Labex

Achievements

One of the main objectives of metallurgical processes is to improve the properties of metals by changing their microstructure. This is readily possible by imposing extremely large plastic deformation on the metal. SPD enables an enormous reduction in grain size which can multiply the strength of the material up to an order of magnitude.

A success story in the application of SPD in the Labex DAMAS is to use it for metal powder compaction to introduce polymer into the metal, then converting the polymer into nano-size ceramics by pyrolysis. Such polymer-derived ceramic-reinforced matrix-metal composite is nano-structured, has high microstructure stability, and heat resistant. The process is worldwide patented in collaboration with the Indian Institute of Science, Bangalore.

Learn more: Laszlo Toth, Satish Vasu Kailas, Yajun Zhao, Abhishek Pariyar, Marc Ponçot, Marc Novelli, and Viet Quoc Vu. Metal matrix polymer derived ceramic composites, processes of production and uses thereof. Worldwide patent no. WO2022194938, 2022.

Structural refinement down to the submicrometric scale is an efficient method to increase the mechanical strength of metallic materials. It can be achieved by using severe plastic deformation (SPD) techniques, in particular at the surface (SSPD) of the material were numerous damaging processes can take place. By creating a gradient microstructure, SSPD modifies for example (i) the material integrity for fatigue as well as (ii) the material reactivity for corrosion or for improving thermo-mechanical surface treatments.

• One of the approaches developed by the laboratory is to use temperature during SSPD as an influent processing parameter. We have developed devices authorizing intense shot peening in a temperature range going from cryogenic to 500°C. The associated figure shows the image furnace developed for warm surface mechanical peening treatments.
• Through collaborations and PhD supervisions with LOFPA (ETS – Montréal – Canada) and Pprime (Poitiers – France) we have for example shown the interest of these treatments “in temperatures” for improving the fatigue life of stainless steels as well as a range of Al and Ti based alloys.

Learn more: C. Dureau, M. Arzaghi, R. Massion, Y. Nadot, and T. Grosdidier. On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: effect of load ratio and associated residual stress modifications. Materials Science and Engineering A 840, 142916, 2022.

Plasma-assisted electrochemical surface treatments, including plasma electrolytic oxidation (PEO), plasma electrolytic nitriding (PEN)/carburizing (PEC) and plasma electrolytic polishing (PEP), are technologies in which micro-plasma discharges appearing in an aqueous solution are used to chemically modify the processed metal surfaces (see image). The PEO process for example allows the rapid growth of protective oxide coatings on lightweight metals (Al, Mg, Ti).

• In collaborations with Saarland University (Germany) and ITMO University (Russia), one of the approaches developed in the laboratory is to combine in situ optical and electrical measurements of the process together with ex situ microstructural characterizations of the ceramic coatings in order to improve our understanding of the mechanisms of oxidation to make the PEO process more efficient.

  Learn more: J. Martin, A. Nomine, V. Ntomprougkidis, S. Migot, S. Bruyère, et al. Formation of a metastable nanostructured mullite during Plasma Electrolytic Oxidation of aluminium in “soft” regime condition. Materials & Design, 2019.

• More recently, with ICB (France), duplex treatments combining cold-spraying with PEO were investigated as a new route to prepare ceramic-based composite coating on a wider variety of metals.

  Learn more: A. Maizeray, Grégory Marcos, Andrea Cappella, Marie-Pierre Planche, H. Liao, et al. Effects of dispersed α-Al2O3 particles into a cold-sprayed aluminium coating on its subsequent oxidation by the PEO process. Surface and Coatings Technology, 2024.

Excessive fossil fuel consumption and resultant greenhouse gas emissions have led to public health and environmental deterioration at a global level. Towards an ecological energy transition, hydrogen has become one of the most promising because it possesses the highest gravimetric energy density (142 MJ.kg−1) among energy carriers. Its effective development mainly needs to solve three scientific problems: (i) the hydrogen green production, (ii) its high-density storage and transportation, (iii) an efficient conversion of hydrogen.

• Solid-state hydrogen storage in the form of metal-hydrides is a promising technic to safely store a high quantity of hydrogen. However, the storage material usually requires to be activated under a high temperature and dynamic vacuum to ensure the initial hydrogen absorption (activation).
• In collaboration with scientist at the University of Kyushu in Japan, it has been demonstrated on Ti-V-Cr alloys that surface severe plastic deformation results in a gradient microstructure where microstructural defects and ultra-fine grains at the surface allows to activate the material at room temperature while the hydrogen reversibility is ensured via the formation of hydrides in the undeformed core of the sample. The associated figure gives a sketch of the gradient microstructure and how the H atoms interact.

Learn more: M. Novelli, K. Edalati, S. Itano, HW. Li, E. Akiba, Z. Horita, and T. Grosdidier. Microstructural details of hydrogen diffusion and storage in Ti–V–Cr alloys activated through surface and bulk severe plastic deformation. International Journal of Hydrogen Energy 45 (8), 5326-5336, 2020.

The carbide-free bainitic microstructures in steels enable exceptional mechanical performance in terms of the compromise between strength, ductility, and formability. These steels belong to the so-called Third-Generation of AHSS (Advanced High Strength Steels) for automotive structures. Our work conducted on synchrotron beamlines allowed us to study in situ, using high-energy X-ray diffraction, the fine mechanisms of bainitic transformation and to establish precise carbon balances at the phase scale. These balances were validated by two other direct measurement techniques, namely atom probe tomography and transmission electron microscopy (energy loss spectroscopy), conducted as part of collaborations with GPM in Rouen, France and CANMet in Hamilton, Canada.

Figure 1 represents a 2D diffractogram acquired in situ and Figure 2 the set-up at DESY, Petra III (P07 beamline), Hambourg, Germany.

Learn more: I. Pushkareva, J. Macchi, B. Shalchi-Amirkhiz, F. Fazeli, G. Geandier, F. Danoix, C. Scott, et al. A study of the carbon distribution in bainitic ferrite. Scripta Materialia, 2023.

Polymer core metal sandwiches are known for their excellent Ashby-specific stiffness, but they also offer acoustic damping capabilities for the automotive industry. The two roadblocks well identified for their development and industrialization are resistive welding and adhesion between polymer and metal.

In this particular study, we presented an identification method on the vibration properties of a periodic core sandwich considering the thermal impact on the band gap. Periodic sandwich beam samples were elaborated and vibration tests were performed under thermal conditions and compared to the results obtained from our robust finite element method. The experimental results showed good agreement with the numerical simulations. The sandwich beams demonstrated a filtering behaviour with the presence of band gap for a specific temperature range. The critical temperature is the glass transition temperature of the soft viscoelastic core material which represent the minimum temperature for the use of sandwich composites with a periodic structure.

Learn more: T. Huchard, G. Robin, M. Ponçot, S. Hoppe, and E.M. Daya. Elaboration, Characterization and Modelling of Periodic Viscoelastic Sandwich Beams for Lightening and Vibration Damping. Mechanics Research Communications, 121, 103863, 2022.

The behavior of lightweight porous materials under shock loading involves complex multi-scale interactions, spanning from the macroscale geometry to the microscale pores. Experimental investigations, using plate impact experiments on closed-cell porous aluminum obtained using AM techniques, have, for the first time, highlighted the essential role of micro-inertia in defining the shock structure in these materials. This work was conducted, as part of a collaboration with Caltech, USA. Additionally, finite element calculations have revealed the influence of the porous structure (size, shape, and spatial distribution of voids) in shaping the shock front and influencing the plastic shock width.

Figure 1 presents a steady shock wave propagating in a porous material and a schematic of the radial acceleration fields (micro-inertia effects) in the dynamic collapse of pores. Figure 2 presents the plastic shock width, w, with respect to the void aspect ratio λV for two families of axisymmetric unit cells used to build the Finite Element modeling (F*: fixed cell size, F+: fixed void axial length).

Learn more:

• E. Massarwa, C. Czarnota, A. Molinari. Finite Element Modeling of steady plastic shockwaves in porous metals: Role of size, shape, and spatial distribution of voids. International Journal of Impact Engineering, 184, 104817, 2024.
• Z. Lovinger, C. Czarnota, S. Ravindran, A. Molinari, G. Ravichandran. The role of micro-inertia on the shock structure in porous metals. Journal of the Mechanics and Physics of Solids, 154, 104508, 2021.

A novel Digital Image Correlation technique is applied on EBSD pattern to map disorientations with High angular Resolution, as well as geometrically necessary dislocation densities and elastic strains. The performances of the developed HR-EBSD method are illustrated on orientation maps acquired on advanced steel microstructures. The new method is implemented in ATEX software.

Learn more: C. Ernould, B. Beausir, J-J. Fundenberger, V. Taupin, and E. Bouzy. Global DIC approach guided by a cross-correlation based initial guess for HR-EBSD and on-axis HR-TKD. Acta Materialia 191, 131-148, 2020.

A new SEM-based set-up for orientation data acquisition called “on-axis” Transmission Kikuchi Diffraction (on-axis TKD) was developed. It makes grains and twins below 10 nm well visible in orientation maps and with high indexation rate, as demonstrated with an electrodeposited nanocrystalline Ni.

Learn more: E. Brodu, E.l Bouzy, J-J Fundenberger, et al. On-axis TKD for orientation mapping of nanocrystalline materials in SEM. Materials Characterization, 130, 92-96, 2017.

A U-Net model was trained to perform the segmentation of bainite, ferrite and martensite on EBSD maps using the kernel average misorientation and the pattern quality index as input. The model outperforms human performance: 92% of accuracy are obtained in few seconds.

Learn more:

• S. Breumier et al. Leveraging EBSD data by deep learning for bainite, ferrite and martensite segmentation. Materials characterization, 2022.
• T. Martinez Ostormujof et al. Deep Learning for automated phase segmentation in EBSD maps. A case study in Dual Phase steel microstructures. Materials Characterization, 2021.

A numerical implementation of a non-local polycrystal plasticity theory based on a phenomenological mesoscale field dislocation mechanics theory (PMFDM) was developed with the elastoviscoplastic fast Fourier transform-based (EVPFFT) formulation.

In addition to considering plastic flow and hardening only due to SSDs (statistically stored dislocations) as in the classic EVPFFT, the proposed method accounts for the evolution of GND (geometrically necessary dislocations) densities, and GND effects on both plastic flow and hardening. This allows consideration of an enhanced strain-hardening law that includes the effect of the GND density tensor. The numerical procedure is used to perform full field simulations of polycrystal plasticity considering different grain sizes and their mechanical responses during monotonic tensile and reversible tension-compression tests. Using Voronoi tessellation and periodic boundary conditions, representative volume elements (RVEs) with different grain sizes were generated.

A Hall-Petch type scaling law is obtained (see Figure). For reversible plasticity, a strong Bauschinger effect is observed with the PMFDM-EVPFFT approach, in comparison with conventional EVPFFT. The origin of these differences is analyzed in terms of plastic heterogeneities, GND density and stress evolutions during the compression stage.

Learn more: S. Berbenni, V. Taupin, and R.A. Lebensohn. A fast Fourier transform-based mesoscale field dislocation mechanics study of grain size effects and reversible plasticity in polycrystals. Journal of the Mechanics and Physics of Solids, 135, 103808, 2020.