In previous studies, the crystal orientation has been characterized using electron backscatter diffraction (EBSD) on various Ni-based superalloys 21, 22. It is therefore essential to investigate the size, shape, microstrain/microstress, and defect density of the epitaxial dendrites at the sub-dendritic micrometric level. Previous studies also reveals changes in microstructural inhomogeneity from the center to the edge of dendrites 19, 20. What is more, the crystal orientation of the substrate can be preserved in the laser cladding layers, while the dendrites in the epitaxial zone are usually much finer than the traditionally cast alloys due to the high thermal gradient and fast solidification rate 18. The introduction of carbone leads to the formation of a variety of carbides, such as M 23C 6, M 6C, and MC 15, which could impose significant influence on the mechanical properties of Ni-based superalloy 16, 17. For example, hot cracking happens in the laser heating induced heat affected zones (HAZs) 13, 14. Albeit its unique advantages as a refurbishing technology, 3D printing is also facing some problems related to microstructural defects. Laser 3D printing is considered to be one of the most promising refurbishing technologies for extending the service lifetime and reducing overall cost of directionally solidified Ni-based superalloy blades and blisks 11, 12. To demonstrate this newly developed method, we take the laser assisted 3D printed Ni-based superalloy as an example.
Laue diffraction pattern Pc#
With this approach, the data analysis is greatly accelerated and can be easily accomplished on a regular PC in real time as the μXRD scan is conducted. Here, we develop a novel approach which takes the diffraction and background intensity into account to achieve rapid microstructural imaging. It is expected that this issue will become even more serious with the advent of nano-beam X-ray Laue diffraction achieving better spatial resolution 10, and for materials systems that are extremely non-uniform. These approaches usually take longer than the data collection for researchers who do not have access to fast parallel computing capabilities. Laue peak intensity is also taken into account for speeding the indexation process, unequivocally indexing trigonal crystal diffraction patterns 7, 8, and refining small molecule crystal structure 9. In a typical μXRD data analysis procedure 6, all the Laue patterns are indexed with one or several possible crystal structures to obtain the local crystal orientation, and then the positions of all the indexed Laue diffraction peaks in each pattern are compared with the calculated ones to derive the deviatoric lattice strain tensor. Albeit the large potential of materials characterization capabilities, μXRD data analysis is non-trivial.
Laue diffraction pattern crack#
Phase transformation can be detected at micro/nano scale 2, local crystal orientation and thus crystal grain boundaries mapped 3, elastic strain tensors measured at the subgranular scale 4, and plastic deformation around a crack tip investigated 5. With this technique, minute amounts of crystals in heterogeneous matrices can be identified 1. These studies usually involve two-dimensional raster scanning of an area of the sample, with recording of a Laue diffraction pattern at each scanning position. Laue microdiffraction (μXRD) using micro-focused high-intensity polychromatic X-ray beam obtained at synchrotron facilities, has found applications in a wide range of scientific disciplines such as materials, geological, and environmental sciences. Such analytical approach remains valid for a wide range of crystalline solids, and therefore extends the application range of the Laue microdiffraction technique to problems where real-time decision-making during experiment is crucial (for instance time-resolved non-reversible experiments). As an example, this method is applied to image key features such as microcracks, carbides, heat affected zone, and dendrites in a laser assisted 3D printed Ni-based superalloy, at a speed much faster than data collection. Visualization of the characteristic microstructural features is realized in real time during data collection. In this article, a novel approach is developed by plotting the distributions of the average recorded intensity and the average filtered intensity of the Laue patterns. In a typical experiment, a large number of Laue diffraction patterns are collected, requiring novel data reduction and analysis approaches, especially for researchers who do not have access to fast parallel computing capabilities. Synchrotron-based Laue microdiffraction has been widely applied to characterize the local crystal structure, orientation, and defects of inhomogeneous polycrystalline solids by raster scanning them under a micro/nano focused polychromatic X-ray probe.
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