The aim of the HoTMiX academic research project is to provide a deep understanding of the relationships between the nonlinear mechanical response of oxide materials at very high temperature and their microstructure at the nanoscale. During elaboration, or operando conditions, solid-state phase transitions (SPTs) associated with highly anisotropic elastic behavior and thermal expansion induce a complex mechanical response that still remains to be studied (and eventually tailored). Relaxation of thermal stresses through SPTs results in the formation of microstructures that usually involve length scales spanning at least three orders of magnitude from the crystal to the grain size. Indeed, coherently diffracting domains have a typical size of few tens of nanometers and they are part of larger crystalline areas of usually a few tens of micrometers. A striking feature of these oxide materials lies in the huge (three orders of magnitude) difference between local stresses within coherent domains (nm scale), which are in the GPa range, and the tensile strength of the bulk (i.e. cm scale), usually of only a few tens of MPa. On top of that, the temperature range in which relevant phenomena take place (stress build-up, microcracking, and SPTs) span from room temperature to 2000 °C, thereby covering three orders of magnitude. Therefore, the general question that we want to address requires a multiscale analysis along three main axes: temperature, stress, size. Combining plasticity at the microstructural scale with unconventional elastic behavior, related to size effects, some intrinsically brittle oxide materials exhibit an unexpected high compliance. Although this is observed at the microscale, its origin lies at the nanoscale. The understanding at the nanoscale of this mechanical behavior, is the central objective of the HoTMiX project. Using several X-ray based advanced techniques (scattering, diffraction, refraction, tomography) at synchrotron radiation beamlines, we will determine the microstructure evolution (in situ at very high temperatures and/or under applied stresses) of these “living oxide materials”. This is the main experimental challenges that we will address in the HoTMiX project. The relationship between microstructure and mechanical properties will be explored by combining in situ quantitative experimental measurements at very high temperature and/or under applied stresses with accurate microstructural modelling based on virtual but realistic microstructures submitted to temperature and external stresses evolutions.

New innovative and advanced materials are needed to develop robust, safe and cost-effective infrastructures for hydrogen distribution or storage. BYRON will focus on the fabrication of multilayered structures composed of two semi-crystalline polymers that can serve as innovative materials for polymer liners (or membranes) in high-pressure gaseous systems (tubes or type IV/type V pressure vessel). The use of an innovative layer-multiplying coextrusion process, specially designed for annular geometries like tubes, will allow the creation of a high number of alternating thin layers. The impact of this nanolayering on the crystalline structure will be characterized and correlated with hydrogen permeability and mechanical properties. The behavior of the multi-nanolayered structures will be investigated in conditions close to the actual working conditions of the hydrogen storage tank (effect of hydrogen exposure and high-pressures), using specific permeation equipment and mechanical tests. In particular, failure modes and sensitivity to blistering will be thoroughly studied. Finally, a numerical diffusion model will be developed in order to assess the impact of the geometrical parameters on the permeation and used as a predictive tool for guiding the development of optimized multilayered architectures.

The objective of this pathfinder and interdisciplinary MIRACLES project is to draw on the knowledge inferred from bi-crystalline plasticity in face-centered cubic metals (bi-crystallography, slip/grain boundary interactions) in order to guide by geometrical analogues the manufacturing of new tailored bi- or oligo-crystalline microtrusses with disoriented meta-grains having different strut connectivities at the interface between meta-grains. Numerical simulations performed with Finite Elements (FE) for microtrusses, and analytical/ numerical fast Fourier transform (FFT) for advanced bi-crystal/ oligo-crystal plasticity respectively, will be guided with artificial intelligence (AI) methods, to propose analogues and conceptual transfers between both disciplines. Thanks to these analogues, the idea is to make emerge new tailored structures of microtrusses in terms of damage tolerance able to delay or eliminate the occurrence and the propagation of shear bands responsible for the global collapse of the structure. It is expected that these new architected bi-crystalline and oligo-crystalline microtrusses allow a better energy absorption capacity than single lattice structures. The bi- and oligo-crystalline microtrusses will be obtained by additive manufacturing process of a 316L steel based on powder bed fusion. Compressive tests with 2D and 3D image correlation during deformation will be conducted in order to quantify strain localization and validate the scientific approach. The project will result in the proposition of damage-tolerant microtrusses regarding energy absorption.

Additive manufacturing by laser powder bed fusion (LPBF) is gaining increasing significance within the aeronautics and automotive sectors for the production of complex metal components. While aluminum alloys are appealing due to their high specific strength, certain grades are highly susceptible to hot cracking, presenting challenges in LPBF manufacturing. The DALAILAMA project aims to develop a specialized aluminum alloy for the LPBF process, focusing on three primary objectives. First and foremost, a novel alloy will be designed to minimize the risk of cracking while achieving a more uniform and controlled microstructure, thus striking a balance between strength and ductility. This will involve the precise management of nucleating agents and the control of precipitates formation in terms of both fraction and kinetics. In the subsequent phase, model alloys will be selected and produced by atomization and powder mixing to quickly test the design criteria. Instrumented LPBF manufacturing tests will highlight the impact of alloy composition on the stability of the meltpool and on the spatters emission. Finally, the selected optimal composition will be produced on a larger scale by atomization and processed by LPBF. Mechanical and microstructural assessments will be conducted to evaluate its performance and in-use properties. This project aims to establish a novel methodology for designing alloys suitable for the LPBF process, including both innovative experimental techniques and a digital optimization framework. It will also lead to the creation of a high-performance aluminum grade dedicated to LPBF. These advances will drive the development of lightweight aluminum grades for industry, offering both new design tools and higher performance materials.

During the last decades, the principal strategy for improving multi-functional structural materials (MFSM) consisted in increasing complexity and reducing size of their microstructure. The METAFORES project is focusing on one class of MFSM, copper/niobium (Cu/Nb) high-strength and high-conductivity nanostructured metals which choice is motivated by their application in high field magnets. LNCMI and Pprime participants have shown how their deformation mechanisms are modified both by the reduction of microstructure size and the modification of the geometry. However, the exact origin of this observation is not clear and only advanced experimental tools coupled with simulation can help understanding the exact role of architecture (versus size effect) in the macroscopic mechanical response. Hence the project relies on three axes: 1) fine experimental microstructure characterization, 2) micromechanical modelling and 3) advanced strain distribution measurements. The first axis aims at providing accurate and statistically relevant data on grain geometry, texture and misorientation to ensure realistic representation of the microstructure in the finite element modeling computations and perform realistic and robust micromechanical and electrical modeling (PIMM and MINES participants). From this, correlations and scaling laws between stress, hardening and dislocation densities will be introduced in the crystal plasticity constitutive equations used in the second axis of the project. However these laws are not sufficient for describing the size-dependence of plastic strain fields: sophisticated continuum models are needed for full-field computations and comparison with strain field measurements. Therefore, computational homogenization methods recently developed at MINES will be implemented to compute the full-fields and the effective response of multiphase crystalline microstructures, including size-dependent crystal plasticity models: such novel approach will be applied to investigate microstructure and architecture effects. In parallel, a less time-consuming approach will be developed: mean-field homogenization methods such as the self-consistent scheme is especially well suited for polycrystals. But contrarily to a full-field approach, this scheme usually considers uniform stress inside grains; this drawback will be overcome by using the Ponte-Castaneda & Willis approach where microstructure features can be taken into account (grain shape and geometrical arrangement). This second original approach should allow obtaining additional insight into the effect of the alignment of Cu and Nb grains with the nanocomposites. The third axis deals with advanced experimental in-situ deformation experiments to monitor the non-uniform distribution of strain within the composites upon loading. Since diffraction offers a unique non-destructive tool for the measurement of internal strains into individual structural phases of the nanocomposites, in-situ loading strain measurements will be performed using a small tensile machine mounted on the 6T1 thermal neutrons diffractometer (LLB participant). In this way, strain pole figures will be obtained helping to characterize the mechanical responses of Nb and of the various scales of Cu and to compare the experimental strain distribution to the different simulations. Finally, all the experimental and simulation results will be combined to assess the roles of microstructure versus architecture in order to define design criteria for tailored MFSM not only from the choice of materials but also from their geometry (microstructure and shape).