Subject: Martensite is a microstructural constituent that provides high strength to various classes of steels. Martensite is sensitive to low-temperature ageing. In the first stage of ageing, carbon atoms segregate to the structural defects (dislocations, twin and grain boundaries). They also form nanosized clusters in the bulk. It is often assumed that carbon clustering occurs by spinodal unmixing of the supersaturated solid solution since the resulting nanostructure consists of iron carbides alternating with carbon-depleted zones. This nanostructure produces an increase in the metal hardness.
Characterization and simulation of the kinetics of carbon segregation and clustering must be performed at the atomic scale. In this purpose, a kinetic Monte Carlo model has been developed in our research group. Based on fundamental parameters computed ab initio and on the interaction of carbon atoms with the homogenous elastic strain, simulations were able to predict original phenomena such as high diffusion anisotropy , non-linear elastic behavior  and giant Snoek relaxation . Segregation and clustering are spatially heterogenous: they require to account for the short-range “chemical” and the long-range elastic carbon-carbon interactions. These interactions modify both the atomic mobility and the driving force for nanostructure evolution.
The work of the post-doctoral fellow will consist in introducing in the Monte Carlo program the carbon-carbon interactions in the framework of the elasticity theory of point defects, via the formalism of the force-dipole tensors. The expected outputs are the influence of carbon content, temperature and external stress on carbon diffusivity, spatial distribution in Cottrell atmospheres and the kinetics of spinodal decomposition.
Working laboratory: IM2NP, Aix-Marseille University, CNRS. The host group is Reactivity of Interfaces, whose research topics cover the atomic-scale characterization and modelling of interfacial segregation and reactivity in semi-conductors and steels.
Funding. The project is funded by a German-French ANR program bringing together four laboratories. Salary will be in the range of 2200 to 3100 €/month after taxes, depending on the applicant’s experience. The funding includes a support for attending conferences and missions.
Contact. Send a CV and cover letter to P. Maugis (firstname.lastname@example.org), plus references (email of previous supervisors).
 P. Maugis, S. Chentouf, D. Connétable, J. Alloys Compd. 769 (2018) 1121–1131.
 P. Maugis, Comput. Mater. Sci. 159 (2019) 460–469.
 P. Maugis, Materialia 12 (2020) 100805.Continue reading
|Title||Postdoc position – Atomic-scale simulation of carbon segregation and clustering in Iron-Carbon martensite|
|Employer||Institut Matériaux Microélectronique Nanosciences de Provence (IM2NP)|
|Job location||Faculté des Sciences de Saint Jérôme - Case 142, Avenue Escadrille Normandie Niemen, F-13397 Marseille Cedex 20, 13397 Marseille|
|Published||December 7, 2020|
|Job types||Postdoc  |
|Fields||Nanotechnology,   Materials Chemistry,   Solid-state Chemistry,   Atomic, Molecular and Optical Physics,   Materials Physics,   Solid-state Physics  |