OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Introduction A “new age” in the field of materials research is believed to have begun with the discovery of X-rays in 1895 and X-ray diffraction in 1912. This type of rays turned out to be a powerful tool for revealing structural features of materials at different scale levels. For a period of slightly more than 100 years, dozens of research methods based on the use of X-rays have been proposed. Most analytical instruments use X-ray tubes as radiation sources. The number of such devices produced in various countries is huge and it is very difficult to estimate it. Particle accelerators and specialized synchrotron radiation sources represent a special type of expensive and, by many parameters, unique analytical equipment. Synchrotron radiation (SR) is an electromagnetic oscillation created by ultrarelativistic electrons as it moves along a curvilinear path under the influence of a magnetic field. When moving along a circular orbit, the radiation has an intensity distribution in the form of a cone with a divergence angle -1 2 E mc γ = , rad. The maximum power of the emitted radiation is accounted for by the frequency: 3 max 2 3 2 E mc ν = , Hz where νmax is the radiation frequency; E is the total electron energy; m is the electron mass, c is the speed of light. By changing the electron path, it is possible to vary the maximum radiation in a wide range of the electromagnetic scale. Synchrotron radiation has a high degree of linear polarization in the plane of the electron orbit and a higher intensity compared to the radiation of X-ray tubes [1]. The first sources of SR were charged particle accelerators which produced a spurious synchrotron radiation. When revealing the advantages of synchrotron radiation and increasing the number of problems solved while using it, it turned out that it made sense to create specialized SR sources in which the analyzed radiation was not spurious, but main and useful. The unique parameters of SR determine its enormous advantages over other sources, including X-ray tubes. Higher photon fluxes provide higher resolution at an equivalent exposure time by reducing the size of the X-ray detector pixels or by changing the size of the X-ray beam. One of the methods based on the use of synchrotron or X-ray radiation is computed tomography (CT) which makes it possible to obtain images of the sections of the objects by processing multiple absorption X-ray patterns. When implementing the analyzed method, the computer ensures the operation of the X-ray source and processing of the data recorded by the detector. The advantages of using a synchrotron source with this method of image visualization include the parallelism of the rays, high radiation brightness values, that leads to reduction in data collection time and improvement in contrast when monochromatic radiation is used. With tomography it is possible to obtain three-dimensional pictures of objects for its further analysis. Computed tomography shows very good results when examining compact (isometric) samples. At the same time some limitations appear while implementing this research method. Firstly, the maximum possible access to the object of research is necessary to ensure the quality of the obtained images. The second limitation is related to the fact that in order to prevent excessive absorption of radiation the dimensions of the object have to be small. If these conditions are not met, artifacts appear in the images in the form of distortions that do not correspond to the real object. In order to reduce the number of artifacts that occur during the implementation of the computed tomography method, the sample should be stretched by a value less than the effective field of view of the 2D detector in all directions perpendicular to the rotation axis. Taking into account this circumstance, the analysis of cylindrical samples is the most rational [2]. These problems can be solved by using either the method of laminography or tomography with a limited angle. Meanwhile, the limited angle tomography method has disadvantages which were considered in the work of Helfen et al. [3]. The review presented below is focused on the synchrotron laminography method for the analysis of metal alloys.
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