Application of microLaue diffraction using a 3D energy-dispersive detector to study the evolution of fatigue damage in polycrystalline structural materialsy

工程结构合金通常是多晶多相合金，即由多个晶向和晶格结构不同的晶组成。许多材料的性能，如准静态强度和疲劳寿命，直接取决于颗粒之间的相互作用。晶界和相界是位错运动的障碍，决定了微结构疲劳短裂纹的扩展行为，并可能导致应力集中，最终导致裂纹的萌生，这是各向异性弹塑性变形的结果。微观技术，如扫描电子显微镜，允许显示表面的损伤，例如由疲劳载荷引起的损伤。应用高能同步束源的实验能够通过对少量反射的评估来确定表面和内部颗粒体积中的应力状况。一种新的创新和有前途的技术，打算在该项目的框架内进一步开发，用于表征疲劳损伤演化，即结合使用能量色散半导体面探测器的白束劳厄衍射。由于所有的布拉格角和反射能量可以同时确定，所以所有的反射都可以立即被索引。如果已知晶格结构，则还可以将反射分配给反射颗粒。然而，到目前为止，还不可能确定索引的颗粒的空间关系。在受损的谷物中，劳厄反射扩大。利用能量色散探测器，可以评估条纹的能量依赖性，并将其分配给特定的缺陷模式(位错簇、内应力、微裂纹等)。一旦出现一些方法论问题(粮食-粮食邻域关系、劳厄条纹的能量依赖分配、显微缺陷识别与X射线缺陷识别的相关性等)。白光劳厄衍射法将应用于工程材料。特别是，将研究单相和多相多晶材料在循环加载过程中的颗粒-颗粒相互作用。从所获得的结果中，将对微结构屏障的效率获得新的见解，从而使这些知识能够无误地应用于提高现代结构材料的疲劳抗力。

Engineering structural alloys are usually polycrystalline and multiphase alloys, i.e. they con-sist of many grains, which differ in crystallographic orientation and lattice structure. Many material properties, such as the quasistatic strength and the fatigue lifetime, depend directly on the interaction between the grains. Grain and phase boundaries represent obstacles for the dislocation motion, determine the propagation behaviour of microstructural short fatigue cracks, and may lead to stress concentrations and eventually to crack initiation as a conse-quence of anisotropic elastic and crystal-plastic deformation. Microscopic techniques, such as scanning electron microscopy, allow visualization of damage at the surface resulting for example from fatigue loading. Experiments applying high-energy synchrotron beam sources enable to determine the stress condition in the grain volume both at the surface and the interior by the evaluation of few reflexes. A new innovative and promising technique, which is intended to be developed further in the framework of this project for the characterisation of the fatigue damage evolution, is the white beam Laue diffraction in combination with the use of an energy-dispersive semiconductor area detector. Since all Bragg angles and reflex energies can be determined simultaneously, all reflexes can be indexed immediately. If the lattice structure is know, it is additionally possible to allocate the reflexes to the reflecting grain. However, thus far it is not possible to determine the spatial relationship of the indexed grains. In damaged grains, the Laue reflexes are expanded. By means of the energy-dispersive detector, the energy dependence of the streaks can be evaluated and assigned to specific defect patterns (dislocation clusters, internal stresses, microcracks, etc.). As soon as some methodical problems (grain-grain neighbourhood relationships, allocation of energy dependence of Laue streaks, correlation between microscopic and roentgenographic defect identification, etc.) have been solved, the white beam Laue diffraction method will be applied to engineering materials. In particular, the grain-grain interaction of singe-phase and multiphase polycrystalline materials during cyclic loading will be studied. From the results obtained, new insights on the efficiency of microstructural barriers will be gained enabling an unerring application of this knowledge to the increase of the fatigue resistance of modern structural materials.