered phase).

We will present phase-field simulations of elastically-driven rafting (rafting can be also plastically-driven), requiring the elastic inhomogeneity between the two phases to be taken into account. Different types of rafting are then obtained, which are understood by analyzing the soft directions within an approximation of small inhomogeneity (good for superalloys).