Missions

Ti-based alloys have mechanical properties superior to those of most steel grades for a density twice as low. These alloys are therefore very attractive in order to lighten structures, particularly for aeronautical applications, and thus reduce the associated carbon footprint. Among these Ti alloys, TA3V is known for its high mechanical strength while remaining easy to shape at room temperature. TA3V has a two-phase α (HCP) majority + β (CC) structure. Despite its advantages, the shaping of these alloys is not fully mastered with a very anisotropic behavior and a strong springback. Based on this observation, the ANR AFoTi project (2021 - 2024) aims to improve the understanding and prediction of the microstructural evolution and behavior of TiA3V alloys at room temperature. This project is supported by a consortium composed of LPSM (UPR3407, Villetaneuse), LEM3 (UMR7239, Metz), LGF (UMR5307, Saint - Etienne). One of the key steps of the project is to develop a physics-based macroscopic behavior law taking into account the specificities of these alloys in a multi-scale approach. The LSPM (UPR3407, Villetaneuse) proposes a postdoctoral contract whose objective will be to design and carry out DDD simulations at the mesoscale of a representative alpha grain or alpha+beta aggregate.

Activités

The proposed work will be organized as follows:
- At low temperature as well as at room temperature, the lattice friction of the HCP structure impacts the mobility of dislocations, in particular that of screw dislocations (Peierls effect). Moreover, the impurities present in TA3V (such as Al, V, O) also affect the critical cission of the different slip systems. A relevant mobility law for dislocations taking into account these effects will be defined from experimental and atomistic data in the literature.
- The interactions between the different possible slip systems in the HCP structure will be studied by DDD. The simulations will take into account the previously established dislocation mobilities as well as the elastic anisotropy.
- Massive DDD simulations will be conducted to reproduce the plastic flow and dislocation density evolution law for the HCP single crystal structure. Simulations will also be performed on bicrystals reproducing the particular geometry and orientation of α/β interfaces observed in TA3V to study their impact on the polycrystalline behavior.
- From these DDD results, constitutive behavior laws will be formulated based on recent successes for CC and CF structure materials, with which the α phase has similarities. The laws will be implemented in the Castem finite element code in combination with the MFront behavior law generator. They will be validated by confrontation with mesoscopic simulations, then confronted with experimental results

Compétences

With a Ph.D. in Materials Science or Mechanics, the candidate should have a solid experience in either atomistic (MD, DFT) or mesoscopic (DDD, would be a plus) simulations, and a thorough knowledge of crystal defects. A proven taste for simulations, scientific programming (C, python), and applied mathematics, a good level of English and an ability to work in a team are also essential.

Contexte de travail

This simulation work will be carried out at the LSPM, but a close collaboration with the LEM3 (Metz) and the LGF (Saint Etienne) will be established from the beginning of the project, to collect the necessary experimental data, and to validate our numerical approach by comparison with others developed at the LGF. National and international collaborations are also envisaged with our current partners on DDD (LEM, joint unit CNRS - ONERA) and National Laboratory Lawrence Livermore (Livermore, California, USA).

Informations complémentaires

The candidate will have to provide, on the CNRS employment portal, a detailed CV, a cover letter as well as the thesis reports; letters of recommendation can also be added to the file
.