S.F. Nielsen

Three-dimensional maps of grain boundaries and the stress state of individual grains in polycrystals and powders

A fast and non-destructive method for generating three-dimensional maps of the grain boundaries in undeformed polycrystals is presented. The method relies on tracking of micro-focused high-energy X-rays. It is verified by comparing an electron microscopy map of the orientations on the 2.5 × 2.5 mm surface of an aluminium polycrystal with tracking data produced at the 3DXRD microscope at the European Synchrotron Radiation Facility. The average difference in grain boundary position between the two techniques is 26 µm, comparable with the spatial resolution of the 3DXRD microscope. As another extension of the tracking concept, algorithms for determining the stress state of the individual grains are derived. As a case study, 3DXRD results are presented for the tensile deformation of a copper specimen. The strain tensor for one embedded grain is determined as a function of load. The accuracy on the strain is Δ∊ ≃ 10−4.

Measurements of plastic displacement gradient components in three dimensions using marker particles and synchrotron X-ray absorption microtomography

Abstract A universal method is presented for characterising the three-dimensional (3D) plastic displacement gradient field in bulk materials that contain particles or voids observable by X-ray tomography. Millimetre sized samples are investigated by absorption contrast microtomography using high intensity X-rays from a synchrotron source. The positions of dispersed marker particles are determined as a function of imposed strain. The particle diameter can be in the micrometre range, and the volume fraction can be less than 1%. The method is demonstrated by evaluation of compression deformation of a cylindrical Al specimen containing W marker particles. By interpolating the displacement gradient components determined at each particle on a 30×30×30 μm 3 grid, 3D maps of the displacement gradient components are obtained with a resolution of 10 −2 in each component. Limitations of the method are discussed, and the potential for application in materials science is outlined.

A three-dimensional X-ray diffraction microscope for deformation studies of polycrystals

The microstructure in polycrystalline materials has mostly been studied in planar sections by microscopy techniques. Now the high penetration power of hard X-ray synchrotron radiation makes three-dimensional (3-D) observations possible in bulk material by back tracing the diffracted beam. The three-dimensional X-ray diffraction (3DXRD) microscope installed at the European Synchrotron Radiation Facility in Grenoble provides a fast and non-destructive technique for mapping the embedded grains within thick samples in three dimensions. All essential features like the position, volume, orientation, stress-state of the grains can be determined, including the morphology of the grain boundaries. The accuracy of this novel tracking technique is compared with electron microscopy (EBSP), and its 3-D capacity is demonstrated.

Growth kinetics of individual grains during recrystallization with an intermediate cooling cycle

Abstract The growth of individual grains in commercial aluminium (AA5182) was measured in situ during a recrystallization heat treatment at 543 K including an intermediate cycle to room temperature and back on the three dimensional X-ray diffraction microscope at the European Synchrotron Radiation Facility. It is shown that the growth kinetics of the individual grains were not affected by the intermediate cycle to room temperature.

Metal Microstructures in Four Dimensions

By Three Dimensional X-ray Diffraction (3DXRD) microscopy it is possible to characterize microstructures non-destructively in 3 dimensions. The measurements are furthermore typically so fast that dynamics may be monitored in-situ, giving also the 4th dimension, namely the time. The 3DXRD technique is based on diffraction of high energy x-rays from third generation synchrotron sources. In the present paper the 3DXRD technique is described and it’s potentials are illustrated by examples relating to elastic and plastic strains, recovery, recrystallization and grain growth.Copyright

Dislocation Boundaries and Slip Systems in Uniaxially Deformed Crystals

The dislocations in the extended planar dislocation boundaries formed during deformation are generated by the active slip systems. Investigation of the boundaries is therefore a tool to obtain information on the active slip systems. Here, the orientation of the dislocation boundaries in uniaxially deformed aluminum poly- and single crystals are compared. It is found that the single crystal boundary planes are consistent with those found in polycrystals, indicating that the active slip systems in single and polycrystals are the same. However, boundaries are closer to the slip planes in the single crystals. This is taken as an indication that the secondary slip systems are more active in the polycrystal. The orientation of the boundary plane varies with the crystal orientation in a way that is consistent with activation of the five most stressed slip systems.