Towards a precise description of the mobility and its numerical integration in finite element modeling of recrystallization mechanisms
In order to accurately describe the 3D evolution of polycrystals (recrystallization, phase transformations…), full-field methods such as the phase-field (PF) or the level-set (LS) methods currently represent the best option. In this context, a new FE numerical framework to model grain growth (GG) and recrystallization (ReX) based on a LS description of the interfaces and meshing/remeshing capabilities has been recently developed in a static context  or a dynamic one . LS method is also particularly interesting for the modeling of Smith-Zener pinning. These PhD works will be dedicated to the enhancement of the existing numerical formalism in order to be able, in a smart and efficient way, to deal with strong and local anisotropies of mobility. This aspect is today a big numerical challenge for existing full field numerical approaches but also an open question from a metallurgical point of view. These developments will be motivated, criticized and validated thanks to experimental investigations on 304L and 316L stainless steels. Finally, the resulting developments will be impleted in the DIGIMU software packing.
 B. Scholtes, R. Boulais-Sinou, A. Settefrati, D. Pino Muñoz, I. Poitrault, A. Montouchet, N. Bozzolo, and M. Bernacki. 3D level set modeling of static recrystallization considering stored energy fields. Computational Materials Science, 122:57-71, 2016.
 L. Maire, B. Scholtes, C. Moussa, N. Bozzolo, D. Pino Muñoz, A. Settefrati, and M. Bernacki. Modeling of dynamic and post-dynamic recrystallization by coupling a full field approach to phenomenological laws. Materials & Design, 133:498-519, 2017.
Influence of grain boundary pinning on recrystallized grain size homogeneity : multiscale modelling and application to nickel based superalloys used in aeronautic industry
During the last six decades, Smith-Zener pinning phenomenon has been widely studied and many different analytical models have been proposed in the literature. In this context, abnormal grain growth (AGG) is a versatile phenomenon and its prediction is extremely complex. AGG can be seen as a particular metallurgical configuration where few grains grow much faster than the mean grain growth rate, leading to a bimodal grain size distribution or eventually to a single population of very large grains. At stable subsolvus configuration, if only capillarity force is considered, this phenomenon is always driven by a kind of growing advantage for some grains comparatively to their neighbours (grain size, high anisotropy of boundary energy and/or boundary mobility) but this phenomenon can also be triggered by critical stored energy distributions. In the last case, even if AGG remains the accepted term in the literature, we should rather discuss of a particular regime of ReX. Recently, a new level-set (LS) numerical approach to consider inert second phase particles (SPP) in a FE framework has been proposed and used to perform 2D GG and static recrystallization (SRX) simulations for Inconel™ 718. Such approach seems very promising in context of AGG. Indeed, the Smith-Zener drag effect is naturally modeled by the modification of the local mean curvature when the grain boundaries pass through the particles. AGG in 2D framework, critical stored energy context and stable subsolvus configuration were also discussed thanks to this method . Next steps that we will consider in the proposed work will be to deal with realistic and large 3D simulations by considering all the different metallurgical mechanims which can lead to overgrown grains. Possible evolutions of second phase particles and resulting interactions with grain interfaces in context of near-solvus static TT will be studied. Homogenization will also be considered in order to build improved mean field models. Moreover a large piece of the proposed work will also be dedicated to experimental investigations. Firstly, large databases capitalized by the DIGIMU industrial partners concerning microstructure evolutions of Inconel™ 718 during TMT will be used to discuss the full field simulations and the proposed new main field models. Secondly, in order to validate more finely the different modeled mechanims for more prospective materials, TMT and microstructural characterizations will be realized for two other nickel-based superalloys: N19™ and AD730™.
 A. Agnoli, M. Bernacki, R. Loge, J.-M. Franchet, J. Laigo, and N. Bozzolo. Selective growth of low stored energy grains during sub-solvus annealing in the inconel 718 nickel base superalloy. Metallurgical and Materials Transactions A, 46(9):4405-4421, 2015.