Papers by Keyword: Synchrotron

Abstract: Austenitic stainless steel (SUS316L) was used as specimen material, and the plate specimens were deformed plastically with a wide range of strain rates (6.67×10^-5~ 6.70×10²/s). The residual micro-stress for each lattice plane was measured with hard synchrotron X-rays. The residual macro-stress due to tensile deformation depended on strain rate. The residual micro-stresses varied from tension to compression, depending on the diffraction elastic constant. The soft lattice plane had tensile residual stress, and the hard lattice plane had compressive residual stress. The higher the strain rate, the smaller the difference in residual micro-stresses. The residual micro-stresses of the surfaces peened with the laser-peening or water-jet-peening were examined. Both surfaces had exhibited large compressive residual stress. The residual micro-stress on the peened surfaces showed a tendency opposite to residual micro-stress due to tensile deformation.

Abstract: The present study is dedicated to high energy x-ray diffraction measurements of residual stress at bone-implant interfaces. Bone regeneration is different from soft tissue repair as scar formation never occurs and as de novo bone tissue is produced with proliferation and differentiation of mesenchymal cells. To start the bone remodelling, the stress – the most important mechanical factor – should stimulate the osteocytes. Osseointegration is also observed with non-functional implants, in particular with dental implants. This means that a stress similar to a residual stress must exist.

Abstract: Grain tracking is a term used to describe experiments that investigate polycrystalline materials in terms of the crystallites or grains from which they are composed, non-destructively and in three dimensions. The new German high brilliance synchrotron radiation source, Petra III, will become available to users in 2010 [1]. The GKSS research centre will operate two beamlines, including the high energy materials science beamline (HEMS) [2]. HEMS will feature an instrument dedicated to grain tracking, able to support a range of experiments of this kind. This paper describes the design and specification of this instrument, and gives examples of the types of experiments that will be possible.

Abstract: As the top coating, zirconia with 4 mol% yttria was electron beam-physical vapor deposited (EB-PVD) on the bond coating of CoNiCrAlY. The substrates were rotated during EB-PVD process and the rotation speeds were 5 (R5) and 10 rpm (R10). The thickness of the top coating was 0.12 mm. In order to investigate the change of the internal stress in the top coating under a heat cycle, the specimen was heated from a room temperature to 1293K, the internal stress was measured in-situ by a strain scanning method with hard synchrotron X-rays at each temperature step. For the specimen R5, the internal stress increased from about -100 MPa to about 100 MPa with the increase in temperature, then the stress relaxation of the top coating occurred over 1093K. In the cooling process, the internal stress decreased, however, the changing rate of the internal stress was small as compared with the heating process. This was caused by the feather-like structure sintered. For the specimen R10, the internal stress did not show a tension in the heating process, it was caused by the separation between columnar structures.

Abstract: We report on the optical and mechanical properties of Si3N4 inclusions, formed in the upper part of mc-Si blocks during the crystallization process. Those inclusions usually appear as crystalline hexagonal tubes or rods. Here we show that in many cases the Si3N4 inclusions contain crystalline Si in their core. The presence of the Si phase in the centre was proven by means of cathodoluminescence spectroscopy and imaging, electron beam induced current measurements and Raman spectroscopy. The crystalline Si3N4 phase was identified as β-Si3N4. Residual stress was revealed at the particles. While the stress is compressive in the Si material surrounding the Si3N4 particles tensile stress is found in the Si core. We assume that the stress is formed during cool down of the Si block and is a consequence of the larger thermal expansion coefficient of Si in comparison to that of β-Si3N4. Iron assisted nitridation of Si at temperatures below 1400 °C is considered a possible mechanism of Si3N4 formation.

Abstract: The X-ray stress measurement with synchrotron radiation (SR) and an image plate (IP) was conducted using the facility of the Photon Factory (PF) of the High Energy Accelerator Research Organization (KEK). The influence of 2θ on stress measurement with the cosα method was investigated. The experiments were conducted under the conditions of 2θ=170 deg, 156.4 deg and 127 deg respectively. It was found that the hypothesis on the relation between the accuracy and the diffraction angle in the X-ray method is not valid in case of the cosα method.

Abstract: Neutron and synchrotron strain or stress evaluations are reliable when the probe volume is completely immersed in the studied material. However, acquisitions carried out close to interfaces are much more difficult to analyze. Under these conditions, it is indeed very difficult to characterize precisely the volume analyzed by the radiation and finally to define the measured depth. To solve this problem, a complete Monte Carlo simulation of neutron spectrometers and synchrotron experiments has been developed. This method allows defining precisely the size and shape of the probe used. It permits then predicting the evolution of the diffracted intensity versus the position of this volume in the matter. The calculations finally let to define the real analyzed depth, accounting for the local conditions of diffraction and absorption in the material. The method is illustrated by neutron and synchrotron experiments carried out to characterize stress fields existing close to interfaces. The simulations also permit predicting the shape of diffraction profiles that would be observed on perfect specimens. Such information can then be used to correct the instrumental broadening existing in real experiments. This allows a fine Fourier analysis of the diffraction peaks recorded for several orders of reflection and finally permits defining the mean size of the crystallites and the root mean squares of the strains of second and third kind. Such information is useful to characterize and analyze the mechanical behavior of materials.

Abstract: The orientation changes during heating of extruded AZ31 were investigated using synchrotron Xrays by in-situ experiments. The as-extruded sample shows a strong <10.0>-fiber texture which is generally observed after round extrusion. The initial <10.0>-fiber texture, in which the <10.0> direction of the hexagonal crystallites is parallel to extrusion direction, starts to change to <11.0>- fiber component at 300 °C. The orientation change rate shows an exponential relation to the heating temperature and the soaking time. The microstructure observations, prior and post heat treatment, indicate that the texture changes occur mainly during grain growth.

Abstract: The present study presents the relevance of X-ray diffraction analysis using synchrotron light in the identification of phases with low intensity peaks. Niobium sheets were coated with monetite and then converted to hydroxyapatite in an alkali solution. Octacalcium phosphate was identified as an intermediate phase in the conversion monetite-hydroxyapatite.

Abstract: The solid microstructure built in the solid governs the properties of materials elaborated from the melt. In order to clarify the dynamical mechanisms controlling solidification processing, we use in situ and real-time synchrotron X-ray radiography at ESRF (European Synchrotron Radiation Facility) to analyze microstructure formation in thin aluminum alloys solidified in the Bridgman facility installed at the ID19 beamline. During directional solidification of Al - 3.5 wt% Ni alloys, global mechanical constraints induced by the shape are found to act on the solid microstructure. In particular, radiography videos of dendritic growth show disorientations of sidebranches induced by mechanical stresses. In the solidification of AlPdMn quasicrystals, live imaging reveals that facetted growth proceeds by the lateral motion of ledges at the solid-melt interface. When the solidification rate is increased, the kinetic undercooling becomes sufficient for grain nucleation and growth in the liquid. These grains develop specific features that can be attributed to grain competition and concomitant poisoning of growth caused by the rejection of aluminum in the melt.