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Micropillar compression is a method of choice to understand mechanics at small scale. It is mainly studied with electron microscopy or white-beam micro-Laue X-ray diffraction. The aim of the present article is to show the possibilities of the use of diffraction with a coherent X-ray beam. InSb micropillars in epitaxy with their pedestals (i.e. their support) are studied in situ during compression. Firstly, an experiment using a collimated beam matching the pillar size allows determination of when the sample enters the plastic regime, independently of small defects induced by experimental artefacts. A second experiment deals with scanning X-ray diffraction maps with a nano-focused beam; despite the coherence of the beam, the contributions from the pedestal and from the micropillar in the diffraction patterns can be separated, making possible a spatially resolved study of the plastic strain fields. A quantitative measurement of the elastic strain field is nevertheless hampered by the fact that the pillar diffracts at the same angles as the pedestal. Finally, no image reconstructions were possible in these experiments, either in situ due to a blurring of the fringes during loading or post-mortem because the defect density after yielding was too high. However, it is shown how to determine the elastic bending of the pillar in the elastic regime. Bending angles of around 0.3° are found, and a method to estimate the sample's radius of curvature is suggested.

International audience; In this work, the effect of the loading path on the multicracking of Nickel thin films on Kapton® substrate was studied thanks to an experimental set-up combining controlled biaxial deformation, x-ray diffraction and digital image correlation. Samples were biaxially stretched up to 10% strain following either a single equibiaxial path or a complex one consisting of loading successively along each of the axes of the cruciform specimen. While the first path leads to a mud-crack pattern (random), the second leads to a roman-bricks one (square). Moreover, the in situ x-ray diffraction experiments show that the stress field developed in the thin film during the multicracking is clearly dependent on the loading path. By combining the study of stresses and x-ray diffraction peaks linewidth, we evidenced mechanical domains related to initiation of cracks and their multiplication for each loading path. Moreover, stress evolution in the thin film during mud-crack pattern formation is significantly smoother than in the case of roman-bricks one as represented in the plane stress space.

Measurements in a van der Pauw configuration often require the use of complicated mathematical expressions or implicit relations, which may be computer-time-consuming or tedious to implement in a given software. Thus, a closed-form expression is often desirable. We propose to approximate these relations by closed-form analytical functions using only basic operators that can be easily implemented. We present explicitly the functions and the numerical values of their parameters for the cases of standard van der Pauw measurement, anisotropic resistivities, and the probe position correction factor. The discrepancy with the exact values is smaller than 10−5, which is sufficient for practical purposes.

This work takes place in the general context of a better understanding of materials degradation mechanisms in extreme environments. In particular, the aim of the present study was to correlate microstructural elements to growth stress magnitude evolution and stress release mechanisms for thermally grown chromia thin films on NiCr alloys. Strains in thermally grown oxides have been measured in-situ, as the oxides develop and evolve. Data have been acquired from oxides grown for different high temperatures evolutions on NiCr model alloys that form Cr2O3. Using synchrotron X-Ray at the ESRF (Beamline BM02) coupled with an induction furnace, Debye-Scherrer diffraction patterns from the oxidizing specimen were recorded in air at temperature between 700-1000°C and during cooling. The distortion of the diffraction rings was analyzed to yield the in-plane strain. Thermal stresses imposed on Cr2O3/NiCr by abruptly reducing the sample temperature for a period of time, exploiting the thermal expansion difference between oxide and substrate, showed noticeable subsequent stress relaxation by creep. Such a mechanism was monitored using time-dependent in situ measurements of strain relaxation in the oxide. The main results obtained from these experiments are the kinetic of the growth stress from the isothermal measurements (isothermal plateau), and the study of the stress release mechanism after the low-temperature jumps. In complement, the oxide microstructure development during the course of oxidation is also investigated from both the peaks intensity and width evolution. In all cases, the steady stage growth strain was relatively low and compressive. Different degrees of relaxation were also found on cooling depending on scale microstructure through the variation of the initial oxidation conditions. Results are compared with other reports of residual stresses evolution in Cr2O3 scales.

A novel experimental approach to study the cyclic plastic deformation of thin metallic films is presented. 300 nm thick Ni films are deposited on both sides of a pre-tensile soft substrate which allows to deform the films alternately in tension and compression (approximately from +2.7 GPa down to −2 GPa) relative to the as-deposited residual stress state. Nanocrystalline thin films' intrinsic elastic strains (or stresses) and true strains have been measured step by step during two loading/unloading cycles thanks to the X-ray diffraction (XRD) and digital image correlation (DIC) techniques respectively. From the first cyclic deformation, a significant Bauschinger effect is evidenced in the films, however, little or no cyclic hardening is observed during the two cyclic tests.

International audience; An experimental method for a single layer is extended to determine the elastic properties of nanostructured W/Cu multilayers on a flexible substrate. The strain difference between the W/Cu-polyimide-W/Cu composite and the uncoated substrate, measured by dual digital image correlation, allows us to extract the effective Young’s modulus of W/Cu multilayers (20 periods) equaling 216±13 GPa. Finite element method is then performed, which agrees well with the experiment and classical rule of mixture (ROM) theory demonstrating that the extension to multilayers is effective and reliable. The numerical analysis also interestingly shows that the strain difference is linearly related to the thickness ratio (W/Cu), periods and sublayer thickness, respectively. In contrast to ROM theory, this approach could potentially be used for the evaluation of properties and design of emerging/unknown functional multilayers, whether or not they are crystalline or amorphous.

In this paper, in situ measurements of synchrotron x-ray pole figure have been performed during incremental uniaxial deformation test on a single-crystal gold foil. The 50 nm thick Au thin film was elaborated by ion sputtering at 400 °C on NaCl single crystal as a template. The resulting film consists of a single-crystal gold foil containing a small density of thin and small {111} growth twins (few nm thick and few tens of nm long) revealed by x-ray pole figure measurement. The as-deposited gold single crystal was then transferred onto flexible polyimide substrates for deformation test. This work focuses on the relative evolution of the diffracting volume related to growth twins during a loading-unloading tensile test. Macroscopic applied deformations and x-ray pole figures were measured in situ during a uniaxial tensile test in the Au [110] direction. X-ray pole figures clearly evidenced the relative evolution of the diffracting volumes related to the (111) and 1 ¯ 1 ¯ 1 twins which exhibit a huge increase of about 450% at a uniaxial applied true strain of about 4%. The concomitant variation of diffracting volumes related to the two other twin variants (namely 1 ¯ 11 and 1 1 ¯ 1 twins) shows a relatively low decrease of 25%. The results open out onto a true strain-twinning volume hysteresis curve, indicative of the deformation mechanisms of gold thin films that can be interpreted as a twinning-detwinning mechanism.

International audience; The dependence on thermal history of the plasticity mechanisms occurring in nanocrystalline gold thin films is evidenced thanks to relaxation tests combined with in-situ synchrotron X-ray diffraction. The two techniques complement one another. The activation parameters show that the films deform mainly by dislocations and give indications about their mean free paths, whereas the Bragg peak positions, widths and areas bring invaluable information on residual stress as well as on some plasticity properties, like dislocation storage inside the grains or grain rotations. For the demonstration, two sputter-deposited nanocrystalline 50 nm-thin films deposited onto stretchable substrates are studied. It is shown that an as-grown sample (at a homologous temperature of 0.22) presents a stress-assisted annealing, thus decreasing its initial defect density, whereas if a thermal annealing (3 h at [Math Processing Error], corresponding to a homologous temperature of 0.35) has been applied to the sample before the tensile test, it deforms by conventional plasticity, and the dislocations are not stored inside the grains. These mechanisms lead to different work-hardening properties. This work shows how a moderate annealing can have a profound influence on the mechanical behaviour of these thin films.

In this paper, a method is proposed to determine the in-plane elastic modulus of thin films. Thanks to our custom-designed dual digital image correlation (DIC) system, it is possible to measure the time-resolved strain of film and substrate simultaneously during the microtensile testing. The macroscopic strain difference between coated and uncoated section allows extracting the elastic constants of thin films with high precision. In the case of 400 nm tungsten films coated on each side of one substrate over half of the gauge length, the value obtained agrees well with the bulk one. Furthermore, finite element method (FEM) has been performed to simulate the mechanical behavior of the specimen. High consistency with theoretical and experimental results is verified.

Thin film technology is pervasive in microelectronics, and in optical, magnetic or micro-mechanical devices. The mechanical performance of such nanoscale structure is crucial for applications since it is related to device lifetime. Furthermore, the mechanical behavior of nanostructured materials is still not well known. In this work, nanostructured gold thin films with different thicknesses have been elaborated by sequenced ion beam sputtering to study size effect. The grain size is controlled by stopping the grain growth during the thin film growth. Using the biaxial tensile setup developed at the DiffAbs beamline of the French synchrotron facility SOLEIL, x-ray diffraction (XRD) measurements have been performed during controlled biaxial deformation tests on gold thin films deposited on Kapton substrate. Strain analysis of the gold thin films with different grain size and architecture has been achieved for a non equi biaxial loading with a force ratio of 0.8. XRD allows measuring the intra-granular strains using the so-called sin2ψ method while the macroscopic in-plane strains are measured simultaneously thanks to Digital Image Correlation. By analyzing the mechanical response of the different films, we conclude that gold thin films follow a plastic deformation mode whatever the grain size or thin film architecture.

Thin film architectures with brittle and ductile material layers are often combined for functionality. Easy to fracture brittle films are often necessary due to their function as diffusion barriers, adhesion or protective layers. Especially in the field of flexible and wearable electronics brittle materials may cause short lifetimes. Direct current magnetron sputtered bilayers on a polyimide substrate containing brittle Mo and ductile Al layers (Al/Mo/PI and Mo/Al/PI) as well as Al films (Al/PI) were subjected to equi-biaxial loading with in-situ X-ray diffraction measurements. The setup enabled the extraction of the stress and full width at half-maximum as a function of the strain. The data yields deeper insights into underlying deformation and fracture mechanisms and the significance of the layer arrangement. It will be demonstrated that for stretchable applications the position of the Mo layer affects the fracture strain of the bilayers and the individual layers.

International audience; Chromium-based alloys have been developed to form chromia layers in oxidizing environments for high temperature applications, providing a good protection against further oxidation. The mechanical behavior and oxide layer growth of yttria-coated or zirconium-doped Ni28Cr alloy are presently studied under high temperature oxidation conditions. These kind of reactive elements can decrease oxidation kinetics and significantly increase the adhesion of chromia layer on the metallic substrate. However, during oxidation, a compressive stress generally occurs in thermally grown oxide (TGO) due to the oxide layer and its mechanical interaction with the metallic substrate. These growth stresses, combined with the thermal stresses that develop during temperature changes, may initiate and cause layer cracking or spallation, which limits the lifetime of alloys in such a challenging environment. For prediction of this lifetime, it is important to know with accuracy the thermomechanical behavior of such a system. Therefore, a thermomechanical modelling is proposed and applied to optimize numerically the unknown parameters, especially viscoplastic ones. For the raw material and modified materials by reactive elements, the creep parameter decreases with a lower temperature, which means that the viscoplastic strain decreases with a decreasing temperature. For the yttria-coated or zirconium-doped material, the main result is an increase of the activation energy of this creep parameter with the quantity of reactive element.

In order to clarify the mechanical features of a metal under thermal cyclic loading for the system Ni30Cr- Cr 2 O 3 , a specific study has been carried out. In the present work, the residual stresses in both the metal and the oxide layer have been investigated. An adapted method is applied to process the experimental results that were obtained by using in-situ high temperature synchrotron diffraction at European Synchrotron Radiation Facility. The sin 2 ψ analysis provides information about the stress in metal and oxide. X-ray diffraction provides also the lattice parameter between crystallographic planes in the metal. To obtain correct stress values, a correction method is also proposed taking into account different discrepancies sources to ensure the equation of mechanical balance.

International audience; The viscoplastic behaviour of the model yttria-coated Ni28Cr alloy was studied under high temperature oxidation conditions for various small quantities of reactive element (RE). The main purpose was to determine the way the RE acts on the non-destructive stress relaxation mechanisms (creep) occurring in thermally grown chromia scales. After building of an initial chromia microstructure by 3 h oxidizing at 1273 K, temperature jumps were applied to generate thermal stress loading, the chromia scale microstructure being considered as stable. The generated stress was then released along 3 h isothermal periods and X-ray Synchrotron diffraction was used to follow in situ its evolution. The experimental curves were then simulated in order to calculate the creep coefficients, to evaluate the activation energy of the diffusion-creep mechanism and determine the diffusion coefficients and the elementary mechanisms associated to the viscoplastic behaviour of chromia scales in relation with the introduced RE quantity.

Indium Antimonide (InSb) single-crystalline micro-pillars were mechanically deformed by uniaxial compression loading-unloading cycles up to the beginning of the plastic regime. After deformation, 2D spatially resolved maps were collected via two X-Ray Diffraction (XRD) techniques: polychromatic micro-Laue and monochromatic micro-diffraction. In both techniques, the integrated diffracted intensity shows strong variations inside the pillar. Moreover, the shift and streaking of one spot in polychromatic XRD as well as the lattice strain and tilt components derived from monochromatic XRD reveal that the plastically deformed area is localized on the top of the pillar, in agreement with scanning electron microscopy images. The two XRD techniques are thus providing correlated but yet complementary information.

This work takes place in the general context of a better understanding of materials degradation mechanisms in severe environments. More particularly, its purpose is to correlate microstructural elements to growth stress magnitude evolution and stress release mechanisms for chromia thin films thermally grown on model NiCr alloys. X-ray elastic strains have then been measured in situ, as the chromium oxides develop and evolve, by using synchrotron X-ray diffraction, coupled with an induction furnace. 2D diffraction patterns were continuously recorded by applying different temperature variation procedures between 1000°C and 700 °C. Thermal stresses imposed on Cr2O3/NiCr system by abruptly reducing the sample temperature, i.e. by exploiting the thermal expansion difference between oxide and substrate, showed noticeable subsequent stress relaxation by creep. The main results obtained from these experiments were the kinetic of the growth stress from the isothermal measurements, and the study of the stress release mechanism after the temperature jumps to lower values. In complement, the oxide microstructure development during the course of oxidation was also investigated from both the peaks intensity and peaks width evolution. The creep coefficients could be estimated for the first time for chromia under the thin film form. It was proposed that the stress release by diffusion creep in the chromia films is very likely governed by a mechanism involving diffusion of oxygen ions at the chromia grain boundaries.

In this paper, a method to study cyclic deformations is used in a polycrystalline Ni thin film 600 nm thick with a W cap-layer of 20 nm. The Ni/W bilayer film was deposited onto compliant polyimide substrate allowing the film to be subjected to a relatively large tensile applied stress range during loading-unloading of the film/substrate composite. Film deformations were in situ measured both by synchrotron X-ray diffraction and digital image correlation during continuous cyclic uniaxial tensile test. This work focuses on the characterization of the deformation mechanisms during the first cycles of loading-unloading tensile test. It is found that up to a strain of 0.5% corresponding to an applied stress of 1.1 GPa the elastic strain of the Ni film follows precisely the strain applied to the substrate, but for larger applied stress the elastic strain of the metallic film, though completely reversible, is smaller than the substrate true strain. The results open out onto characteristic strain-strain hysteresis curves, indicative of the very first step of fatigue processes in the Ni/W thin film.

International audience; In the present work, mechanical features in thermal oxide films growing on metals have been investigated during cyclic thermal loadings. An adapted model is considered to describe the stress evolution within oxide films, taking into account thermomechanical couplings. These numerical predictions are compared with experimental results obtained using synchrotron diffraction at ESRF. In order to obtain the features of the system, an innovative data treatment is thus proposed and performed. By dealing with the frequency analysis of the system, the method is able to identify some mechanisms. This mechanical spectroscopy allows thus to confirm the thermomechanical description of a chromia-former alloy.

Metallic thin films deposited onto polymeric substrates find important technological applications as stretchable microelectronic devices. Academic research on these systems has mainly focused on uniaxial tensile tests, though biaxial stress states are generally applied during service. We study in this article the strain ratio effect on nanocrystalline 50 nm-thick gold thin films supported on a polyimide: equibiaxial applied strain vs uniaxial applied strain. The mechanical behaviors are compared with digital image correlation, x-ray diffraction, and relaxation tests, giving the true and lattice strains, insights into strain heterogeneities, and leading plasticity mechanisms. Moreover, two load–unload cycles were performed to deconvolute the different parts contributing to the signals. It is shown that though the samples were transversely isotropic (i.e., isotropic in the plane of the applied strains), the work-hardening properties are very different, the micro-plastic regime being greatly reduced in the equibiaxial test. This is illustrated with the elastic limits and with the fact that an equibiaxial test presents at equivalent von Mises strain higher stress relaxation and a decrease in strain heterogeneities.

International audience; The phenomena associated with strain-mediated multiferroic behavior have been quantitatively studied by combining synchrotron x-ray diffraction (XRD), ferromagnetic resonance (FMR) and macroscopic strain measurements (digital image correlation) in a magnetoelectric composite (Ni film on PZT substrate). The ferroelectric and piezoelectric strains have been studied by analyzing the evolution of x-ray patterns (peak intensities and shifts), while the magnetic response is studied by FMR (energy shift of the resonance), during in situ application of electrical voltage. Being given the intrinsic selective phase nature of XRD, the lattice strains have also been measured in the Ni film and have been found to be comparable to the macroscopic one (full transmission from the PZT substrate). The PZT strain has been successfully separated into two contributions, i.e. ferroelectric and lattice strains, the first one being five times higher than the second one. Moreover the last is itself composed of two sub-contributions: pure piezoelectric effect and ferroelectric strain in surrounding grains (strain transfer at grain boundaries). Finally, through in situ FMR measurements, we showed that the ferroelectric contribution to the strain-mediated magnetoelectric response is ten times higher than the pure piezoelectric one.

Synchrotron X-ray diffraction is a powerful tool to analyse the mechanical behavior of multiphase materials due to its selectivity. Simultaneous stress analysis of both phases of a W/Cu thin multilayer has been performed during a continuous biaxial loading on DiffAbs beamline at SOLEIL synchrotron (France). The use of a 2D detector with a large sample-detector distance is shown to give relatively accurate applied stress analysis even if only a small part of the usual ψ range of the sin2ψ method is considered. The results show the failure of the thin film multilayer while the W components are still under a strong compressive stress state of-3 GPa. It is concluded that the mechanical behavior is in fact mainly governed by the residual stress state.

X-ray strain pole figures (SPFs) have been capturedin situduring biaxial deformation of a gold ultra-thin film (thickness = 40 nm) deposited on a polymer substrate. An area detector was used to extract one line in the reciprocal space while the strained sample was rotated azimuthally step by step to produce the SPF. Such SPFs have been obtained for a textured anisotropic ultra-thin film under controlled non-equibiaxial loading using the SOLEIL synchrotron DIFFABS tensile device. The experimental setup allows the pole figure measurements of {111} and {200} reflections to be performed simultaneously. Interestingly, those two crystallographic directions are related to the two-extreme elastic mechanical behaviour. The full directional lattice strain dependence (SPF) is obtained within 15 min and can be monitored step by step upon loading. This procedure gives an insight into ultra-thin film mechanical response under complex biaxial loading.

WTi thin films are known as potential adhesion promoters and diffusion barriers. WTi thin films were deposited by magnetron sputtering from an alloyed target (W:Ti ~ 70:30 at.%). Real-time surface differential reflectance (SDR) spectroscopy and wafer-curvature measurements were performed during deposition to study the growth and the film continuity threshold. SDR measurements during WTi deposition allow the determination of the change in reflectivity of p-polarized light (at Si substrate Brewster's angle) between WTi film and Si substrate in order to monitor layer growth. The comparison between experimental and simulated WTi SDR signals assuming a homogeneous and continuous layer growth shows that film continuity is ensured beyond a thickness of 4.5 ± 0.2 nm. Real-time wafer-curvature measurements allow the determination of the intrinsic stress development in the film. Two regimes are noticed during the growth up to the development of a compressive steady state stress. The early stages of growth are rather complicated and divided into sub-regimes with similar boundaries revealed by both in situ techniques. Deposition of an interfacial continuous layer different from WTi bulk is suggested by both in situ techniques below a thickness of 4.5 nm.

In situ biaxial tensile tests were carried out on W/Cu nanocomposite thin films deposited on a polyimide cruciform substrate. A biaxial testing machine developed on the DiffAbs beamline at the French SOLEIL synchrotron allows for scrutinizing the mechanical behaviour of crystalline thin films at the micro-scale and the macro-scale using simultaneously synchrotron X-ray diffraction and digital image correlation techniques. Both strain analyses have been performed for two controlled non-equibiaxial loading paths: loading ratios of 0.8 and 0.33. The mechanical response is analysed and compared for the two loading ratios.

Tungsten-titanium (WTi) thin films are known as potential adhesion promoters and diffusion barriers. The barrier efficiency of WTi thin films against indium (In) diffusion was experimentally studied by x-ray diffraction (XRD) measurements during in situ annealing. Specific multilayered samples were designed to estimate the diffusion barrier properties using the Ni/In system. These diffusion samples were made up of a 100-nm-thick WTi layer prepared by magnetron sputtering from an alloyed target (W:Ti ≈ 70:30 at.%), sandwiched between Ni and Au/In layers. WTi film microstructures were observed to depend on the working pressure. Diffusion barrier breakdown was monitored upon annealing by the formation of intermetallic compounds (IMC) (intermixing between Ni and In). Annealing was performed at temperatures of 573 K, 623 K, and 673 K (homologous temperatures \(T/T_{\rm m}^{\rm In} \simeq 1.34, 1.45\), and 1.57, respectively) and under primary vacuum. The diffusion coefficients of In in WTi were determined. The correlation between WTi film microstructure and diffusion barrier efficiency was established. Better diffusion barrier performance was obtained for WTi films with dense microstructure associated with a compressive residual stress state. Hence, tuning the sputtering conditions allows significant improvement of barrier performance against diffusion through a change of the film microstructure.

International audience; A biaxial device developed at DiffAbs beamline of the SOLEIL synchrotron facility has been employed to determine the applied strains in film substrate composites using both X-ray diffraction and digital image correlation measurements. Such an experimental combination is used for the first time to determine the yield surface of a polycrystalline thin film deposited on a polyimide substrate. In situ biaxial tensile tests under different biaxial planar load ratios were performed on W/Cu nanocomposite thin films deposited on flexible substrates. The effect of loading path on the yield stress of W/Cu nanocomposites is presented by considering a large range of proportional loadings. By comparing experimental results with theoretical models, this study reveals the brittle behaviour of W/Cu nanocomposite thin films at small deformations.

In this paper, we have compressed a strongly {111}-fiber textured gold film deposited onto a pre-stretched polymer (Kapton) substrate. The elastic strains were measured using an in situ X-ray diffraction technique. We have performed strain analysis for two geometries called longitudinal and transverse. The Neerfeld–Hill model allows capturing with a few discrepancies the non-linear experimental curves obtained in the two configurations. In contrast, the evolution of the average of the longitudinal and transverse strains as a function of sin 2 Ψ is shown to be linear. This emphasizes the measurement accuracy during the compression test and is explained by the elastic grain-interaction independence of the averaged strains, even for a compression test. Moreover, we found that the gold film deforms elastically up to − 0.7% (about − 640 MPa).

International audience; When metals or alloys are oxidized at high temperature, an oxide film generally develops. Stress induced by oxide growth may influence the structure and the protective properties of the oxide scales. Classical models (taking into account elasticity and/or viscoplasticity and/or thermal mismatches) are able to predict some stress evolution. Moreover, the origin of that stress for isothermal condition must be sought-after in a growth strain related to the formation of the oxide above the substrate. In the present work, details are given on the modelling of stress under thermal loadings. The study is performed considering different thermomechanical behaviours and upgraded taking into account the origin of the different thermal couplings (weak and strong ones). Therefore, comparison with experimental results performed at ESRF allows extracting thermomechanical parameters with numerical values for different configurations (isothermal or with thermal evolution). This allows also investigating different mechanisms occurring at high temperature in chromia.

Copper-based high strength and high electrical conductivity nanocomposite wires reinforced by Nb nanotubes are prepared by severe plastic deformation, applied with an Accumulative Drawing and Bundling process (ADB), for the windings of high pulsed magnets. The ADB process leads to a multi-scale Cu matrix containing up to N = 854 (52.2 106) continuous parallel Nb tubes with diameter down to few tens nanometers. After heavy strain, the Nb nanotubes exhibit a homogeneous microstructure with grain size below 100 nm. The Cu matrix presents a multi-scale microstructure with multi-modal grain size distribution from the micrometer to the nanometer range. In-situ tensile tests of the nanocomposite wires under neutrons and high energy synchrotron beam shed light on the effects of the multi-scale microstructure and internal stresses on their macroscopic elastic-plastic properties, revealing that microstructure architecture offers an additional degree of freedom in the tailoring of materials properties.

An original experimental approach is presented to test under compression ultra-thin films on compliant substrates. The sputtering chamber was modified to permit deposition of the film on an untreated polyimide substrate tensily stressed by a Deben™ device. Exploration of the compression response was made possible with the film being loaded, when unloading the polyimide dogbone substrates. The compression response of an ultra-thin film of gold (18.5 nm) deposited onto the elastically loaded substrate was investigated using synchrotron X-ray diffraction. In contrast to tensile loading reported in the literature, the elastic compression could be explored up to − 0.5% (− 440 MPa as compared to 290 MPa).

Synchrotron x-ray radiation was used for in situ strain measurements in gold films on polyimide substrate during uniaxial deformation tests. We have used an area detector that allows inspecting multiple directions in the polycrystalline thin film without serial sectioning during straining. We show in this paper the configuration used and the attainable orientations on a pole figure for which the x-ray strains are measured. Moreover, we show the effect on the x-ray strains of the onset on plasticity, which was not detected by optical (macroscopic) strain measurement.

Residual-stress evolution in sputtered encapsulated ZnO/Ag/ZnO stack has been studied in-situ by synchrotron x-ray diffraction when heat treated. The ZnO/Ag/ZnO stack encapsulated into Si 3 N 4 layers and deposited on (001) Si substrates was thermally heated from 25 °C to 600 °C and cooled down to 25 °C. X-ray diffraction 2D patterns captured continuously during the heat treatment allowed monitoring the diffraction peak shifts of both Ag (15 nm thick) and ZnO (10 nm and 50 nm thick) sublayers. Due to the mismatch between the coefficients of thermal expansion, the silicon substrate induced compressive thermal stresses in the films during heating. We first observed a linear increase of the compressive stress state in both Ag and ZnO films and then a more complex elastic-stress evolution starts to operate from about 100 °C for Ag and about 250 °C for ZnO. Thermal contraction upon cooling seems to dominate so that the initial compressive film stresses relax by about 300 and 700 MPa after thermal treatment for ZnO and Ag, respectively. The overall behavior is discussed in terms of structural changes induced by the heat treatment.

In situbiaxial tensile tests within the elastic domain were conducted with W/Cu nanocomposite thin films deposited on a polyimide cruciform substrate using a biaxial testing machine developed on the DiffAbs beamline at the Synchrotron SOLEIL. The mechanical behaviour of the nanocomposite was characterized at the micro- and macroscales using synchrotron X-ray diffraction and digital image-correlation techniques simultaneously. Strain analyses for equibiaxial and non-equibiaxial loading paths were carried out. The results show that the two strain measurements match to within 1 × 10−4in the elastic domain for strain levels less than 0.3% and for both loading paths.

This paper illustrates the insights gained on the mechanical response of metal-coated soft polymer substrates using in-situ tensile testing under synchrotron x-rays. Progress made in external loading (uniaxial and biaxial) and detection capacities is reviewed since they allow scrutinizing multiphased specimens in a reasonable time frame. In general, the microstructure (grain morphology, preferential crystallographic orientation) has to be incorporated into the models used to interpret the experimental data.

Residual stress relaxation in sputtered ZnO films has been studied in-situ by synchrotron x-ray diffraction. The films deposited on (001) Si substrates were thermally treated from 25°C to 700°C. X-ray diffraction 2D patterns were captured continuously during the heating, plateau and cooling ramps. The corrections carried out for compensating the furnace drift are discussed. We first observe an increase of the intrinsic compressive stresses before stress relaxation starts to operate around 370°C. Then, thermal contraction upon cooling dominates so that overall, the large initial compressive film stresses turn to tensile after thermal treatment. The overall behaviour is discussed in terms of structural changes induced by the heat treatment.

The structure refinement is a challenge for conductors used for the winding of resistive coils producing non-destructive pulsed magnetic fields over 80T. These nanocomposite conductors composed of a conducting multiscale Cu matrix embedding Nb reinforcing nanofilaments are usually manufactured by using a Severe Plastic Deformation (SPD) process based on hot extrusion, accumulative cold drawing and bundling (ADB) steps [Thilly et al. Philos Mag A 82:925, 2002]. Equal-channel angular extrusion (ECAE) is investigated here as an alternative route since it may provide faster refinement to obtain the ultrafine structure needed for optimized electrical and mechanical properties of the conductors. Therefore, copper-niobium specimens obtained by hot extrusion were processed by ECAE at room temperature. The specific die of the ECAE tool used here is constituted by a round channel with three angles corresponding to a total equivalent strain of about 2.5. Deformed samples were examined by optical microscopy and characterized by hardness profiles and x-ray diffraction (texture pole figures). After one ECAE-pass, the shape of the samples is modified but no trace of damage appeared at the Cu-Nb interfaces. An increase of the hardness values localized in the copper matrix is revealed whereas the hardness of the niobium remains unchanged. Prior to ECAE, the hot extrusion process induced a fibre texture for both copper and niobium. Two fibre texture components were observed for copper: and . A single fibre texture component is evidenced for the niobium. After ECAE a significant variation of the texture is observed in relation with the strong shear induced by this process.

The objective of the present work is to study the elastic behaviour of composites exhibiting strong mechanical contrast components, namely, nanostructured metallic thin films deposited onto polymeric substrates. The stiff film/compliant substrate composites are submitted to complex stress fields during elaboration or applications and the use of a biaxial tensile device allows us mimicking the stress field of in-service thin films. The mechanical characterization of such structures and the relationship with the micro structure still require for further understanding both from fundamental and technological point of view. In such a way, the strain measurements at the macroscopic level have to be correlated with those at the microscopic level. In the present study, the applied strains were measured in situ both by X-ray diffraction (at the microscopic scale) and by digital image correlation (at the macroscopic scale). We used the biaxial testing machine dedicated to the DiffAbs beam line at the French synchrotron SOLEIL, which allows for controlling equi- or non-equi-biaxial loading on thin films supported by polymeric substrates. The metallic thin films were produced via Physical Vapour Deposition onto the centre of a cross-shaped polyimide substrate (Kapton®). The film-substrate composites were then deformed in the DiffAbs X-ray goniometer. Grain interaction models are very simple in the case of perfect local elastic isotropic materials such as tungsten. Such a material allows for directly comparing micro-strains (X-ray elastic strains) to macro-strains (DIC strains). The first results concerning W/Cu thin films deformed in situ with this biaxial testing machine are presented.

The present work has been conducted in order to determine systematically the influence of the spraying distance on the microstructure and mechanical properties of a Colmonoy 88 alloy deposited by means of HVOF thermal spray onto a SAE 1045 steel substrate. The spray distance varied between 380–470 mm and the evaluation of the deposits characteristics and properties was carried out both on their surface and on cross section. Both hardness and elastic modulus of the coatings were determined according to the model of Oliver and Pharr. The yield strength of the coatings was also estimated following the methodology developed by Zeng and Chiu for the analysis of the loading and unloading curves obtained from nanoindentation experiments, as well as from classical static spherical indentation tests. The microstructural analysis indicated a significant increase in the unmelted particles volume fraction and the development of interlamellar microcracks as the spraying distance increases, leading to a decrease in the elastic modulus of the coatings. Both hardness and elastic modulus showed an anisotropic behavior and were found to be higher on the cross section of the coating than on the deposition plane. A satisfactory comparison between the predicted and experimental values of the coatings yield strength was observed for all the conditions investigated.

International audience; The thermal stability of nanocomposite metals (a nanostructured copper matrix embedding niobium nanotubes) is investigated via time-resolved in situ annealing under synchrotron high-energy X-rays. The diffraction peak profile analysis demonstrates that internal-stress relaxation begins in the Nb nanotubes at a temperature far below the bulk recrystallization temperature and follows size-specific regimes originating from a proximity effect with the nanostructured Cu matrix: the increased Cu–Nb interface surface disrupts internal-stress relaxation processes, confirming the larger thermal resistance of nanostructured materials.

In situtensile tests have been carried out under synchrotron radiation on supported gold (Au) thin films exhibiting a pronounced crystallographic texture. The 2θ shift of X-ray diffraction lines has been recorded for different specimen orientations and several loading levels in the elastic domain. The data obtained demonstrate the large strain heterogeneities generated within the specimen because of the intergranular interactions associated with the large elastic anisotropy of Au grains. To interpret these results, the use of a multi-scale micromechanical approach is unavoidable. The theoretical background of such methods is described, and the points where exact results can be obtained and where approximations have to be introduced are highlighted. It is shown that the Vook–Witt model, for which a general formulation is provided, is the exact solution for polycrystals exhibiting a laminate microstructure, which is a significant departure from the standard thin-film microstructures. Among several standard models used in the field, the self-consistent model is the only one that reproduces the experimental data correctly. This is achieved by accounting for the actual crystallographic texture of the specimen, and assuming pancake-shaped two-point statistics for the morphological texture. A discussion of the limitations of this approach, originally developed for bulk materials, is given for the specific case of thin films.

International audience; Nanocomposite wires composed of a multi-scale Cu matrix embedding Nb nanotubes are cyclically deformed in tension under synchrotron radiation in order to follow the X-ray peak profiles (position and width) during mechanical testing. The evolution of elastic strains vs. applied stress suggests the presence of phase-specific elasto-plastic regimes. The nature of the elasto-plastic transition is uncovered by the "tangent modulus" analysis and correlated to the microstructure of the Cu channels and the Nb nanotubes. Finally, a new criterion for the determination of the macroyield stress is given as the stress to which the macroscopic work hardening, θa = dσa/dε0, becomes smaller than one third of the macroscopic elastic modulus.

Performing a completein situmechanical property analysis of polycrystalline thin films using X-ray diffraction is time consuming with most standard diffraction beamlines at synchrotron facilities and not realistic with laboratory diffractometers. Two-dimensional detection is shown to enable relatively fast and reliable X-ray strain measurements duringin situtensile testing of gold films deposited on polyimide substrates. Advantages and drawbacks in the use of two-dimensional detectors for this type of analysis are discussed for two commonly used geometries: reflection and transmission.

Mo(Cr) thin films were deposited by an Ionized Physical Vapor Deposition process i.e. Ionized Magnetron Sputtering (IMS). This deposition technique enables to ionize the neutral metallic sputtered species by a secondary plasma generated through a radio-frequency (RF: 13.56 MHz) powered coil. Thus, by acting on the substrate bias voltage, on the argon pressure and on the RF power applied to the coil, the ion energy and flux onto the substrate can be controlled. Various types of microstructure are then obtained, leading to a wide range of residual stresses in films from compressive to tensile. The control of both the microstructure and the related stress using the IMS process offers new opportunities in elaborating stress-engineered micro-objects for micro-electromechanical systems (MEMS). Residual stresses in the whole volume of the film were measured ex situ by Stoney curvature method and X-ray diffraction was applied to get the in-grain contribution (i.e. the crystallites) to the total residual stresses using the sin 2 ψ method. Besides, the grain morphology and local structure of the film were characterized by transmission electron microscopy. Relationship between synthesis conditions, microstructure, film morphology and residual stresses in Mo(Cr) films deposited by IMS is presented in this study and leads to a multi-scale description of the mechanisms of stress formation. The stress values determined from both techniques may be explained thanks to the analyzed morphological and microstructural features in the films.

Understanding the mechanical behavior of nano-structured thin films in relation to their microstructure, in particular to the grain size, is of utmost importance for the development of technological applications. Model nanometric W/Cu multilayers exhibiting different microstructures and supported by a (thin) polyimide substrate are elaborated. The films mechanical response is characterized experimentally by tensile tests carried out in-situ in an X-ray diffractometer installed at a synchrotron beam line. The orientation dependence of elastic strains and stresses is determined by an appropriate micromechanical model accounting for the material microstructure, and based on homogenization schemes. While a good agreement is globally found, the model better reproduces the experimental results of the W component than those of Cu, due probably to the elastic anisotropy of Cu grains. © 2007 Elsevier B.V. All rights reserved.

X-Ray diffraction (XRD) in combination with tensile testing is a very attractive tool for investigating the elastic behavior and further fracture or plasticity of metallic thin films and multilayers. Such studies are carried out with synchrotron X-ray sources allowing for several diffraction and loading conditions to be investigated and hence for great precision to be achieved. XRD is phase selective and allows for the study of individual layers or phase contributions. The method is based on a length scale change to relate in-grain elastic strains to tensile macro-stresses. Hence, it requires the modeling of the grain interactions in view of the structure of the films (morphology, texture). The paper is illustrated with studies carried out on elastically isotropic tungsten (W) films, elastically anisotropic gold (Au) textured films, and nanometric tungsten/copper (W/Cu) multilayers.