Congratulations to Étienne Carré for winning the ONERA 2021 thesis prize in the “Materials and Structures” field. This prize, awarded each year by senior ONERA researchers, aims to encourage future researchers on the path to excellence and to recognize remarkable work. Etienne’s presentation entitled “Infrared luminescence based on black phosphorus” is available here (https://www.youtube.com/watch?v=sIL6nHMUmLM&t=7s). His work is carried out within the framework of the ANR17-CE24-0023 EPOS-BP research project involving the LEM (UMR ONERA / CNRS), GEMaC (UMR UVSQ / CNRS), UMPhy (UMR THALES / CNRS) and THALES TRT laboratories.
LEM, UMR ONERA-CNRS – SIAM, ONERA
Additive Manufacturing is arousing great interest in both academic and industrial communities, in particular with a view to reducing raw material waste and optimising manufactured components. During the internship carried out between the SIAM unit of DMAS/ONERA and the LEM (CNRS/ONERA), particular attention was paid to the impact of thermal hardening on the precipitation of intermetallic phases in the aluminum alloy Al-4Fe, manufactured by Laser Powder Bed Fusion (L-PBF). First, an experimental study at different scales was carried out in order to characterise the microstructure of the Al-4Fe material in its metallurgical state after fabrication. Various manufacturing conditions were studied. The grain microstructure as well as the precipitation of iron-rich phases were studied by different microscopy techniques (optical, SEM, TEM). Secondly, the evolution of the hardness and the modifications of the microstructure induced by various post-manufacturing heat treatments were characterised. The small disorientations inside the grains were measured by EBSD in order to obtain information on the strain hardening of the material during these treatments. Finally, the various contributions necessary for the development of a model of the hardness of these alloys were discussed.
Tuesday 28th September 2021 at 9h30
videoconference at the followink link: https://rdv.onera.fr/seminaireLEM
LEM, UMR ONERA-CNRS
At the nanoscale, nanomaterials possess unique properties that differ strongly from those of the bulk material. In the case of AgPt nanoparticles, we aimed to study the solid-liquid transition of nanoparticles of different sizes and compositions. For this purpose, we performed atomic scale simulations using a semi-empirical potential integrated in a Monte Carlo code to relax the structures. In doing so, we observed that the melting temperature decreases with the size of the nanoparticles (pure systems and alloys). However, our detailed analysis shows that the melting of the nanoparticle systematically passes through an intermediate stage with a crystalline core (pure Pt or AgPt depending on the composition) and a layer of liquid Ag.
Thursday 29th July 2021 at 11h00
videoconference at the following link: https://cnrs.zoom.us/j/98877547159
It is with great sadness that we have learned of the sudden death of our colleague François Ducastelle, which happened on Friday 2 July 2021.
François joined ONERA in 1965 as a trainee and was hired as junior scientist in 1968. He prepared his two theses and spent his entire career as a researcher. From 1981 to 1997, he was head of the Solid State Physics Division in the Materials Directorate (OM), then was deputy director of the LEM until his emeritus in 2008.
An outstanding physicist, François has had a profound impact on the many disciplinary fields he has tackled: the electronic structure of metals and their alloys, the statistical physics of order-disorder and phase transitions, growth modes and spectroscopic properties of low-dimensional materials.
Through the extensive nature of his work, his involvement in the management of the LEM and his enthusiasm for research, François has made a major contribution to shaping the laboratory of today and to its influence.
All those who have worked with François, from the doctoral students he trained to the many colleagues he guided and who came to him for advice and enlightenment, testify to the wide range of his knowledge, the depth of his analysis, the power and elegance of his reasoning, his teaching skills and his benevolence.
Always active and involved in numerous projects, François maintained a dynamic of collective research and numerous interactions with the international scientific community. He also interacted with young researchers on a daily basis, with great humility and humanity.
A great physicist has passed away. His memory and his teaching remain.
His death leaves a lot of sadness and a big void in the laboratory.
Our thoughts are with his family and friends, to whom we offer our sincere condolences.
Mathieu Fèvre (Mathieu.Fevre@onera.fr) is the point of contact for information about the funeral and for expressions of support to his family.
Testimonies, tributes and memories of our colleague François can be posted at the following link : https://hommage.uneroseblanche.fr/odoklp
Dr. Enrica Epifano
CIRIMAT, UMR 5085, toulouse France
In this talk, E. Epifano will present the results of her postdoctoral research conducted at the ONERA. The presentation will comprise two parts. In the first part, solubility and diffusion of light atoms (B, C, N, O) in the γ-TiAl intermetallic phase are investigated by first-principle calculations. The accommodation of the light atoms in the various interstitial positions is studied by density functional theory. Barrier energies for their diffusion among the different interstitial sites are computed using the Nudged Elastic Band (NEB) method and atomic jumping rates are obtained from the Transitional State Theory. Diffusion coefficients are obtained from the solution of the transport equation in the infinite time limit, using the analytical Multi-State Diffusion method.
In the second part, experimental studies of the oxidation resistance of MAX phases are shown. The MAX phases are a new class of materials that have an extraordinary combination of both metallic and ceramic features. Some of the MAXes are alumin-forming and they hence exhibit excellent oxidation resistance. The results herein shown concern a study on the quaternary (Tix,Ga1-x)3AlC2 phase, realized in collaboration with the Drexel University of Philadelphia.
Friday 25 June 2021 14h00
videoconference at the following link: https://rdv.onera.fr/seminaireLEM
Viviane Laut-Cothias, our executive assistant, was a person who gave the best of herself, with a constant desire to be useful to everyone. She was very careful with others and radiated great kindness. Her departure leaves a great void and a lot of sadness.
Dr. Antoine GUITTON1,2
1Université de Lorraine – CNRS – Arts et Métiers – LEM3, Metz, France
2LabEx Damas – Université de Lorraine, Metz, France
Although mechanics of materials is aged by more than one century, it still faces many conceptual challenges. One must relate two extreme scales: the sample scale (i.e. Macroscopic) and the scale of fundamental mech- anisms (i.e. Microscopic). In addition, statistics of observations are generally extremely low so that, on one hand the uncertainty is high and on the other hand the representativeness of mechanisms is very questionable.
The Transmission Electron Microscope (TEM) is one of the most well-known techniques for observing and characterizing dislocations in electron transparent thin foils (thickness of ≈ 100nm with a useful field of view of few μm) (1–4). Comprehensive dislocation studies at microscopic scale bring valuable information for extrapolating to the macroscopic mechanical response of materials and they can feed numerical advanced multiscale crystal plasticity models (4). However, fundamental questions on the representativeness of observed phenomenon must be raised, when extrapolating discussions to a millimeter-size specimen.
In this framework, we have successfully combined mechanical testing (nanoindentation and in-situ tensile tests) of bulk specimens with a dislocation-scale characterization technique: Accurate Electron Channeling Contrast Imaging (A-ECCI) (5). A-ECCI is a non-destructive procedure offering the ability to provide, inside a Scanning Electron Microscope (SEM), TEM-like diffraction contrast imaging of sub-surface defects (at a depth of about 100 nm) on centimetric bulk specimen with still unsurpassed resolutions (6).
First, physics of defect contrasts and experimental procedures will be presented (5; 7; 8). Second, the full potentiality of A-ECCI for following the evolution of deformation microstructures will be detailed (9–11). Finally, statistical comparisons between crystal plasticity models and experiences will be highlighted in the framework of a first step towards feature engineering (12–14).
Thursday 27 May 2021 14h00
videoconference at the following link: https://rdv.onera.fr/seminaireLEM
 G.P. Bei, A. Guitton, A. Joulain, V. Brunet, S. Dubois, L. Thilly, and C. Tromas. Pressure-enforced plasticity in MAX phases: from single grain to polycrystal investigation. Philosophical Magazine, 93(15):1784–1801, may 2013, doi: 10.1080/14786435.2012.755272, hal-hal-01501851.
 A. Guitton, A. Joulain, L. Thilly, and C. Tromas. Dislocation analysis of Ti2AlN deformed at room temperature under confining pressure. Philosophical Magazine, 92(36):4536–4546, dec 2012, doi: 10.1080/14786435.2012.715250, hal-03041046.
 A. Guitton, A. Joulain, L. Thilly, and C. Tromas. Evidence of dislocation cross-slip in MAX phase deformed at high temperature. Scientific Reports, 4(1):6358, may 2015, doi: https://doi.org/10.1038/srep06358, hal-01503720.
 K. Gouriet, P. Carrez, P. Cordier, A. Guitton, A. Joulain, L. Thilly, and C. Tromas. Dislocation modelling in Ti2AlN MAX phase based on the Peierls–Nabarro model. Philosophical Magazine, 95(23):2539–2552, aug 2015, doi: 10.1080/14786435.2015.1066938, hal-01515323.
 H. Kriaa, A. Guitton, and N. Maloufi. Fundamental and experimental aspects of diffraction for characterizing dislocations by electron channeling contrast imaging in scanning electron microscope. Scientific Reports, 7(1):9742, aug 2017, hal-02392256.
 J. Guyon, H. Mansour, N. Gey, M.A. Crimp, S. Chalal, and N. Maloufi. Sub-micron resolution selected area electron channeling patterns. Ultramicroscopy, 149:34–44, feb 2015, doi: 10.1016/j.ultramic.2014.11.004, hal-01514962.
 H. Kriaa, A. Guitton, and N. Maloufi. Modeling dislocation contrasts obtained by Accurate-Electron Channeling Contrast Imaging for characterizing deformation mechanisms in bulk materials. Materials, 12(10):1587, may 2019, doi: 10.3390/ma12101587, hal-02392249.
 H. Kriaa, A. Guitton, and N. Maloufi. Modelling Electron Channeling Contrast intensity of stacking fault and twin boundary using crystal thickness effect. Materials, 14(7):1696, mar 2021, doi: 10.3390/ma14071696, hal-03118996.
 A. Guitton, H. Kriaa, E. Bouzy, J. Guyon, and N. Maloufi. A dislocation-scale characterization of the evolution of deformation microstructures around nanoindentation imprints in a TiAl alloy. Materials, 11(2):305, feb 2018, doi: 10.3390/ma11020305, hal- 02392252.
 M. Ben Haj Slama, N. Maloufi, J. Guyon, S. Bahi, L. Weiss, and A. Guitton. In situ macroscopic tensile testing in SEM and Electron Channeling Contrast Imaging: pencil glide evidenced in a bulk β-Ti21S polycrystal. Materials, 12(15):2479, aug 2019, doi: 10.3390/ma12152479, hal-02392248.
 F. Habiyaremye, A. Guitton, F. Sch ̈afer, F. Scholz, M. Schneider, J. Frenzel, G. Laplanche, and N. Maloufi. Plasticity induced by nanoindentation in CrCoNi medium-entropy alloy studied by accurate electron channeling contrast imaging revealing dislocation-low angle grain boundary interactions. Accepted in Materials Science and Engineering: A, 2021, hal-03118990.
 M. Ben Haj Slama, V. Taupin, N. Maloufi, K. Venkatraman, A.D. Rollett, R.A. Lebensohn, S. Berbenni, B. Beausir, and A. Guitton. Electron channeling contrast imaging characterization and crystal plasticity modelling of dislocation activity in Ti21S BCC material. Materialia, page 100996, mar, doi: 10.1016/j.mtla.2020.100996, hal-03094460.
 K. Venkatraman, M. Ben Haj Slama, V. Taupin, N. Maloufi, and A. Guitton. Tuning critical resolved shear stress ratios for BCC- Titanium Ti21S via an automated data analysis approach. 2021, hal-03119000.
 F. Habiyaremye, A. Guitton, X. Lei, T. Richeton, S. Berbenni, G. Laplanche, and N. Maloufi. Influence of the local dislocation density and configuration on the first pop-in load during instrumented nanoindentation. 2021.
First synthesised in the 60’s, the metallic glasses are a very promising class of material thanks to their very high yield strength. Yet, these materials are also very brittle due to the formation of persistent shear bands which concentrate plastic deformation.
In this thesis, we perform atomistic simulations with a simple two-dimensional binary Lennard-Jones model glass. To link plasticity and the material structure, we use a novel structural indicator, the local yield stress.
Through this measure, the material average local yield stress is shown to increase as the degree of relaxation increases. We also find the existence of a unique post-yield shear threshold distribution, independent on the initial state of the material.
By the mean of an elementary model, the origin of the Bauschinger effect in amorphous solids (a plasticity-induced asymmetry of the mechanical behaviour) is found to arise from the inversion of the low yield barriers population anisotropy during the unloading.
Then, by considering systems of different sizes and degrees of relaxation the persistence of plasticity, and thus the formation of shear-bands, is shown to mostly depend on the degree of relaxation of the system.
Finally, in well relaxed glasses, a correlation between the location of the shear band and the initial soft regions is shown. As further loading is applied on the material, a diffusive broadening of the shear band is observed.
Due to the strong correlation between chemical order and physical properties, nanoalloys with a tendency to order are particularly interesting in the field of catalysis, magnetism, or optics. By reducing the size of the system, i.e. from a solid alloy to a nanoalloy, many questions arise: Is the chemical order preserved? What is the morphology of nanoparticles? What is the composition and chemical order on the surface? What is the evolution of properties with size? This presentation is devoted to the study of two systems, both similar and different in their behavior: Co-Pt, a system emblematic of the chemical order, and Pt-Ag, a hybrid system presenting both a chemical order and a tendency to demix, as well as a strong tendency to segregation. In order to answer these various questions, we adopt a semi-empirical approach through an N-body potential, allowing atomic relaxations, in the approximation of the second moment of state density (SMA), coupled with Monte Carlo simulations in different ensembles. The SMA potential is adjusted, in order to reproduce the volume and surface properties, on calculations derived from the theory of density functional theory (DFT) or on experimental data. In a first step, the volume phase diagram of the two systems is determined by the model and compared to the experiment. Then the low index surfaces (111), (100) and (110) are studied in order to verify the segregation inversion observed for the Co-Pt system, where Pt segregates weakly on the dense surfaces (111) and (100) but where we observe a pure Co plane on the surface (110). On the contrary, the Pt-Ag system shows strong Ag segregation on surfaces (111) and (100). In a second step, aggregates of truncated octahedral morphology of different sizes (ranging from 1000 to 10000 atoms) will be analyzed in terms of chemical composition on the different unequal sites (top, edge, facets (100) and (111) and core) and then compared to the reference systems (surfaces, volume) over the whole concentration range. For the Co-Pt system, we observe ordered structures similar to those of the volume for the core and similar to those of the surfaces for the facets. The impact of the two-dimensional phase (√3 × √3)R30◦ specific to the surface, is all the more important on the chemical order at the core as the nanoparticle is small. For the Pt-Ag system, we observe an important segregation of Ag at the surface, as well as a Pt enrichment at the subsurface, and the stabilization of the L11 ordered phase at the core. This structure can appear in a single variant or by adopting all possible variants, leading to an onion peel structure.
Scientists of LEM, LP2N (France), Polytechnique Montréal, Université de Montréal (Canada) have succeeded in encapsulating organic dye molecules inside a boron nitride nanotube. This encapsulation protects efficiently organic dye molecules against degradations inherent to their surrounding conditions and improves the fluorescence over a time scale longer by 104 with respect to that of free dyes.
More details on the of CNRS INP website.