Three-Dimensional X-Ray Structural Microscopy Using Polychromatic Microbeams
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Three-Dimensional
X-Ray Structural Microscopy Using Polychromatic Microbeams
Gene E. Ice and Bennett C. Larson Abstract In this article, the authors describe the principle and application of differential-aperture x-ray microscopy (DAXM). This recently developed scanning x-ray microprobe technique uses a confocal or traveling pinhole camera approach to determine the crystal structure, crystallographic orientation, and elastic and plastic strain tensors within bulk materials. The penetrating properties of x-rays make the technique applicable to optically opaque as well as transparent materials, and it is nondestructive; this provides for in situ, submicrometer-resolution characterization of local crystal structure and for measurements of microstructure evolution on mesoscopic length scales from tenths to hundreds of micrometers. Examples are presented that illustrate the use of DAXM to study grain and subgrain morphology, grain-boundary types and networks, and local intra- and intergranular elastic and plastic deformation. Information of this type now provides a direct link between the actual structure and evolution in materials and increasingly powerful computer simulations and multiscale modeling of materials microstructure and evolution. Keywords: deformation, microdiffraction, polychromatic microbeams, three-dimensional differential-aperture x-ray microscopy (DAXM).
Introduction Most solid materials are crystalline, with grain sizes ranging from nanometers to hundreds of micrometers. The misoriented grains of polycrystals are connected by networks of grain boundaries with distinct local crystallography and anisotropic physical properties. Understanding the behavior of polycrystalline materials under thermal, mechanical, chemical, and electrical stresses and predicting the consequences of advanced technological processing techniques represent a longstanding materials research goal.1–3 Despite remarkable progress, predicting new materials, microstructure, and evolution is not yet possible. Finite element modeling (FEM) using constitutive relations and continuum 170
mechanics has revolutionized the design and manufacture of structural components over length scales where mesoscopic structure can be ignored.4 The development of analogous theory and modeling capabilities for mesoscopic length scales has proven to be extremely difficult because of the complex and collective inter- and intragranular microstructural interactions.4–6 Transmission electron microscopy (TEM) provides detailed microstructural information on thin-section samples,6,7 and electron backscattering diffraction (EBSD) is readily available8,9 for micrometer- and submicrometer-resolution surface structure, microstructure, and deformation measurements. However, these thin-section and
surface tools are not designed for detailed testing of computer simulations and multiscale modeling of the evolution of materials microstructure in three dimensions. Direct, nondestructive measurements are needed of the local microstructure and evolution in the interio
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