Development of a two-interferometer-scanner for non-destructive analysis of microstructures in metallic components using X-ray dark-field imaging

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A major property of metallic materials produced in additive manufacturing or metal powder pressing, for example, is porosity, which has an important influence on the properties of the component. One non-destructive method for characterization and testing is micro-computed tomography, but this is time-consuming and only a very small section of the component is analyzed. Grating-based X-ray imaging is a promising way to obtain further object information to conventional X-ray imaging. In addition to the traditional attenuation image, two physical effects can be used to obtain contrast: the phase shift of X-ray waves (phase image) and the scattering by granular or fibrous structures of the object (dark-field). Hereby, the dark-field image provides information about structures of an object that lie below the resolution limit of the imaging system. This information can be used for non-destructive testing of materials such as detecting cracks in carbon fiber-reinforced plastic, detecting air inclusions in materials, or distinguishing particle sizes. Especially, the X-ray dark-field image is therefore an alternative for metallic materials to perform a non-destructive macroscopic examination of the entire component to obtain structural information about the microscopic structures. For example, components that deviate too much from the norm of the desired microstructure can be sorted out and defects in the manufacturing process can be detected. A crucial parameter describing a correlation of the dark-field signal with the structure sizes and distributions is the correlation length. By varying the correlation length, which is dependent on structure-specific quantities, X-ray energy and object positioning between the gratings, conclusions can be drawn about the microstructure of a sample. Previous approaches to realize different correlation lengths use the X-ray energy (with the disadvantage that beam hardening changes the dark-field signal) or the object position (with the disadvantage that the magnification changes). In the proposed project, the quantitative analysis of microstructures shall be enabled by means of a two-interferometer scanner, which realizes two different correlation lengths in one setup by means of two grating sets. Wave field simulations for typical structure sizes will be performed and evaluated together with measured data to extract quantitative substructure information from metallic semi-finished products and components.