Development of an innovative and global numerical framework for the modeling of microstructure evolutions during metal forming industrial processes. – DIGIMU

Mechanical and functional properties of metallic materials are strongly related to their microstructures, which are themselves inherited from thermal and mechanical processing. Microstructural evolutions during thermomechanical treatments (TMT) or thermal treatments (TT) are thus of prime importance for the control of the final in-use material properties (mechanical strength, fatigue limit, crack resistance, stress corrosion resistance,...). Being able to accurately predict the microstructure obtained after complex processing routes recently became crucial for the metallurgy industry, and is a real challenge from a scientific point of view. Completing this challenge requires the development of numerical modeling capabilities based on realistic description of the intricate multiscale physical phenomena undergone by the material under processing.

A precise numerical modeling of materials is then a topic of prime importance largely due i) to the demonstrated value of predictive simulations of materials behavior in greatly reducing the time and cost of developing new materials or new processing routes and ii) to the theoretical interest of such strategies to improve our understanding of metallurgical phenomena. Morevover, from improvement of the nickel-based superalloys used in critical parts of aircraft engines in order to increase their efficiency to the stainless steels used in nuclear power plants which place unusual demands on the metallic materials through the lightening of structures in automotive and aeronautics industries, the needs are tremendous. Thus, microstructure predictions during TMT is a cornerstone of all the industrial partners of the DIGIMU chair, i.e. ArcelorMittal INDUSTEEL, AREVA, AUBERT & DUVAL, ASCOMETAL, CEA, SAFRAN and TRANSVALOR.

Despite the obvious industrial interest for modeling accurately microstructure evolution during metallic materials forming, there are only very few studies addressing this problem in an industrial context. In order to predict precise evolution of grain size distribution and morphologies as well as the evolution of different phase fractions and topologies, a global numerical strategy remains to be invented and built. We contend that developping this realm requires, firstly, the development of a unified groundbreaking finite element (FE) full field numerical strategy and, secondly, the development of a powerful multiscale strategy in order to develop more and more accurate mean field models.

Through the DIGIMU chair, the candidate for the chair and the other researchers involved will organize a unified modeling effort dedicated to multiscale simulation of microstructure evolution thanks to a new very promising full field FE approach and will industrialize the outcome of that work in the form of a FE software package called DIGIMU.

Modeling of recrystallization (ReX) and grain growth (GG), prediction of abnormal grain growth (AGG) and modeling of solid-solid phase transformations (SSPT) are mainly aimed. Moreover, a large piece of the proposed work will also be dedicated to experimental investigations and validations. Two main classes of metallic materials will be considered: austenitic stainless steels (304L and 316L) and nickel-based superalloys (Inconel 718, AD730 and N19). It is worth mentioning that the described physical phenomena do have a generic character, so that it will be possible afterwards to use the numerical developments for other types of metallic materials.

The main numerical developments will concern the ability, in a FE context, to describe real or representative microstructures and to model grain and/or phase boundary motions. Moreover, a multiscale (full field/main field) approach will be developed in order to automatically improve the developed mean field models thanks to the results of the full field simulations.