WEB Rafting in nickel base superalloys: a phase field studyFriday (25.09.2020) 11:50 - 12:05 M: Modelling and Simulation 1 Part of:
Mechanical properties of metallic materials strongly depend on their microstructure, i.e. on the shape and spatial arrangement of the different phases in the materials. It is thus important, from both fundamental and industrial viewpoints, to understand and control the microstructure evolution. The phase field method as emerged as the most powerful method for tackling microstructure evolutions during phase transformations, especially when elastic coherency stresses are generated in solids. However, in many materials, the microstructure evolutions are coupled with a plastic activity, and there is currently a great research effort to extend the phase field method to take this coupling into account.
Within the phase field approach, plasticity can be incorporated either at the scale of dislocations or in a continuous framework. In this work, a classical phase field model is coupled to a crystal plasticity model based on dislocation densities . This model includes the anisotropy as well as the size-dependence of the plastic activity, which is expected when plasticity is confined in region below few microns in size. The model uses a storage-recovery law for the dislocation density of each glide system and a hardening matrix to account for the short-range interactions between dislocations.
The proposed coupled model will be applied in two and three dimensions to study the rafting of ordered precipitates in Ni-base superalloys. Several creep conditions will be analyzed such as tensile loadings along ,  and  directions, and the role of small misorientations around these axis will be considered.
First, the plastic driving force for rafting will be analyzed using the phase field model in which plasticity is turned off. The importance of the inhomogeneity of the shear moduli C44 and C’ will be demonstrated and rationalized using a mean field approach. Then, the plastic driving force will be considered using the full phase field model, and the evolution of the dislocation densities in the gamma channels will be analyzed. Finally, model simulations will be designed to quantitatively compare plastic and elastic driving forces.
 M. Cottura, B. Appolaire, A. Finel, Y. Le Bouar, J. Mech. Phys. Solids, 94, 473-489, 2016.