June 15, 2017
PhD position in two research laboratories: LEM3 at Metz and PPRIME Institute at Poitiers
in the framework of Labex DAMAS (Lorraine University)
“Understanding the mechanisms of micro-propagation of cracks in steels with microstructure gradients obtained by Ultrasonic Shot Peening”
The proposed study concerns both microstructural approaches and mechanical aspects of the problem; therefore, in order to have an optimal working environment, the thesis will be carried out in two research laboratories: LEM3 at Metz and PPRIME Institute at Poitiers.
Thesis co-supervisor(s) and supervising team:
Dr. Mandana ARZAGHI (P’), Dr. Roxane MASSION (LEM3), Pr. Yves NADOT (P’), Pr. Thierry GROSDIDIER (LEM3)
The improvement in the properties of components is often strongly related to the performance Of thuiň surfaces which can be subjected to severe thermo-mechanical loadings. Functionally Graded Material (FGM) belongs to a class of advanced materials with varying properties over a changing dimension. Surface treatments such as Surface Mechanical Attrition Treatment (SMAT) or Ultrasonic Shot Peening (USP), significantly improve the mechanical properties at the surface and over several hundreds of microns within the sub-surface. This is due to the severe plastic deformation and associated formation of a refined microstructure where the presence of grain and twin boundaries (nanoscale) contributes to a significant increase in mechanical strength.
In the domain of fatigue, rotative bending tests on steels having a surface microstructure gradients have confirmed the potential for improving properties under cyclic loads. Post-rupture analyzes also highlighted the importance of surface finish on crack initiation and propagation.
The objective of the present thesis is to better understand the mechanisms of micro-propagation of cracks in microstructure gradient steels having different characteristics regarding the grain / phase boundaries. To this end, three steels with different stacking fault energies will be processed by USP and characterized for their structure evolution: size of the microstructural elements, the amplitude of the micro-stress gradients and the nature of the grain boundaries by MET, DRX and EBSD. Uniaxial fatigue tests in air, at ambient temperature and force controlled will be carried out on macroscopic specimens, with or without USP treatment, in order to plot and interpret the SN curves (particular attention will be paid to the initiation and micro crack propagation mechanisms). These macroscopic investigations will be followed by in-situ fatigue tests in a SEM (new facility under development) in order to determine the mechanisms that govern the micro-propagation of cracks.
Funding and starting date:
The project is supported and financed by LabEx DAMAS and PPRIME Institute. In accordance with the relevant standards applied at the university defined in the â€śfixed-terms contractâ€ť, a net monthly salary of about 1600 euros including social security and retirement contribution will be provided for a period of 36 months. Desired starting date: October 2017.
Post-Doctoral Researcher at LEM3 (CNRS UMR 7239) – Metz – France
in the framework of Labex DAMAS (Lorraine University)
Development of the TKD method in a new configuration for orientation mapping at a nanometer scale.
Keywords: Transmission Kikuchi Diffraction in SEM (TKD), Electron Microscopy, Orientation Imaging Microscopy, Nanomaterials.
You will join the 3TAM group in the LEM3 and work on a research topic selected by the Laboratory of Excellence DAMAS. The 3TAM group is involved in the development of innovative methods for characterizing microstructure and crystallographic texture of materials and is expert to relate their evolution during thermo-mechanical treatments to the mechanical properties.
The TKD technique has been recently introduced as a SEM based method capable of giving orientation maps as the EBSD method but with a spatial resolution improved by up to one order of magnitude . The technique requires a specimen thin enough to be transparent to the electron beam. In the current configuration, it uses hardware and software developed for the EBSD technique.
We proposed a new configuration of the TKD where the detector is disposed horizontally on the axis of the microscope instead of being vertically positioned as in the conventional configuration. This achieves better spatial resolution and angular resolution than the ones of the current TKD configuration [2, 3, 4]. Moreover, acquisition times are shorter than in the conventional technique, because the intensity of the forward scattered electrons is much higher than that of the large angle scattered electrons.
The work will consist in two main tasks.
- The first concerns the spatial resolution of the TKD method: the lateral spatial resolution and the depth spatial resolution. In order to estimate these ones, it is essential to know where the detectable diffraction mainly occurs within the specimen thickness. First experiments on bilayer specimens have shown that it is mainly the bottom part of the specimen which contributes to the detected diffraction pattern. To analyze that more quantitatively, you will have to do Monte Carlo simulations of the electron trajectories through the specimen. It should allow to estimate what is the effect of the specimen thickness on the spatial resolution? Is there an influence to use our configuration or the conventional one? Could a change of voltage modify it?
- The second concerns the applications. As this method is new, the field of possible applications is not yet well defined. You will have to explore it. Due to its spatial resolution of few nanometers, it is well suited to study nano-structured materials. For example, ultrafine structure of metallic alloys obtained by Strong Plastic Deformation (SPD) can be characterized in order to better understand the mechanisms of grain subdivision during SPD. Another type of application concerns the electron damage sensitive materials because low voltage and low electron probe current can be used.
 R.R. Keller, R.H. Geiss, J. Microsc.245 (2012) 245-251.
 J.J. Fundenberger, E. Bouzy, D. Goran, J. Guyon, A. Morawiec, H. Yuan, Microsc. Microanal. 21 (S3) (2015) 1101-1102.
 J.J. Fundenberger, E. Bouzy, D. Goran, J. Guyon, H. Yuan, A. Morawiec, Ultramicroscopy 161 (2016) 17-22.
Requirements: Ph.D. in Materials Science or in Physics. Experimental skills and theoretical knowledge in material characterization by electron microscopy, particularly in SEM + EBSD and TEM. Experience in preparation of TEM specimens by FIB and Monte-Carlo simulations would be appreciated. A good level of written English is essential.
Deadline: June 30 2016. The following documents must be sent by e-mail to Prof. Emmanuel Bouzy : cover letter describing your research interest and why you are suitable for this position (maximum 1 page) – CV and list of publications – Names, e-mail addresses, and telephone numbers for two academic references.
Expected start dateÂ and duration: as soon as possible from March 2016 for one year. (possible extension for one year)
Net salary: 2200 Euros.
Further information : E. Bouzy firstname.lastname@example.org Tel : +33 (0)3 87 31 53 96
J.-J. Fundenberger email@example.com Tel : +33 (0)3 87 31 53 27
LEM3 UMR CNRS7239 â€“ UniversitĂ© de Lorraine – Ile du Saulcy â€“ 57012 METZ Cedex 01 â€“ France.
October 22, 2015
PhD position at IJL (CNRS UMR 7198) â€“ Nancy â€“ France
in the framework of Labex DAMAS (Lorraine University)
” Recovery of inclusion aggregates in metallurgical processes, role of the local turbulence at the free surface and at the walls “
Place of work: Institut Jean Lamour, Labex DAMAS, Nancy, France
Advisors: Dr. Jean-SĂ©bastien Kroll-Rabotin and Prof.Jean-Pierre Bellot
Scientific context and work environment:
Mass lowering of metallic structures has become a key challenge in the industries related to aerospace, energy and high technology that require high performance materials and well controlled quality of the materials. The Excellent Laboratory Labex DAMAS addresses this important issue and the enclosed project is involved in the Labex.
The inclusion populations (micronic particles with a different chemical nature of those of the metal) strongly impact the mechanical performances of the alloys, in particular fatigue resistance. These particles are conditioned during the very early stages of the metallurgical process, before solidification. Controlling the mechanical performances thus requires controlling the inclusion populations, which in turn requires a deep knowledge of the inclusion recovery mechanisms at play during the elaboration of alloys, in liquid phase. For example, the critical size of the tolerated inclusions in aluminum alloys, steels and superalloys has constantly been decreasing to address the evolution of industrial needs.
The behavior of inclusions in metallurgical processes has already been studied with a good level of details by people involved in this project, essentially via numerical simulations [1, 2]. At such a scale, inclusion transport and agglomeration phenomena have to be modeled, which circumscribes the conclusions drawn from such simulations to the domain of accuracy of the underlying models. This project aims at specifically studying the deposition and capture of metallurgical inclusion aggregates on walls and free surfaces using mesoscopic simulations (few hundreds of micrometers), in which particles and flow at particle scale are fully resolved. Such simulations will provide a better understanding and identification of the significant deposition and capture mechanisms, including the morphology and the physico-chemical properties of the inclusions. In a second time, mesoscopic simulations will be used to build up kinetic laws of deposition that can be used in larger scale simulations, as a way to improve the control of inclusion recovery, and as a consequence inclusion cleanliness, in industrial processes.
For this work, the simulations will be performed using computation software that is being developed in the hosting team and that already serves to simulate primary inclusion interaction and aggregation in a liquid metal. It is based on a lattice Boltzmann method (LBM)  to solve the flow dynamics (CFD) and on a discrete element method (DEM)  to track solid inclusions. The coupling between the two methods uses immersed boundaries (IBM)  in order to fully resolve the geometry of the considered inclusions.
Applicants to this PhD position must have an education of good quality in fluid mechanics and must be interested in numerical simulations. General knowledge of numerical methods and common simulation techniques will be very appreciated but no former experience with lattice Boltzmann or discrete element methods is required.
This work to be done falls in a long term research theme of the Process Metallurgy team that the applicant would join. However, mesoscopic simulations at inclusion scale is a recent development. Applicants must thus prove curious, eager to learn new simulation tools, and able to draw physical interpretations from simulation results based on their knowledge in fluid mechanics. They must also be comfortable with mathematical modeling since models will have to be written in statistically consistent form to be suitable for integration in a population balance equation.
 J.-P. Bellot, V. Descotes, and A. Jardy, â€śNumerical modelling of inclusion behaviour in liquid metal processingâ€ť, JOM, vol. 65, no. 9, pp. 1164â€“1172, 2013.
 J.-P. Bellot, V. De Felice, B. Dussoubs, A. Jardy, and S. Hans, â€śCoupling of CFD and PBE calculations to simulate the behavior of an inclusion population in a gas-stirring ladleâ€ť, Metallurgical and Materials Transactions B, vol. 45, no. B, pp. 13â€“21, 2014.
 J. J. Derksen, â€śHighly resolved simulations of solids suspension in a small mixing tankâ€ť, AIChE Journal, vol. 58, p. 3266, 2012.
 J.-S. Kroll-Rabotin, R. Sungkorn, S. A. Hashemi, J. J. Derksen and R. S. Sanders, â€śLarge eddy simulation of a solid-liquid fluidized bed using the lattice-Boltzmann method and a soft-sphere collision modelâ€ť, in Ninth International Conference on CFD in the Minerals and Process Industries, CSIRO, 2012.
Contact: Jean-SĂ©bastien Kroll-Rabotin firstname.lastname@example.org