Papers by Author: Nobumichi Tamura

Abstract: Ni-30Cr and Fe-47Cr alloys have been oxidized at 900 and 1000°C in air. The influence of the oxidation and cooling conditions on the magnitude of residual stresses present in the oxide scale as well as the existing relaxation modes are studied. A rigorous determination of the residual stresses at both macroscopic scale in the oxide film adherent to the substrate and local scale over the damaged areas allows a comparison with models describing thin film delamination. A multi-scale approach is then proposed : Residual stress levels are determined thanks to conventional x-ray diffraction and Raman spectroscopy while mappings are done over different types of buckling using Raman micro-spectroscopy and synchrotron micro-diffraction. Additional morphological information combined to associated stress levels is injected in the mechanical laws for buckling in order to extract the interfacial toughness.

Abstract: X-ray diffraction is used in combination with tensile testing for measuring elastic properties of metallic thin films. Size effect, elastic anisotropy and grain morphologies are considered in all these experiments and supported by different kind of numerical simulations operating at different length scales. Such instrumental studies are time consuming even if synchrotron sources are used. New experiments are under progress for reducing acquisition data and improving precision on strain measurements. After introducing briefly the main principles and results of our techniques, first promising measurements on nanometric W/Cu multilayers using 2D CCD detectors and high monochromatic flux at the Advanced Light Source Berkeley (USA) on beam line 11.3.1 are presented. In addition, simulation experiments for analyzing elasticity in textured gold film are discussed.

Abstract: The overall plastic behavior of polycrystalline materials strongly depends on the microstructure and on the local rheology of individual grains. The characterization of the strain and stress heterogeneities within the specimen, which result from the intergranular mechanical interactions, is of particular interest since they largely control the microstructure evolutions such as texture development, work-hardening, damage, recrystallization, etc. The influence of microstructure on the effective behavior can be addressed by physical-based predictive models (homogenization schemes) based either on full-field or on mean-field approaches. But these models require the knowledge of the grain behavior, which in turn must be determined on the real specimen under investigation. The microextensometry technique allows the determination of the surface total (i.e. plastic + elastic) strain field with a micrometric spatial resolution. On the other hand, the white beam X-ray microdiffraction technique developed recently at the Advanced Light Source enables the determination of the elastic strain with the same spatial resolution. For polycrystalline materials with grain size of about 10 micrometers, a complete intragranular mechanical characterization can thus be performed by coupling these two techniques. The very first results obtained on plastically deformed copper and zirconium specimens are presented.

Abstract: A scanning X-ray microdiffraction beamline using white or monochromatic beam has been recently made available to the user’s community at the Advanced Light Source, Berkeley, USA. Samples are scanned under an X-ray beam with size ranging from 15 microns down to less than a micron, and 2D diffraction patterns are collected at each step. A specifically written software allows for the full treatments of these patterns to obtain as outputs high spatial resolution grain orientation, strain/stress or mineral species distribution maps. The range of applications of this technique goes from the study of the mechanical properties of thin films to the understanding of trace elements speciation in environmental sciences.

Abstract: In-situ measurement of local orientation and strain Has Been carried out for a copperpolycrystals under a uniaxial loading using a synchrotron x-ray microdiffraction method at the Advanced Light Source. The heterogeneities of deformation-induced microstructure within single grains were observed. There were differences in the selection of simultaneously acting slip systems among neighboring volume elements within a grain.