Pierre-Olivier Renault

Combined synchrotron X-ray and image-correlation analyses of biaxially deformed W/Cu nanocomposite thin films on Kapton

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

Benefits of two-dimensional detectors for synchrotron X-ray diffraction studies of thin film mechanical behavior

Performing a complete in situ mechanical property analysis of polycrystallinethin films using X-ray diffraction is time consuming with most standarddiffraction beamlines at synchrotron facilities and not realistic with laboratorydiffractometers. Two-dimensional detection is shown to enable relatively fastandreliableX-raystrainmeasurementsduringinsitutensiletestingofgoldfilmsdepositedonpolyimidesubstrates.Advantagesanddrawbacksintheuseoftwo-dimensional detectors for this type of analysis are discussed for two commonlyused geometries: reflection and transmission.1. IntroductionBoth theoretical and experimental studies have shown thatmaterials that have previously been examined at the micro-metre scale must be re-examined at the nanometre scale inorder to gain a full understanding of their physical properties.When grain sizes decrease to the nanometre scale, mechanicalproperties can be significantly altered from those of similarmicrometre-sized grains (Schiotz et al., 1999; Yip, 1998; VanSwygenhoven WCuenotetal.,2004; Spaepen& Yu, 2004). The processes responsible for these changes arebelieved to be caused mainly by an increase in grain-surfaceeffects and grain-boundary volumes, which become dominantover the bulk at the nanoscale. In a thin film, the changes canalso be caused either by the boundary conditions, whichbecome non-negligible for small film thicknesses at thesurface, at the film–substrate interface or at interfaces inmultilayers, or by constraints imposed by the substrate (Arzt,1998; Meyers et al., 2006). The study of elastic behaviorconsists in choosing a constitutive law using certain elasticconstants. X-ray diffraction is a well known technique used tomeasure very precisely elastic strains in crystalline materials(Hauk, 1997; Noyan & Cohen, 1987). By collecting individualdiffraction peaks or entire sections of diffraction patterns, it ispossible to obtain information about applied or residualmicro- and macro-strain as well as grain orientation (texture).As most crystalline materials are heterogeneous from themechanical point of view, X-ray strain measurements have tobe carried out for several directions, i.e. for different Braggpeaks or/and different lattice planes, to obtain reliable results.The diffractive determination of elastic constants using poly-crystallinesamplesrepresentstheinverseproblemtotheusualexperiment of classical X-ray diffraction residual-stressanalysis. Both problems are rather sensitive to the quality ofthe experimental data and to the micromechanical models.Micromechanical models, such as the self-consistent model,can predict inter-granular effects by accounting for themechanical anisotropy and the texture of the polycrystal(Matthies et al., 2001; Matthies & Humbert, 1995; Bunge et al.,2000). Grain interaction models can be relatively simple for atexture-free case and for a cubic crystal symmetry (Do¨lle,1979), and the so-called sin

Size effects on the Mechanical Behavior of Nanometric W/Cu Multilayers

The mechanical behavior of nanostructured stratified W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. Polycrystalline materials have already been constructed through the Voronoi method and thanks to TEM observations. Atomistic simulation and calculation are underway to validation.

Modelling of the Mechanical Behaviour of a Chromia Forming Alloy Under Thermal Loading

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.

Relaxation mechanisms in a gold thin film on a compliant substrate as revealed by X-ray diffraction

The fact that the polymeric substrate does not relax after a load jump allows realizing an original relaxation experiment of a metallic thin film. Thanks to the combination of two strain probes done at different scales, namely, X-ray synchrotron diffraction and digital image correlation techniques, the apparent activation volumes are monitored and their values help to capture leading deformation mechanisms in thin films. Such experiments have been performed on a nanocrystalline gold thin film, and deformation mechanisms involved during a biaxial straining have been distinguished between different texture components.

Development of a biaxial tensile module at synchrotron beamline for the study of mechanical properties of nanostructured films

We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine with synchrotron standard for in-situ diffraction characterization of thin polycrystalline metallic film mechanical response. The machine has been designed to test cruciform substrates coated by the studied film under controlled applied strain field. Technological challenges comprise the fixation of the substrate, the generation of a uniform strain field in the studied (central) volume, the operations from the beamline pilot. Tests on W and W/Cu multilayers films deposited on polyimide substrates are presented.

Residual Stresses in Sputtered ZnO Films on (100) Si Substrates by XRD

Residual stresses in sputtered ZnO films on Si are investigated and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films encapsulated or not by Si 3N4 protective coatings are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After a heat treatment at 800°C, ZnO films are tensily stressed while ZnO films encapsulated by Si 3N4 are stress-free. With the aid of in-situ X-ray diffraction, we argue that this thermally-activated stress relaxation can be attributed to a variation of the chemical composition of the ZnO films.

X-ray Diffraction Study of the Mechanical Elastic Properties of Nanometric W/Cu Multilayers

The mechanical behavior of W/Cu multilayers with a period of 24 nm and a 1/3 W/Cu thickness ratio prepared by magnetron sputtering was analyzed using a method combining X-ray diffraction and tensile testing. Tests were performed both with a conventional and a synchrotron light source to analyze the elastic response of the system. Comparison between the strain-load curves obtained in both experimental conditions and estimated curves clearly shows that high quality synchrotron measurements are a preliminary condition for size-effect studies. Moreover, cyclic tests were used to determine the elastic domain of each material and compare their mechanical responses. Plastic strain was observed in copper before in tungsten layers in accordance with the mechanical behavior of their bulk counterparts.

Size Effect in the Plasticity of Multiscale Nanofilamentary Cu/Nb Composite Wires During in-situ Tensile Tests Under Neutron Beam

Copper-based high strength nanofilamentary wires reinforced by bcc nanofilaments (Nb or Ta) are prepared by severe plastic deformation for the winding of high pulsed magnets. In-situ tensile tests under neutron beam were performed on a Cu/Nb nanocomposite composed of a multiscale Cu matrix embedding 55 4 Nb filaments with a diameter of 267 nm and spacing of 45 nm. The evolution of elastic strains for individual lattice plane in each phase and peak profiles in the copper matrix versus applied stress evidenced the co-deformation behavior with different elastic-plastic regimes and load sharing: the Cu matrix exhibits size effect in the finest channels while the Nb nanowhiskers remain elastic up to the macroscopic failure, with a strong load transfer from the copper matrix onto zones that are still in the elastic regime. Taking into account results from residual lattice strains also determined by neutron diffraction, the yield stress in the finest Cu channels is in agreement with calculations based on a single dislocation regime.

Damage in High Energy Light Ions Irradiated Silicon Carbide

Commercial n-type 4H-SiC wafers were implanted with doses of MeV alpha particles, high enough to cause majority carrier modification. Analysis of infrared reflectivity spectra shows that the implanted crystals can be divided into three layers: a surface layer of about 30 nm followed by a compensation layer where the energy transfer of the incident particles is low and an overdoping layer in the region of maximum defect production, i.e. near the theoretical mean range of ions R p