Theme: Research
PhD defence of Matheus Brozovic Gariglio
2 February 2023
Matheus Brozovic Gariglio defends his PhD in Computational Mechanics and Materials on Feb. 2, 23
A multiscale study of microstructural evolutions in hot-deformed two-phase titanium alloys
Matheus Brozovic Gariglio conducted his PhD work under the supervision of Nathalie Bozzolo (MSR team) and Daniel Pino Munoz (CSM team). He defends his PhD in "Computational Mechanics and Materials" on February 2nd, 23 in front of the following jury:
– Olivier CASTELNAU, Arts et Métiers, reviewer
– Maria Cecilia POLETTI, Graz University of Technology, reviewer
– Christian DUMONT, Aubert & Duval
– Jérôme DELFOSSE, SafranTech
– Frédéric PRIMA, Chimie Paris – PSL
– Nathalie BOZZOLO, Cemef Mines Paris – PSL
– Daniel PINO MUNOZ, Cemef Mines Paris – PSL
Abstract:
Titanium alloys are widely used in the aeronautical industry, thanks to their properties of resistance to temperature and corrosion, but above all their low density. These properties are strongly linked to the microstructure, itself resulting from the hot forging operations implemented to manufacture industrial parts. The optimization of the properties therefore requires controlling the impact of the thermomechanical parameters on the microstructure evolution. The two-phase (α/β) nature of certain titanium alloys offers, for a given grade, a very wide variety of possible microstructures, thus a certain flexibility in the adjustment of the properties. Two titanium alloys are studied in this work: the Ti-6Al-4V (α+β) alloy used in turbojet, and the Ti-10V-2Fe-3Al (metastable-β) alloy used in landing gears. The main objective of this work is to evaluate and describe how the dislocation density is distributed between the α and β phases, depending on the thermomechanical parameters and the initial microstructure. Three distinct and complementary approaches are implemented: experimental at the microscopic and at the macroscopic scale, as well as by numerical simulation. A large part of the results of this thesis come from fine microstructural analyses, mainly in the form of orientation maps obtained by electron backscattered diffraction (EBSD), but also in the form of complementary three-dimensional characterizations. Advanced EBSD data post-processing techniques are used to assess dislocation densities from measured intragranular misorientations. The macroscopic approach is based on the analysis of stress-strain curves from hot compression tests. Finally, full-field plastic deformation simulations are performed on artificial and experimental microstructures. The discussion confronts the results obtained by these three approaches and shows that any direct comparison should be avoided. For each of the phases, key microstructural elements, mainly in terms of crystallographic texture and dynamic recrystallization, are given in order to link these approaches to better estimate the dislocation density, therefore of microstructure evolution. This work provides elements for a better understanding of the behavior of titanium alloys, assisting the industrial financial partners (Airbus, Aubert & Duval, Safran and Timet) to optimize the forging routes.
Keywords: Microstructure, titanium, hot deformation, two-phase, EBSD, dislocation density
Juhi Sharma, winner of the 2nd Bodycote SF2M 2022 prize
12 January 2023
La SF2M récompense les travaux de thèse de Juhi Sharma par son prix bodycote.
The French Society of Metallurgy and Materials, SF2M, has awarded its 2nd Bodycote prize to Juhi Sharma, PhD from CEMEF.
Juhi Sharma completed her PhD thesis in the MSR team, under the supervision of Nathalie Bozzolo and Charbel Moussa. She worked on "Microstructure evolution during hot forging of VDM Alloy 780: mechanisms, kinetics and medium field modelling". Juhi Sharma defended her thesis on 22 October 2021.
The award ceremony took place during the SF2M day on 15 December 2022 in Paris on the theme of "reasoned choice of materials".
Congratulations to Juhi Sharma for this great recognition of his research work. Juhi had also obtained the 1st Pierre Laffitte Prize in 2020.
The SF2M Bodycote Prize in a few words:
This prize rewards students and young researchers for innovative and applicative research and/or development work on the improvement of:
– core and surface properties of metallic materials,
– characterisation and testing methods,
– production processes and techniques,
following thermal, thermochemical and surface treatments, or assembly methods by welding (electron beam vacuum welding only) or brazing (all technologies).
SF2M picture taken during the ceremony, on Dec. 15th, 2022.
Dr. Juhi Sharma on the right, Dr. Patrick Jacquot (Technical Director Bodycote) in the center, and Steve Gaudez (1st Bodycote prize) on the left.
PhD defence of Emile Hazemann
19 December 2022
Emile Hazemann defends his PhD in Computational Mechanics and Materials on Dec. 19, 22
Study of recrystallized grains occurence in single crystal nickel-based superalloys for turbine blades application
Emile Hazemann conducted his PhD work under the supervision of Charles-André Gandin, Michel Bellet, Yancheng Zhang (2MS team) and Karim Inal (PSF team). He defends his PhD in "Computational Mechanics and Materials" on December 19, 22 (subject to the agreement of the reviewers) in front of the following jury:
– M. Jonathan CORMIER, Institut P' CNRS-Université de Poitiers-ISAE ENSMA
– M. Carl LABERGERE, Université de Technologie de Troyes
– Mme Virginie JAQUET, Safran Aircraft Engines
– M. Roland FORTUNIER, Ecole Nationale d'Ingénieurs de Saint Etienne
– Mr Charles-André Gandin, CEMEF Mines Paris – PSL
– Mr Michel Bellet, CEMEF Mines Paris – PSL
– Mr Karim Inal, CEMEF Mines Paris – PSL
– Mr Yancheng Zhang, CEMEF Mines Paris – PSL
Abstract:
The current work’s aim is to understand recrystallized grains formation in single-crystal nickel-based superalloys for turbine blades application. The presence of such grains, with large misorientation compared to the single-crystal’s orientation, is prohibitive because it decreases dramatically the mechanical behaviour of the part. On one hand, nucleation of recrystallized grains is related to the amount of strain introduced in the alloy during solidification and cooling, and on the other hand, to subsequent heat treatment. To predict nucleation and growth of recrystallized grains, one needs to identify 1) the mechanical behaviour of the alloy during solidification and cooling 2) a recrystallization criterion based on the mechanical state of the matter. The present work is built around these two research axes, specifically for CMSX-4, a second-generation nickel-base superalloy. In the first axis, we identify as-cast CMSX-4 behaviour with an elastic viscoplastic constitutive law, using tensile-relaxation tests and finite elements modelling. The identified model considers single crystal anisotropy at temperatures and strains rates representative of casting process. The parameters of the constitutive laws are identified using inverse analysis, using tensile-relaxation tests, at constant temperatures, on as-cast CMSX-4 samples with tensile direction oriented along <001>, <110> and <111> crystallographic orientations. Tests are performed with a resistive heating machine, using contactless instrumentation (infrared pyrometry and digital image correlation). In the second axis, our interest is to reproduce thermomechanical paths of areas that are critical regarding recrystallization in a turbine blade, during solidification and cooling. These paths are simulated with tensile tests at different stress rates and a constant cooling rate, for specimens with different orientations. Tested specimens undergo standard homogenization heat treatment to reveal or not the presence of recrystallized grains. Thermo-mechanical paths are then simulated with constitutive law identified in the first axis, to identify a recrystallization criterion.
Keywords: Recrystallization, Mechanical behaviour, Nickel-based superalloys, Microstructure, CMSX-4, Modelling
Recrystallized microstructure in single-crystal CMSX-4 sample after tensile testing at approximately 1290°C and annealing at 1300°C for 19h.
PhD defence of Yijian Wu
13 December 2022
Yijian Wu defends his PhD in Computational Mechanics and Materials on Dec. 13, 22
Developments and applications of a multi-scale numerical method coupling the Cellular Automaton and Parabolic Thick Needle methods for the prediction of dendritic grain structures
Yijian Wu conducted his PhD work under the supervision of Charles-André Gandin and Oriane Senninger (2MS team). He defends his PhD in "Computational Mechanics and Materials" on December 13, 22 (subject to the agreement of the reviewers) in front of the following jury:
– Mr Henri Nguyen-Thi, Aix-Marseille Université, Reviewer
– Mrs Olga Budenkova, SIMaP, Reviewer
– Mr Mathis Plapp, Ecole Polytechnique, Laboratoire de Physique de la Matière Condensée
– Mr Charles-André Gandin, CEMEF Mines Paris – PSL
– Mrs Oriane Senninger, CEMEF Mines Paris – PSL
Abstract:
Numerical methods for modeling the microstructures formed during solidification are of great academic and industrial interest. The Cellular Automaton – Parabolic Thick Needle (CAPTN) method is a multiscale numerical method, which couples the Cellular Automaton (CA) and the Parabolic Thick Needle (PTN) methods, to simulate the growth of dendritic grains while accounting for non-steady diffusion fields. A dendritic branch is modeled as a cylinder headed by a parabolic tip. Its kinetics is computed using the PTN method from the composition field in the liquid in the vicinity of the parabola. This dendritic branch takes part in the definition of a grain envelope by its integration in a CA growth algorithm.
This thesis presents advances and computing optimizations on the multiscale CAPTN method. Indeed, at the beginning of the thesis, the CAPTN method was only implemented in two dimensions and was not numerically efficient. An adaptive heterogeneous meshing strategy and the orthogonal query method with the octree structure are therefore employed on the finite element implementation of the PTN method for increasing computational efficiency. The three-dimensional implementation of the PTN method is performed and evaluated through the analyses of convergence of simulation results to theoretical solutions depending on numerical parameters. Algorithmic improvements on the PTN method and the CAPTN coupling are also performed. The optimized three-dimensional CAPTN model is evaluated by modeling an equiaxed grain growing under constant supersaturation. The kinetics obtained by the CAPTN model is in good agreement with the kinetics obtained by the Phase-Field (PF) model and the Dendritic Needle Network (DNN) model. The optimized two-dimensional CAPTN model is evaluated on its ability to reproduce two physical quantities developed during directional growth in a constant thermal gradient with constant isotherm velocity: the primary dendritic arm spacing and the grain boundary orientation angle between two grains of different orientations. It is shown that the CAPTN model can reproduce the grain selection between primary branches and creation of new branches from tertiary branches as long as cell size is sufficiently small to model solute interactions between branches. In these conditions, simulations converge toward a distribution of primary branches which depends on the history of dendrite branches, in agreement with experimental results and theory. Contrary to the classical CA model, the grain boundary orientation angle obtained in CAPTN simulations is stable with cell size and in good agreement with previous PF studies for various temperature gradients.
Keywords: solidification, modeling, multi-scale, Cellular Automaton, Parabolic Thick Needle, dendritic microstructure
Solidification front of the bi-crystal CAPTN simulation, presented by (a) needle network, (b) composition field in PTN finite element mesh, and (c) automaton cells
PhD defence of Sacha El Aouad
9 December 2022
Sacha El Aouad will defend his PhD in Computational Mathematics, High Performance Computing and Data on Dec. 9, 22.
Numerical and parallel modeling of anisotropic fitted mesh for industrial quenching applications.
Sacha El Aouad conducted her PhD work in the CFL team under the supervision of Elie Hachem and Aurélien Larcher. She will defend hers PhD in Computational Mathematics, High Performance Computing and Data, on December 9, 22 in front of the following jury:
– Suzanne Michelle Shontz, University of Kansas
– Joan Baiges, Universitat Polytècnica de Catalunya
– Johan Hoffman, KTH, Royal Institute of Technology, Suède
– Giulia Lissoni, SCC Consultants
– Elie Hachem, Mines Paris – PSL, CEMEF
– Aurélien Larcher, Mines Paris – PSL, CEMEF
Abstract:
The development of efficient methods to simulate multi-components systems is among engineering challenges and still a need for industrials, especially in the case of fluid-structure interaction or conjugate heat transfer. The quenching process falls within this framework since it impacts directly the change in the mechanical and physical property of industrial parts. Many numerical formulation of this process have been developed, but considerable imprecision still exists, especially because of the assumptions made on the use of simple geometries and approximate quench environments. For the quenching process, several types of geometries with different complexities are studied and analyzed. Therefore, generating meshes for such complex geometries is a challenge. By improving methods for multi-physics, particularly fluid-thermal and fluid-solid couplings, the overall mathematical framework of this thesis will address this challenge.
In this work, the Immersed Volume Method is extended: a new anisotropic adaptive body-fitted mesh method is proposed. Its simplicity and generality allow it to tackle complex geometries, and its robustness allow to deal with complex physical problems. Two successive iterations are combined: first, gradient-based metric construction uses the gradients of the level-set function of any immersed object to generate an anisotropic well-adapted mesh. It is followed by a geometric adaptation using R-adaptation and swapping in order to create a sharp fitted mesh. This new approach achieves the desired local geometry resolution of a body-fitted mesh and obtains the needed numerical accuracy at the interface due to the anisotropic unstructured elements.
The new approach will allow to solve fluid-solid interactions and CFD problems including boundary layer, curvature, and high-gradient solutions, covering 2D and 3D parallel applications, and real-world practical problems.
Keywords: Immersed methods, Anisotropic Adaptation, Numerical modelling, Fitted Mesh, Level-set function, CFD
PhD defence of Victor Grand
5 December 2022
Victor Grand defends his PhD in Computational Mechanics and Materials on Dec. 5th, 22
"Characterization and modeling of zircaloy-4 recrystallization during hot forming"
Victor Grand conducted his PhD work under the supervision of Marc Bernacki (MSR team). He defends his PhD in "Computational Mechanics and Materials" on December 5, 22 (subject to the agreement of the reviewers) in front of the following jury:
M. Lukasz MADEJ, AGH University of Science and Technology, Reviewer
M. Javier SIGNORELLI, Instituto de Fisica Rosario, Reviewer
M. Frank MONTHEILLET, Mines de Saint-Étienne
M. Pierre BARBERIS, Framatome, CRC
M. Alexis GAILLAC, Framatome, CRC
Mme Nathalie BOZZOLO, CEMEF, Mines Paris, Université PSL
M. Baptiste FLIPON, CEMEF, Mines Paris, Université PSL
M. Marc BERNACKI, CEMEF, Mines Paris, Université PSL
Abstract:
Due to their low neutron-capture cross-section, their good mechanical properties and their resistance to corrosion, zirconium alloys are used in nuclear industry for several decades. The manufacturing processes are complex and include several deformation and heat treatment stages. Each of these steps must fulfill two criteria: getting closer to the final product shape without any defect and provide to final product a microstructure suited to withstand the severe conditions in nuclear reactors. Consequently, and to fulfill the high security requirements of nuclear industry, it is necessary to understand and master the microstructure evolution during the forming and heat treatment processes. Moreover, the development of predictive numerical tools at the mesoscopic scale is thus of paramount importance.
To that end, many hot deformed microstructures were characterized by EBSD to determine the impact of thermomechanical conditions and of initial microstructure upon microstructure evolution of zircaloy-4. These data have been compared to full-field simulation results at the mesoscopic scale. To do so, Gourdet-Montheillet laws were introduced into a Level-Set model, embedded into a finite element framework and the results validated. This implementation enables to simulate continuous recrystallization mechanisms for dynamic and post-dynamic conditions and thus to improve the model ability to simulate recrystallization of zircaloy-4. Experiment and simulation results have enabled to quantify the influence of initial microstructure and to discriminate which microstructural features condition the observed mechanisms. The current limitations of the developed approach were also discussed.
Keywords: Hot forming, Zirconium alloys, Recrystallization
