In situ hydrogen loading on zirconium powder

For the first time, various hydride phases in a zirconium-hydrogen system have been prepared in a high-energy synchrotron X-ray radiation beamline and their transformation behaviour has been studied in situ. First, the formation and dissolution of hydrides in commercially pure zirconium powder were monitored in real time during hydrogenation and dehydrogenation, then whole pattern crystal structure analysis such as Rietveld and Pawley refinements were performed. All commonly reported low-pressure phases presented in the Zr-H phase diagram are obtained from a single experimental arrangement

Time-of-Flight Three Dimensional Neutron Diffraction in Transmission Mode for Mapping Crystal Grain Structures

The physical properties of polycrystalline materials depend on their microstructure, which is the nano-to centimeter scale arrangement of phases and defects in their interior. Such microstructure depends on the shape, crystallographic phase and orientation, and interfacing of the grains constituting the material. This article presents a new non-destructive 3D technique to study centimeter-sized bulk samples with a spatial resolution of hundred micrometers: time-of-flight three-dimensional neutron diffraction (ToF 3DND). Compared to existing analogous X-ray diffraction techniques, ToF 3DND enables studies of samples that can be both larger in size and made of heavier elements. Moreover, ToF 3DND facilitates the use of complicated sample environments. The basic ToF 3DND setup, utilizing an imaging detector with high spatial and temporal resolution, can easily be implemented at a time-of-flight neutron beamline. The technique was developed and tested with data collected at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Complex (J-PARC) for an iron sample. We successfully reconstructed the shape of 108 grains and developed an indexing procedure. The reconstruction algorithms have been validated by reconstructing two stacked Co-Ni-Ga single crystals, and by comparison with a grain map obtained by post-mortem electron backscatter diffraction (EBSD)

The effect of residual stresses arising from laser shock peening on fatigue crack growth

Residual stresses have in the past been introduced to manipulate growth rates and shapes of cracks under cyclic loads. Previously, the effectiveness of shot peening in retarding the rate of fatigue crack growth was experimentally studied. It was shown that the compressive residual stresses arising from the shot peening process can affect the rate of crack growth. Laser shock peening can produce a deeper compressive stress field near the surface than shot peening. This advantage makes this technique desirable for the manipulation of crack growth rates. This paper describes an experimental program that was carried out to establish this effect in which steel specimens were partially laser peened and subsequently subjected to cyclic loading to grow fatigue cracks. The residual stress fields generated by the laser shock peening process were measured using the neutron diffraction technique. A state of compressive stress was found near the surface and tensile stresses were measured in the mid-thickness of the specimens. Growth rates of the cracks were observed to be more affected by the tensile core than by the compressive surface stresses

In-situ stress and strain measurements around cracks using synchrotron X-ray diffraction

High-energy synchrotron X-ray diffraction offers the unique combination of high spatial resolution and bulk material penetration power, which is well suited for the investigation of strain fields around cracks in engineering materials. The speed of data acquisition also lends itself to the observation of in-situ processes, such as crack propagation. This potential has been only partially explored over the last decade, and this paper reviews some basic advances with a view to future developments

Welding process impact on residual stress and distortion

Residual stress and distortion continue to be important issues in shipbuilding and are still subject to large amounts of research. This paper demonstrates how the type of welding process influences the amount of distortion. Many shipyards currently use submerged arc welding (SAW) as their welding process of choice. In this manuscript we compare welds made by SAW with DC gas metal arc welding, pulsed gas metal arc welding, Fronius Cold Metal Transfer (CMT), autogenous laser and laser hybrid welding on butt welds in 4mm thick DH36 ship plate. Laser and laser hybrid welding were found to produce the lowest distortion. Nevertheless a considerable improvement can be achieved with the pulsed gas metal arc welding and CMT processes. The paper seeks to understand the relationship between heat input, fusion area, measured distortion and the residual stress predicted from a simple numerical model, and the residual stresses validated with experimental data

Energy selective neutron radiography in material research

Energy selective neutron radiography was performed to describe a complex structure in polycrystalline materials. Experiments were performed with currently the highest energy and spatial resolutions achieved simultaneously, by employing a double crystal monochromator for selecting narrow energy bands from the initially polychromatic neutron beam and the neutron absorbing scintillator screen coupled with the cooled CCD camera as a detection system. It was shown that the detailed structure of the welded steel sample can be visualized and quantified by performing energy selective neutron imaging in the cold energy range, where elastic coherent scattering dominates the total cross section of the sample, showing characteristic Bragg edges. With the maps of crystallographic orientations over the sample area of similar to 2x2 cm(2) and thickness similar to 11.2 mm, obtained directly from radiographs, the complex structure was energy resolved with a spatial resolution of similar to 50 mu m

PVP2011-57786 STUDY OF RESIDUAL STRESSES HETEROGENEITIES IN A RING NOREM HARDFACED SAMPLE BY NEUTRON DIFFRACTION

ABSTRACT Iron-based hard-facing alloys, such as Norem, are considered to be good substitutes for Co-based ones where radiological activation is an issue. This work aims at studying residual stresses inside Norem02 Plasma Transferred Arc deposits. A standard test sample used by a valve manufacturer is taken as an example: it consists of a stainless steel (AISI 316L) disk with circular weld bead deposits of Norem hard-facing on both sides. Residual stresses were investigated using neutron diffraction on the ENGIN-X beam line. As expected, experimental results tends to indicate the welding overlap zones to be affected by reheating. Since previous works indicates quite limited metallurgical influence of high temperature re-heating on the deposited material, it is expected to be possible to capture this effect by further finite element modelling of the welding process, in order to study its influence on further in-service behaviour of valves

In situ crack growth studies of hydrided Zircaloy-4 on a single-edge notched tensile specimen

The strains in matrix and hydrides around a fatigue crack tip grown in situ in a single-edge notched specimen of hydrided Zircaloy-4 have been determined using synchrotron X-ray diffraction at various stages of loading. The hydride phase shows proportionally larger strains at full load compared to the matrix strain. The residual strains of the matrix ahead of the crack tip reveal the reverse plastic zone for a crack grown in tension, while the hydride residual strains remain strongly tensile. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved