J. Synchrotron Rad. (1997). 4, 147-154 Applications of High-Energy Synchrotron Radiation for Structural Studies of Polycrystalline Materials H. F. Poulsen, a S. Garbe, a T. Lorentzen, ~ D. Juul Jensen, ~ F. W. Poulsen, a N. H. Andersen, b T. Frello, b R. Feidenhans'P and H. Graafsma c aMaterials Department, Ris~ National Laboratory, DK-4000 Roskilde, Denmark, b Department of Solid State Physics, Riso National Laboratory, DK-4000 Roskilde, Denmark, and CEuropean Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France. E-mail: henning, friis.poulsen @ risoe.dk (Received 24 September 1996; accepted 31 January 1997) The large penetration power of high-energy X-rays (>60 keV) raises interesting prospects for new types of structural characterizations of polycrystalline materials. It becomes possible in a non- destructive manner to perform local studies, within the bulk of the material, of the fundamental materials physics properties: grain orientations, strain, dislocation densities etc. In favourable cases these properties may be mapped in three dimensions with a spatial resolution that matches the dimensions of the individual grains. Imbedded volumes and interfaces become accessible. Moreover, the high energies allow better in-situ studies of samples in complicated environments (industrial process optimization). General techniques for research in this energy range have been developed using broad-band angle-dispersive methods, on-line two-dimensional detectors and conical slits. Characterizations have been made at the level of the individual grains and grain boundaries as well as on ensembles of grains. The spatial resolution is presently of the order of 10-100 I, tm. Four examples of applications are presented along with an outlook. Keywords: high-energy synchrotron radiation; texture; residual stress; Bi-2223; solid-oxide fuel-cell concept (SOFC); industrial process optimization. 147 1. Introduction Dedicated beamlines for high-energy X-ray diffraction (>60keV) have recently become available at several synchrotrons. Their use for research on single crystals and amorphous materials is now established (cf. Schneider et al., 1994). In this report we focus on their applicability for studies of polycrystalline materials such as metals, alloys and ceramics. High-energy X-rays are associated with a large pen- etration power, which makes it possible to investigate millimetre- to centimetre-sized samples. This is crucial, as polycrystalline research is often concerned with struc- tural materials, where processing or application in general put restrictions on the sample dimensions. At the same time there may be unwanted surface effects, e.g. strain relaxation, corrosion, friction or atypical grain growth. The optimum X-ray energy, which is mostly a trade-off between penetration depth and photon flux, is for many applications with materials of medium atomic number, including steel, nickel, copper and various ceramics, in the range 60-100 keV. With state-of-the-art insertion devices, such as small- gap undulators at the APS (Shastri, Dejus, Haeffner & Lang, 1995), the available flux at 100keV may be as high as 2 x 1013 photons s-1 (0.1% bandwidth) -1 through a 5 x 2 mm pinhole at 30 m distance. The unique combi- © 1997 International Union of Crystallography Printed in Great Britain - all rights reserved nation of flux and penetration power raises prospects for performing local studies in the bulk of materials. This is obviously interesting for applications with imbedded volumes or interfaces, e.g. thick multilayers. Perhaps more importantly, the minimal gauge volume may in favourable cases be comparable with or smaller than the grain size. For the first time, it therefore becomes possible to measure non- destructively the fundamental microstructural parameters related to the individual grains: crystallographic orientation, strain, size, dislocation density, as well as the topology of the grain boundaries. Predictions of the macroscopic properties of the materials, such as texture, flow stress, fatigue strength, corrosion resistance, magnetization and superconducting critical current, depend heavily on these parameters. It therefore seems likely that being able to map the microstructure in three dimensions will signifi- cantly enhance our capability of predicting the macroscopic properties. Another important aspect of the large penetration power is the improved option for performing in-situ studies of samples in complicated environments. This is especially of interest for applied work (industrial process optimiza- tion). Finally, for some applications, including dislocation density measurements, it may also be of importance that the primary extinction vanishes, implying that kinematical models can be used. Journal of J~ynchrotron Radiation ISSN 0g0g-o4g5 ~'~I gg?