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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. [ABSTRACT FROM AUTHOR]

(Received 5 July 2014; accepted 22 August 2014; published online 4 September 2014) Comparative studies of the mechanical behavior between copper, tungsten, and W/Cu nanocomposite based on copper dispersoïd thin films were performed under in-situ controlled tensile equi-biaxial loadings using both synchrotron X-ray diffraction and digital image correlation techniques. The films first deform elastically with the lattice strain equal to the true strain given by digital image correlation measurements. The Cu single thin film intrinsic elastic limit of 0.27% is determined below the apparent elastic limit of W and W/Cu nanocomposite thin films, 0.30% and 0.49%, respectively. This difference is found to be driven by the existence of as-deposited residual stresses. Above the elastic limit on the lattice strain-true strain curves, we discriminate two different behaviors presumably footprints of plasticity and fracture. The Cu thin film shows a large transition domain (0.60% true strain range) to a plateau with a smooth evolution of the curve which is associated to peak broadening. In contrast, W and W/Cu nanocomposite thin films show a less smooth and reduced transition domain (0.30% true strain range) to a plateau with no peak broadening. These observations indicate that copper thin film shows some ductility while tungsten/copper nanocomposites thin films are brittle. Fracture resistance of W/Cu nanocomposite thin film is improved thanks to the high compressive residual stress and the elimination of the metastable β-W phase. [ABSTRACT FROM AUTHOR]

WTi thin films were prepared from an alloyed target (W:Ti ∼ 70:30 at. %) by magnetron sputtering. Body-centered cubic WxTi1-x solid solutions with a {110} fiber texture and columnar grains have been produced with 0.75

Morphological and crystallographic structures of multilayered W/Cu nanocomposite thin films elaborated by physical vapor deposition were studied by varying copper and tungsten thicknesses. Sample examinations were performed by x-ray diffraction (XRD), grazing incidence small-angle x-ray scattering and transmission electron microscopy (TEM). Samples were found to be composed of copper nanoparticles, homogeneously dispersed in planes parallel to the film-substrate interface and periodically separated by tungsten layers along the growth direction. Our observations revealed an original texture development of the tungsten matrix from a mixture of unexpected α-W<111> and α-W<110> components to unique α-W<110> component as the copper coverage passes a thickness threshold of 0.6 nm. Local TEM texture stereology investigations revealed simultaneous columnar growth of both preferential orientations posterior to polycrystalline development while XRD reveals strong compressive residual stresses in both texture components. Physical origins of the preferential crystallographic orientation evolution are discussed. Copper mono layers adsorption on W surfaces promotes surface energy anisotropy and diminution which is effective over the threshold. Below, the presence of a W(Cu) solid solution which does not affect substantially the texture is revealed by the stress-free lattice parameter value extracted from XRD. [ABSTRACT FROM AUTHOR]

The short term oxidation behavior of γ-TiAl treated in low-concentration phosphoric acid solution has been investigated at 900 °C in air. A pyrophosphate film isomorphous to TiP2O7 is formed during the initial thermal treatment step and is responsible for a subsequent large reduction in the oxidation rate. During the initial course of oxidation at 900 °C, the pyrophosphate film transforms into a TiO2 solid solution containing phosphorus. This transformation impedes the usual oxides external growing mechanisms and leads to an internal development of the oxide scale with an associated reduced oxidation rate. [ABSTRACT FROM AUTHOR]

The elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in situ tensile tester in a four-circle goniometer on a synchrotron beam line (LURE facility, France). The mechanical description of the substrate-thin film composite structure has been developed to determine the stress tensor in the film while the strong {111} fiber texture was taken into account using the crystallite group method (CGM). CGM strain analysis allowed us to forecast the nonlinear relationship between strain and sin2 Ψ obtained for the thin films due to the strong anisotropy of gold. A least-square method was used to fit the overall experimental data with good accuracy and allows determining all single-crystal elastic constants. [ABSTRACT FROM AUTHOR]

Iron phosphate thin films have been obtained under controlled conditions by chemical conversion deposition. The films were formed on polycrystalline α-iron by immersion in acetone, as an organic solvent. After deposition, the films were investigated by x-ray photoelectron spectroscopy (XPS) and their influence on the thermal oxidation of α-iron was studied by means of in sim low incidence x-ray diffraction of synchrotron radiation. The study reveals interesting features related to the structure of both the phosphate and thermal oxide films. The XPS data suggest the iron phosphate to be constituted of long chains of phosphate groups PO[sup 3-, sub 4]; these groups being interconnected by Fe[sup 2+] and Fe[sup 3+] cations. X-ray diffraction measurements have shown a significant modification of the oxidation behavior of α-iron at 400 °C and atmospheric pressure, which is derived from the presence of the thin film: α-Fe[sub 2]O[sub 3] formation is clearly enhanced to the detriment of Fe[sub 3]O[sub 4], compared to the oxidation of pure iron in which Fe[sub 3]O[sub 4] is the dominant phase. As the growth rate of the α-Fe[sub 2]O[sub 3] layer is significantly reduced compared to that of Fe[sub 3]O[sub 4], thus the phosphated layers may find niche applications in low-to-moderate temperature environments. [ABSTRACT FROM AUTHOR]