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

例如，在增材制造或金属粉末压制中生产的金属材料的主要性质是孔隙率，其对部件的性质具有重要影响。表征和测试的一种非破坏性方法是微计算机断层扫描，但这是耗时的，并且仅分析部件的非常小的部分。基于光栅的X射线成像是一种很有前途的方法，以获得更多的目标信息，以传统的X射线成像。除了传统的衰减图像外，还可以使用两种物理效应来获得对比度：X射线波的相移（相位图像）和对象的颗粒或纤维结构的散射（暗场）。由此，暗场图像提供关于位于成像系统的分辨率极限以下的对象的结构的信息。这些信息可用于材料的无损检测，例如检测碳纤维增强塑料中的裂纹、检测材料中的空气夹杂物或区分颗粒尺寸。特别地，X射线暗场图像因此是金属材料的替代方案，以执行整个部件的非破坏性宏观检查，以获得关于微观结构的结构信息。例如，可以挑选出偏离所需微观结构标准太多的组件，并检测制造过程中的缺陷。 描述暗场信号与结构尺寸和分布的相关性的关键参数是相关长度。通过改变相关长度，这取决于结构特定的量，X射线能量和光栅之间的对象定位，可以得出关于样品的微观结构的结论。以前实现不同相关长度的方法使用X射线能量（具有射束硬化改变暗场信号的缺点）或对象位置（具有放大率改变的缺点）。在拟议项目中，应通过双干涉仪扫描仪实现微观结构的定量分析，该扫描仪通过两组光栅在一个装置中实现两种不同的相关长度。将对典型结构尺寸进行波场模拟，并与测量数据一起进行评估，以从金属半成品和部件中提取定量的子结构信息。

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.