Yves Bréchet

• Hc at Atomic Energy and Alternative Energies Commission

Growing evidence in the literature highlights the presence of bainitic ferrite with partial carbon supersaturation at low temperatures. Diffusional growth models correctly predict the lengthening rate of plate-like ferrite but often underestimate carbon content due to the assumption of carbon local equilibrium at the interface, valid at elevated te...

The lengthening of bainitic ferrite laths in a model alloy containing a carbon gradient was observed in-situ using a Laser Scanning Confocal Microscope (LSCM). Results show that the observed lengthening rates increase with increasing temperature and decreasing carbon content. Crystallographic analysis was conducted by ex-situ electron backscattered...

Recently, in-situ TEM straining experiments on pure copper have unraveled a high stress irradiation creep mechanism. Irradiation induced unpinning of dislocations from defects has been observed and the mean pinning lifetime has been determined. In the present study, molecular dynamics simulations are performed on pure copper to investigate the impa...

In-situ TEM straining experiments were performed on pure copper to investigate the dislocation activity under heavy ion irradiation and high applied stress levels. The unpinning of dislocations from irradiation defects followed by glide was observed under irradiation at stress levels just below the critical stress for dislocation glide without irra...

Room temperature cyclic deformation of solution treated AA6061 led to the development of a high number density of Mg/Si clusters. The fine dispersion of clusters resulted in a strength comparable to that obtained using the T6 condition. Subsequent heat-treatment has the potential to further increase the strength of the alloy. Slow heating from room...

Metastable austenite strongly influences the mechanical properties of many advanced high strength steels (AHSS) and its formation kinetics during intercritical annealing strongly depend on the initial microstructure. In this contribution, we have performed detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range o...

Zirconium alloys used in nuclear reactors undergo irradiation creep, which consists of a visco-plastic deformation activated by irradiation occurring under constant load. However, the fundamental underlying mechanisms have not been unraveled yet. A new high-stress irradiation creep mechanism for recrystallized Zircaloy-4 has recently been proposed...

Grain growth in high-manganese steel (HMS) was studied at high temperatures (1273 K to 1473 K). Grain growth was found to be two orders of magnitude slower than that in a commercial low-Mn steel, as indexed by average experimentally determined mobilities. Electron backscatter diffraction maps of grain boundaries revealed the presence of numerous sp...

Design of architectured materials and structures, whether in nature or in engineering, often relies on forms of optimization. In nature, controlling architecture or spatial heterogeneity is usually adaptive and incremental. Naturally occuring architectured materials exploit heterogeneity with typically graded interfaces, smoothly transitioning acro...

This book deals with a group of architectured materials. These are hybrid materials in which the constituents (even strongly dissimilar ones) are combined in a given topology and geometry to provide otherwise conflicting properties. The hybridization presented in the book occurs at various levels - from the molecular to the macroscopic (say, sub-ce...

Matlab code to calculate tunnel electrical resistance.

Abstract Thin amorphous alumina layers (10 to 40nm thick) are processed on sputtered aluminum thin film (500nm) by atomic layer deposition (ALD) at low temperature (85° C). Global methodology combining quantitative experimental observations of fracture and numerical modeling is proposed to obtain the fracture strength of ALD thin film on Al layer....

The past few years have seen a considerable amount of research devoted to nanostructured transparent conducting materials (TCM), which play a pivotal role in many modern devices such as solar cells, flexible light-emitting devices, touch screens, electromagnetic devices, and flexible transparent thin film heaters. Currently, the most commonly used...

The creep behavior under heavy ion irradiation of 200 nm and 500 nm thick annealed Cu films is characterized using on chip uniaxial microtensile test structures. The tests are performed at room temperature with an applied stress between 100 and 250 MPa and a damage rate of 5 × 10⁻⁴ and 6.3 × 10⁻⁴ dpa s⁻¹. The deformation rates produced under irradi...

Silver nanowire (AgNW) networks are emerging as one of the most promising alternatives to indium tin oxide (ITO) for transparent electrodes in flexible electronic devices. They can be used in a variety of optoelectronic applications such as solar cells, touch panels and organic light-emitting diodes. Recently they have also proven to be very effici...

Advancement in the science and technology of random metallic nanowire (MNW) networks is crucial for their appropriate integration in many applications, including transparent electrodes for optoelectronics and transparent film heaters. We have recently highlighted the discontinuous activation of efficient percolating pathways (EPPs) for networks hav...

.xls file with multilayer elastic models to analyze indentation of 2, 3 or more layers on a substrate.

The austenitization from a spheroidized microstructure during intercritical annealing was studied in a Fe-0.1C-3.5Mn alloy. The austenite grains preferentially nucleate and grow from intergranular cementite. The nucleation at intragranular cementite is significantly retarded or even suppressed. The DICTRA software, assuming local equilibrium condit...

The complex microstructures developed during post-welding heat-treatment in the vicinity of the fusion line between a ferritic and austenitic steel were examined in the case of submerged arc welded 18MND5/309L dissimilar joints. Quantitative measurements of the carbon distribution in the as-welded and post-weld heat-treated conditions were performe...

Finite amount of fossil fuel, global warming, increasing demand of energies in emerging countries tend to promote new sources of energies to meet the needs of the coming centuries. Despite their attractiveness, renewable energies will not be sufficient both because of intermittency but also because of the pressure they would put on conventional mat...

La contribution de Jacques Friedel à la théorie de la plasticité des métaux et alliages est mise en perspective avec son héritage. Les évolutions de la discipline vers la « métallurgie numérique » sont discutées, en les plaçant sous un éclairage « friedélien ».

An on chip test method has been developed to characterize the irradiation creep behavior of thin freestanding films under uniaxial tension. The method is based on the use of a long beam involving large internal stress protected from the irradiation flux that imposes a spring like deformation to a specimen beam. These elementary freestanding structu...

Radiation induced segregation in ferritic FeeCr alloys is studied by Atomistic Kinetic Monte Carlo simulations that include diffusion of chemical species by vacancy and interstitial migration, recombination, and elimination at sinks. The parameters of the diffusion model are fitted to DFT calculations. Transport coefficients that control the coupli...

Silver nanowire (AgNW) networks are efficient as flexible transparent electrodes, and are cheaper to fabricate than ITO (Indium Tin Oxide). Hence they are a serious competitor as an alternative to ITO in many applications such as solar cells, OLEDs, transparent heaters. Electrical and optical properties of AgNW networks deposited on glass are inves...

In October 2013, a two-day symposium was held to conclude the year 2012 / 2013 of the Liliane Bettencourt Chair of Technological Innovation which had been devoted “customized materials”. Steel wool The theme chosen for this symposium was “Filling Gaps in Materials Space: Methods and applications”. Developing “customized materials”, which is proving...

Nanostructured ferritic steels were mechanically alloyed with various contents of oxide-forming yttrium and titanium (0, 0.05, 0.3 and 1 wt%). The microstructure evolution of the milled powders during non-isothermal annealing treatments was studied using in situ synchrotron X-ray diffraction. Recrystallization and grain growth were quantified upon...

Transparent electrodes (TE) constitute a key component of optoelectronic devices such as solar cells, efficient organic light-emitting diodes (OLEDs), touch screens. Currently the most widely used TE is indium tin oxide (ITO), which offers low resistivity and high transparency in the visible. However the scarcity of indium and the lack of flexibili...

Solid state phase transformations in metals, and more precisely the science of transformation interfaces, is a key point to understand the formation of nano/microstructure, and thus, as a result, many physical properties such as mechanical properties, conductivity, thermoelectric and magnetic properties of materials.

Several phase transformations occur during post-weld heat-treatment in the vicinity of the fusion line between a low-alloy steel and an austenitic stainless steel, driven by large gradients of carbon chemical potential across adjacent regions (bainite / martensite / austenite). Cementite dissolution in the low-alloy side provides carbon which diffu...

A geometric method is presented to design cellular structures that actuate upon inflation. Through finite element simulations, it is demonstrated that these structures can undergo large directed expansions upon inflation and efficiently convert an input pressure into an output force. This design concept is validated through the controlled swelling...

An in situ X-ray diffraction experiment was set up to study the microstructural evolution of a nanostructured oxide dispersion-strengthened ferritic steel produced by high-energy ball milling. Dislocation density and grain growth between 20 and 1100 °C were quantified by coupling-modified Williamson–Hall and Warren–Averbach methods. During the earl...

The plastic and fracture behavior of ultrafine-grained dual-phase (UFG-DP) steels (Fe-0.1 wt%C-3.5 wt%Mn) were analysed from the comparison with the coarser grained DP microstructures taken as references. The UFG-DP steel exhibits a superior balance between strength, uniform elongation and true fracture strain. The higher mechanical performance is...

A simple model describing the hydrophilic adhesion between solid surfaces, with low roughness is proposed to explain both the influence of the interface roughness and quantity of water present at the interface on the work of adhesion and work of separation. The observed hysteresis between adhesion and separation is explained by the evolving distrib...

A molecular-dynamics type simulation method, which is suitable for investigating the dewetting dynamics of thin and viscous liquid layers, is discussed. The efficiency of the method is exemplified by studying a two-parameter depinning-like model defined on inhomogeneous solid surfaces. The morphology and the statistical properties of the contact li...

A model for interphase precipitation has been developed based on the ledge mechanism of austenite-to-ferrite transformation. Carbide precipitation is considered on the migrating ferrite/austenite interface as an interaction of transformation and precipitation kinetics. The derived equations describe sheet spacing and particle spacing of interphase-...

We briefly recall the important career, together with the moving personality, of the great fundamental metallurgist and solid state physicist Jacques Friedel who passed away on the 27th of August 2014 in Paris.

A level set method is used as a framework to study the effects of including material interface properties in the optimization of multi-phase elastic and thermoelastic structures. In contrast to previous approaches, the material properties do not have a discontinuous change across the interface that is often represented by a sharp geometric boundary...

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing. Understanding the behavior of such films is crucial for the optimization of transparent conductive electrodes which find many applications. An in-...

It is well known that solid state precipitation forms an important microstructural component of many engineering alloys and is used to help control the bulk mechanical properties. In this contribution, a thermal treatment process is introduced that can induce solid state precipitation also on the surfaces of engineering alloys resulting in patterne...

The seed capsule of Delosperma nakurense is a remarkable example of a natural hygromorph, which unfolds its protecting valves upon wetting to expose its seeds. The beautiful mechanism responsible for this motion is generated by a specialized organ based on an anisotropic cellular tissue filled with a highly swelling material. Inspired by this syste...

The influence of the dynamics of the direct wafer bonding process on the curvature of the final wafer stack is investigated. An analytical model for the final curvature of the bonded wafers is developed, as a function of the different load components acting during the bonding front propagation, using thin plate theory and considering a strain disco...

Magnetism plays a crucial role in the thermodynamic and kinetic properties of ferritic alloys. In fact, magnetism increases the solubility limit of Cr in Fe, inducing an asymmetrical phase diagram. Moreover, the phase transition from ferromagnetic to paramagnetic (F/P) iron alloys modifies to a large extent the system response to different environm...

Nous examinons le rôle des différences physiques, chimiques et physicochimiques entre les conséquences des accidents de centrales électronucléaires – désignées EN dans la suite – et les accidents majeurs des grands équipements technologiques à hauts risques (extraction, raffinerie et transport du pétrole, grande chimie, lancer de navette spatiale,...

With the growing interest in flexible electronics and the increased utilization of Indium Tin Oxide electrodes for display and photovoltaic applications the need for new materials is emerging. In this work we present the electro-optical properties of Ag nanowire networks as an alternative transparent conductive material. A comparison of different f...

The use of a soft material, such as foam, as core in a sandwich panel offers increased acoustical transmission loss at the expense of a decrease of flexural stiffness. A genetic algorithm is used to explore the possible trade-off between mechanical and acoustical properties of foam core sandwich panels in a minimum weight design.

This paper describes a proposal for a multi-material design procedure. First, the context of the study and the requirements of the multi-material must be clearly defined in order to specify the parameters that the designer must select or optimise in order to produce the design: the components and their volume fraction, the architecture and morpholo...

Recrystallization of a ball-milled ferritic ODS steel is studied towards its evolution from as-milled powder to consolidated state. This characterization has been made possible by using a combination of X-ray Diffraction (XRD) and an innovative method based on an Automated Crystallographic Orientation Mapping (ACOM) tool attached to a Transmission...

The evolution of characteristic features of interphase precipitation in steels with progressive of austenite-to-ferrite transformation is analyzed from both experimental and modeling approaches. The model developed describing the time and temperature evolution of sheet spacing and particle spacing shows good agreement with the experimental data. Th...

Ball-milled powder materials exhibit complex microstructure due to the high amount of energy introduced by the process which therefore leads to very fine far-from-equilibrium structures. This elaboration method is used to produce Oxide Dispersion Strengthened ferritic steels that are developed for high temperature applications.To study the complex...

The concept of novel responsive materials with a displacement conversion capability was further developed through the design of new machine-augmented composites (MACs). Embedded converter machines and MACs with improved geometry were designed and fabricated by multi-material 3D printing. This technique proved to be very effective in fabricating the...

Thermal annealing is shown to be a successful approach to reduce the electrical resistance of transparent electrodes made of randomly oriented silver nanowires (AgNWs). A decrease in the electrical resistance by several orders of magnitude, whilst maintaining optical transmission (above 85%), is demonstrated. Several mechanisms involved in the elec...

The use of random metallic nanowire networks as transparent conductive materials (TCMs) is increasing rapidly. These materials can be used in flexible/stretchable electronics, flexible displays, touch screens, photovoltaics or as transparent heaters. Metallic nanowire networks can be deposited by using low-cost and scalable deposition technique...

Research is increasingly being dedicated towards replacing rare earth elements in Transparent Conductive Materials (TCMs). In this work we present the investigation of silver nanowire (AgNW) networks as transparent electrodes for solar cell applications. Metallic nanowire networks can be deposited via low cost deposition techniques and exhibit...

Research is increasingly being dedicated towards finding emerging materials aiming at playing a prominent role in energy issues. Transparent electrodes are a key component of devices such as solar cells or efficient lighting (such as OLED). Among emerging transparent conductive materials, metallic nanowire networks appear to be a very promising...

Silver nanowire (AgNW) networks have recently been the focus of intense research due to their potential use as transparent electrodes in solar cells, flat panel displays or transparent heaters. Metallic nanowire networks can be deposited using low-cost and scalable deposition techniques on flexible substrates. For improving the transport proper...

Several microstructural parameters of the NR6 nickel-based superalloy were varied by applying four heat treatment procedures. Tensile creep tests were performed in air at 700 degrees C and 700 MPa on specimens exhibiting different grain sizes, strengthening gamma' precipitate sizes and distributions and grain boundary morphologies. Flat creep speci...

A new criterion for nucleation in the case of dynamic recrystallization is proposed in order to include the contribution of the grain boundary energy stored in the microstructure in the energy balance. Due to the nucleation events, the total surface area of pre-existing grain boundaries decreases, leading to a nucleus size smaller than expected by...

The auto locking structures are a new category of hybrid materials. They consist of periodic pavings of elementary blocks. The geometry of the blocks, the friction between the blocks as well as the boundary conditions applied to the edge of the assembly play a central role in the cohesion of the assembly. The effect of the boundary conditions has b...

The goal of this study is to understand the complex microstructures which form at the interface between a low-alloy steel and a stainless steel during welding and subsequent heat-treatment at 610°C. A dual approach with both experimental measurements and thermodynamic and kinetic modeling has been chosen for both solidification and solid-state phas...

Properties of entangled materials, made of fibers, depend on the number and the nature of contacts between fibers and fibers orientation. Nonsintered and sintered steel wools have been characterized by x-ray tomography to extract structural information such as fibers orientation and number of contacts before and during compression. Image analysis t...

Introduction Materials Experimental procedure Results Discussion Conclusion

Silver nanowire (AgNW) networks have recently been the focus of intense research due to their potential use as transparent electrodes in solar cells, flat panel displays or transparent heaters. Metallic nanowire networks can be deposited using low-cost and scalable deposition techniques on flexible substrates. For improving the transport proper...

During direct bonding, a thin gas film is trapped in-between the two wafers, leading to an interactive fluid/structure dynamics. A model of bonding dynamics is formulated using the plate approximation, Reynolds equation, and adhesion forces as the boundary condition at the bonding front. The transient equation is solved numerically in a one dimensi...

Zirconium alloys are typically used in nuclear pressurized water reactors (PWR) as fuel cladding tubes due to their chemical stability and their mechanical strength at operating temperatures (≈300 °C). However, the corrosion of Zr-based cladding tubes is one of the factors limiting the burn-off rate in PWRs. It is commonly accepted that the corrosi...

Duplex stainless steels (DSS) involve two ductile phases, i.e. ferrite and austenite, with a proportion of each phase around 50%. The main advantage in comparison with other austenitic and ferritic stainless steels is the excellent combination of high strength and corrosion resistance together with good formability and weldability. Unfortunately, D...

Usually niobium is added in ferritic stainless steels to avoid chromium carbides precipitation and then to improve corrosion resistance and to avoid embrittlemet. This study shows that a low Nb stabilization makes recrystallization nucleation much faster and prevents incomplete recrystallization. A qualitative interpretation, based on interaction w...

Atomic scale observations of the oxide formed on stainless steels, under simulated nuclear reactor conditions, are performed to estimate the oxide layer contribution on stress corrosion cracking (SCC) mechanisms. A duplex oxide composed of a chromium enriched inner layer (Fe1.5Cr1.5O4) and an outer layer composed of magnetite crystallites (Fe3O4) i...

Direct metal bonding represents an advanced joining technology that allows vertical stacking with electrical conduction and even heat dissipation. For most metals used as bonding layers, direct bonding when operating under ambient conditions involves metal oxides. The bonding interface saddles with a trapped oxide layer that might affect electrical...

Interactions between proteins and material or cellular surfaces are able to trigger protein aggregation in vitro and in vivo. The human insulin peptide segment LVEALYL is able to accelerate insulin aggregation in the presence of hydrophobic surfaces. We show that this peptide needs to be previously adsorbed on a hydrophobic surface to induce insuli...