L-PBF generatesspecific defects, namelylack of fusion (LoF), whichconstitute fatiguecrackinitiation sites.LoFbeingmostlylocatedin the volume of material,it is difficult toaccesstheir impact onthe fatigue crack growthrate (FCGR).This studyproposes to compareFCGR of internal crack with that of surface crack.To control the crack initiationsite, internal artificialdefects havebeen introduceddirectlybyL-PBFin test specimensmade ofIN718. Todeterminethe FCGR of internal crack,a methodologycoupling X-ray microtomography, direct current potentialdrop technique and finite element analysiswas developed.Surface crack FCGR was assessed by striation counting and optical measurement.The FCGR for internal cracks appears slower than for surface cracks.The influenceof the microstructure on fatigue crack growth mechanism was analyzed by EBSD and TEM.Given the large grain size, a strong influence of the microstructureon thecrack pathis observed. For internal initiation, the crack grows along the slip bands, resulting in a faceted fracture surface and changes of direction on grains boundaries. This means that grain boundaries act as obstacles, resulting in a slower FCGR for internal cracks.Thiscrack propagationmechanismappearssimilar towrought IN718 tested in vacuum/inert atmosphere. Theseresultsappear to berelated tothe atmosphere ofinternaldefects.In this case, the“inert”atmosphere inherited from L-PBF process promotesreversible slips in the crack tip plastic zone, andconsequentlythecrack grows on a limited number of slip planes.

This research aims to clarify the driving forces behind interfacial damage in thermal barrier coatings associated with buckling-driven delamination. Using an artificial interfacial defect processed by laser shock, thermomechanical fatigue loadings are investigated both with or without a through-thickness temperature gradient. In situ infrared imaging enables the tracking of further debonding, allowing assessment of the influence of complex loading conditions on the interfacial damage rate. Based on these findings, a clear ranking of the influence of thermomechanical fatigue parameters is established, including temperature, temperature gradient, cooling rate, strain level, and stress relaxation during dwell time at maximum temperature. A sensitivity analysis was carried out using a finite element method, considering temperature gradients and the realistic geometry of the blister. Through-thickness gradients were shown to increase the maximum stress intensity factors at the interface, driving monotonic damage of the interface. The interface temperature and the local strain amplitude govern the stress intensity factor amplitude and subsequent interfacial toughness decrease, driving fatigue damage of the interface.

The durability of thermal barrier coating (TBC) systems is strongly influenced by the interaction between oxidation of the metallic bond coat and its mechanical behavior. While the response of bond coats under isothermal monotonic loading has been widely studied, the effect of thermal cycling remains poorly understood, even though cyclic loading naturally arises from the mismatch in coefficients of thermal expansion between the ceramic top coat, thermally grown oxide, metallic bond coat, and the superalloy substrate. In this work, high-energy X-ray diffraction was used to investigate the strain and stress evolution in the β -(Ni, Pt)Al bond coat of a standard TBC deposited on a nickel-based single-crystal superalloy during thermal cycling. Before in situ cycling, some of the studied specimens were aged through long furnace cycles. Strains and stresses in the β phase were quantified in situ using the sin^2ψ method combined with micromechanical modeling. The results reveal that plastic deformation in β is strongly controlled by evolving interfacial effects and by the cyclic β⇌γ ' phase transformation during thermal cycling. These mechanisms govern the accumulation of plastic strain in β and may promote rumpling, spallation, and ultimately TBC degradation. This study provides new mechanistic insight into bond-coat plasticity under thermal cycling.

Nowdays electrode materials of lithium batteries are mainly constituted by inorganic compounds based on transition metals such as cobalt, nickel or manganese. Although their performances are satisfying, these materials present several important drawbacks. Indeed these compounds are expensive and present high environmental footprints because they are prepared due to energy-consuming techniques from rare mineral precursors. Moreover, some metals are toxic and often hard to recycle. Eventually their reactivity leads to safety issues in abusive conditions. N-type organic electroactive compounds such as quinone, polyimide or carboxylate salts offer a cost-effective and environmental friendly alternatives to conventional electrode materials for electrochemical storage. Interestingly these products can be prepared using (green) organic and polymer chemistry from low cost (bio-based) precursors. Moreover these compounds are easy to recycle or reuse at their end of life. But until now, their implementation in full prototypes is still challenging especially due to their high solubility in liquid electrolytes but also related to their low electronic conductivity and the lack of lithium source. In order to demonstrate the interest of organic battery technology, several approaches have been studied at CEA at material, electrode and cell levels and will be presented. First new n-type structures based on quinones have been identified and synthesized targeting organic materials for positive electrode with high voltage (>3V vs Li + /Li) and high specific capacity (>100mAh.g -1 ). In particular a lithiated air-stable Mg(Li 2 )-p-DHT (magnesium (2,5-dilithium-oxy)-terephthalate) compound has been developed and produced at pilot scale in collaboration with CNRS-IMN. Moreover some works about electrode formulations of carboxylate and quinone based materials lead to the preparation of viable electrodes with high active material loading (>1mAh.cm -2 ) and low carbon content (<10%wt) and several meters of double-sided electrodes have been coated on pre-industrial equipment. Finally several full Li-ion prototypes (multi-layer prismatic cell) have been assembled with Mg(Li 2 ) - p-DHT based electrode versus graphite and the electrochemical performances are very promising with high capacity retention at high C-rate (>70% at 2C) or after 50 cycles (>95% of initial capacity) and a proven energy density of 60Wh.kg -1 at cell level. Our last studies about the influence of the nature of electrolyte will also be presented.

The recrystallization behavior of an advanced Ti2AlNb alloy was investigated after high temperature compression and isothermal heat treatment. Compression experiments were performed in the single-phase (1 domain at 1010, 1065 and 1121 degrees C with strain rates of 0.01 and 1 s - 1 , and in the dual-phase (1+O and (1+alpha 2 domains at 900 and 970 degrees C, respectively, with strain rates of 0.1 and 0.5 s - 1 . Compression was followed by isothermal heat treatment at 1065 degrees C to obtain a fully recrystallized microstructure. During the heat treatment, the recrystallized grains formed after compression in the single-phase (1 domain revealed a partial and preferential orientation parallel to the initial compression direction, while no preferential orientation was observed after compression in the dual-phase (1+O and (1+alpha 2 domains and further heat treatment. Moreover, compression in the two-phase domains allowed to obtain smaller grain size in the fully recrystallized microstructure. Two distinct recrystallization kinetics were observed. The majority of samples exhibited fast kinetics, with fully recrystallized microstructures achieved after a short 630 s heat treatment at 1065 degrees C. However, compression at 1121 degrees C and 10 -2 s - 1 belonged to a second group with longer recrystallization time of 1 h, suggesting different recrystallization mechanisms.

A bidentate NHC-thiolate ligand based on the imidazo[1,5-a]pyridine scaffold and featuring an extended π-system is described. It is derived from a readily available zwitterionic precursor and the chemistry of the corresponding homoleptic Ni(II) complex is investigated.

As the operation temperature of aero-engine increases, the threat of molten deposits, usually caused by volcanic ash or sand ingestion has a major concern to the durability of these systems. In thermal barrier coatings, the ceramic topcoat (TC) layer made of partially stabilized zirconia is highly sensitive to such corrosive attack by means of infiltration, causing their premature failure. Infiltration causes either a decrease in toughness and adhesion or an increase in stiffness of the TC layer. As a local method to assess the interface strength of TBCs, the Laser Shock Adhesion Test (LASAT) is investigated for the first time to a columnar ceramic coating with and without infiltration by a CMAS deposit. LASAT clearly shows the location of the minimum toughness zone within TC layer, which is associated with the zone of infiltration, the infiltration depth limit or the TGO/topcoat interface. This is key to assessing the mechanical weakening from such corrosive attack.

The catalytic hydrogen-isotope exchange (HIE) of unactivated C(sp3)─H bonds remains a formidable challenge, relevant for the synthesis of high-purity high-value perdeuterated NMR solvents such as pentane or tetrahydrofuran. Existing methods primarily rely on precious metal-based catalysts (eg. Ir, Ru) under homogeneous conditions. In pursuit of more sustainable alternatives, we report the synthesis of the heterobimetallic complex [Ta(CH2tBu)2(μ-CHtBu)2CoCp*], 1, which is used for the preparation of a novel silica-supported tantalum-cobalt heterobimetallic catalyst through Surface OrganoMetallic Chemistry (SOMC). This Ta/Co material demonstrated exceptional catalytic efficiency in perdeuterating pentane under mild conditions (room temperature, < 1 bar D2, 1 mol% cat.), outperforming both the Ta monometallic and the noble-metal based Ta/Ir heterobimetallic analogues. Furthermore, we took profit of the complementary arene HIE and deuterogenation activities of the Ta/M (M = Ir, Co) catalysts to develop a tandem catalytic synthetic strategy for the efficient preparation of perdeuterated tetrahydrofuran from furan, achieving up to 94% total deuterium incorporation. This novel catalytic system offers several key advantages such as a) mild reaction conditions, b) atom-efficient use of D2 as the deuterium source, and c) simplified handling, allowing for the recovery of pure deuterated solvent via simple condensation, not hampered by the use of solvents nor additives.

l-Ascorbic acid is being commonly used as a green reducing agent for graphene oxide. However, re-oxidation of reduced Graphene Oxide (rGO) was established when using a moderate to high concentration of l-ascorbic acid and/or long reduction time. This unexpected finding gives important direction about conditions to privilege to limit such re-oxidation.

The microstructure evolution of a Pt-rich gamma-gamma' coating deposited on a third generation CMSX-4 Plus nickel-based superalloy was investigated during relatively short thermal cycles (from 300 degrees C to 1100 degrees C with a dwell time of 5 min at 1100 degrees C) using both ex situ and in situ characterization techniques. Ex situ analyses, including Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDS) and postmortem X-Ray Diffraction (XRD), demonstrated that Pt and Al interdiffusion induced by thermal cycling leads to significant microstructure changes in the coating. Lattice parameters of gamma and gamma' phases were revealed to correlate with Pt content. In a novel approach, in situ XRD using laboratory equipment was employed to monitor microstructural evolution during 250 thermal cycles. This unique in situ analysis highlighted the microstructural differences at low and high temperatures within each cycle. For the first time, it was observed that partial dissolution of gamma' precipitates occurs at high temperatures, altering the local chemical composition of both gamma and gamma' phases.

Most high-temperature components are subject to out-of-phase thermomechanical fatigue (OP-TMF), which induces crack growth at low temperatures. However, OP-TMF has been little studied in the context of short cracks. This study focuses on the experimental sensitivity of OP-TMF loading conditions playing on temperature range, gradient, and dwell time for thin sheet superalloy specimens. The material of interest is a Co-based superalloy, HA188. It is widely used in combustion chambers. The experimental analysis is based on full-field measurements for temperature, strain and damage by infrared thermography, digital image correlation and high resolution images from 300 to 900 degrees C. The main conclusion is that the temperature gradient, together with the temperature amplitude, largely determines the strain amplitude and subsequent fatigue crack growth rate (FCGR) of short cracks. In situ measurements of damage and crack closure were obtained using supervised machine learning based on images. This clarifies that crack closure is only partial and that the crack network growth rate is consistent with the individual short crack growth rate. Finally, 3D finite element analysis considering realistic temperature field and strain energy based FCGR model was able to evaluate the fatigue life in this context. It is shown that the OP-TMF FCGR is very close to the FCGR of the maximum temperature of the TMF cycle due to partial crack closure.

Salt metathesis between an alkali-stabilized tantalate complex, [Li(thf)2][Ta(CtBu)(CH2tBu)3] (1), and a series of alkylcyclopentadienyl 3d transition metal halide dimers, [Cp'M(μ-X)]2 (2-MX, Cp' = 1,2,4-tBu3C5H2, X = Cl, Br or I), provides a set of perhydrocarbyl-stabilized heterobimetallic complexes [Ta(CH2tBu)2(μ-CHtBu)2MCp']/[Ta(CH2tBu)3(μ-CtBu)MCp'] (3-M, M = Cr, Mn, Fe, Co, Ni). A combination of single-crystal X-ray diffraction, spectroscopic studies and computational investigations reveals that the species 3-M make up a series of nearly isostructural molecules, some of which exhibit unusual coordination geometries and an atypical α-hydrogen tautomerism. Most of these Ta-M pairs are rare or unprecedented in bimetallic molecular compounds and were designed as potential alternatives to analogous compounds in which tantalum is combined with more costly, heavy transition metals such as iridium or osmium, recently reported to be suitable precursors for Surface OrganoMetallic Chemistry (SOMC) and catalytic H/D exchange reactions.

Fischer-Tropsch conversion of syngas to hydrocarbons is proposed to begin with CO binding to the iron surface of the catalyst. CO adsorption on various iron facets of relevance to the Fischer-Tropsch process suggest that the Fe(111) surface is the most active for catalysis, and that CO bound to the penultimate layer of Fe atoms or the b-state is the resting state during catalysis. Notably, a μ-1,2 mode was discarded for the b-state due to a lack of exemplar molecular species and expectation that such a mode would have a higher energy infrared (IR) absorption than observed experimentally (viz. 1735-1860 cm-1). Here, we report the synthesis of a diiron(I/II) complex in which CO binds μ-1,2: (Fe(OTf))(Fe(THF)(μ-1,2-CO))L where L2- is a bis(β-diketiminate) cyclophane (1). Surprisingly, the observed νCO at 1763 cm-1 for 1 compares well with that reported for b-state. Electron paramagnetic resonance (EPR), Mössbauer, and density functional theory (DFT) results support a weakly coupled s = 3/2 iron(I) and s = 2 iron(II) pair. Reduction of 1 results in C-O cleavage and C-C bond formation to yield a ketenylidene (CCO) complex as a major product observed spectroscopically.

A multi-scale methodology is developed in conjunction with a probabilistic fatigue lifetime model for structures with pores whose exact distribution, i.e. geometries and locations, is unknown. The method takes into account uncertainty in fatigue lifetimes in structures due to defects at two scales: micro-scale heterogeneity meso-scale pores. An element-wise probabilistic strain-life model with its criterion modified for taking into account multiaxial loading is developed for taking into account the effect of micro-scale defects on the lifetime. Meso-scale pores in the structure are taken into account via statistical modelling of the expected pore populations via a finite element method, based on tomographic scans of a small region of porous material used to make the structure. A previously implemented Neuber-type plastic correction algorithm is used for fast full-field approximation of the strain-life criterion around the statistically generated pore fields. The probability of failure of a porous structure is obtained via a weakest link assumption at the level of its constituent finite elements. The fatigue model can be identified via a maximum likelihood estimate on experimental fatigue data of structures containing different types of pore populations. The proposed method is tested on an existing high-cycle fatigue data-set of an aluminium alloy with two levels of porosity. The model requires lesser data for identification than traditional models that consider porous media as a homogeneous material, as the same base material is considered for the two grades of porous material. Numerical studies on synthetically generated data show that the method is capable of taking into account the statistical size effect in fatigue, and demonstrate that fatigue properties of subsurface porous material are lower than that of core porous material, which makes homogenisation of the method non-trivial.

This paper introduces a new local plastic correction algorithm that is aimed at accelerating elasto-plastic finite element (FE) simulations for structural problems exhibiting localised plasticity (around e.g. notches, geometrical defects). The proposed method belongs to the category of generalised multi-axial Neuber-type methods, which process the results of an elastic prediction point-wise in order to calculate an approximation of the full elasto-plastic solution. The proposed algorithm relies on a rule of local proportionality, which, in the context of J2 plasticity, allows us to express the plastic correction problem in terms of the amplitude of the full mechanical tensors only. This lightweight correction problem can be solved for numerically using a fully implicit time integrator that shares similarities with the radial return algorithm. The numerical capabilities of the proposed algorithm are demonstrated for a notched structure and a specimen containing a distribution of spherical pores, subjected to monotonic and cyclic loading. As a second point of innovation, we show that the proposed local plastic correction algorithm can be further accelerated by employing a simple meta-modelling strategy, with virtually no added errors. At last, we develop and investigate the merits of a deep-learning-based corrective layer designed to reduce the approximation error of the plastic corrector. A convolutional architecture is used to analyse the neighbourhoods of material points and outputs a scalar correction to the point-wise Neuber-type predictions. This optional brick of the proposed plastic correction methodology relies on the availability of a set of full elasto-plastic finite element solutions to be used as a training data-set.

2D materials, such as transition metal dichalcogenides, are ideal platforms for spin‐to‐charge conversion (SCC) as they possess strong spin–orbit coupling (SOC), reduced dimensionality and crystal symmetries as well as tuneable band structure, compared to metallic structures. Moreover, SCC can be tuned with the number of layers, electric field, or strain. Here, SCC in epitaxially grown 2D PtSe 2 by THz spintronic emission is studied since its 1T crystal symmetry and strong SOC favor SCC. High quality of as‐grown PtSe 2 layers is demonstrated, followed by in situ ferromagnet deposition by sputtering that leaves the PtSe 2 unaffected, resulting in well‐defined clean interfaces as evidenced with extensive characterization. Through this atomic growth control and using THz spintronic emission, the unique thickness‐dependent electronic structure of PtSe 2 allows the control of SCC. Indeed, the transition from the inverse Rashba–Edelstein effect (IREE) in 1–3 monolayers (ML) to the inverse spin Hall effect (ISHE) in multilayers (>3 ML) of PtSe 2 enabling the extraction of the perpendicular spin diffusion length and relative strength of IREE and ISHE is demonstrated. This band structure flexibility makes PtSe 2 an ideal candidate to explore the underlying mechanisms and engineering of the SCC as well as for the development of tuneable THz spintronic emitters.

The brittleness of an aluminide diffusionDiffusion coating protecting a René 125 Ni-based polycrystalline superalloyPolycrystalline superalloy was investigated over a wide range of temperatures in its as-received and thermally aged form. Isothermal and thermal cycled aging were performed on the coated system at a maximum temperature of 1100 ^∘C . MicrostructureMicrostructure evolutions and damage initiation within the coatingCoating were characterized. Interrupted tensile tests and thermomechanical fatigueFatigue tests were conducted to document critical stress-strain conditions leading to the coatingCoating crackingCoating cracking and lifetime for the case of thermomechanical fatigue loading. Advanced digital image correlationDigital image correlations and acoustic emission techniques were used to detect coating crackingCoating cracking. Isothermal oxidationOxidation orCyclic oxidation cyclic oxidation led to improved strain-to-failure due to metallurgical evolutions and also longer fatigue life under thermomechanical fatigueFatigue conditions.

This study investigates failure mechanisms in a typical thermal barrier coating (TBC) system comprising an EB-PVD columnar top coat, an aluminide bond coat, and a Ni-based single crystal superalloy substrate, simulating gas turbine operating conditions using a burner rig. TBC degradation, initiated by interfacial defects from the LASAT method, was studied during thermal gradient cycling under fast and slow cooling. In-situ optical and infrared imaging, along with ex-situ SEM cross-sectional analysis, monitored failure mechanisms. The Laser Shock for Damage Monitoring (LASDAM) technique provided insights into gradient and cooling rate impacts on columnar TBC damage. Results showed significant effects of cooling rate on delamination and localized failure at blister sites, with LASDAM revealing significant overheating at damage sites. Analysis included full-field temperature and damage assessment, emphasizing blister-driven delamination under severe thermal gradients. Discussion focused on elastic stored energy effects, noting that fast cooling induced transient conditions where reversed temperature gradients increased damage, limiting TBC lifespan.

Zn-Al-Mg coatings are characterized by a complex microstructure with dendritic and eutectic phases. This heterogeneous phase distribution contributes to multiple deformation and damage mechanisms. The presence of brittle phases promotes crack initiation and propagation. This study reveals a new deformation and damage mechanism of a Zn-Al-Mg coating, where twinning can induce crack initiation in the eutectic region. The chronology of different events leading to crack initiation and propagation is clearly established by in-situ tensile testing in a scanning electron microscope, which helps to establish a detailed characterization of the mechanical behavior of the coating.