OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Fig. 12. Experimental setup for laminography of flat samples during stretching: 1 – X-ray detector; 2 – Rotating laminography platform; 3 – Electro-mechanical in-situ tensile machine; 4 – Optical microscope; 5 – Shear specimen (broken); 6 –Load cell (5 kN); 7 – Loading pin [29] analysis of the damage mechanisms leading to the final destruction of the loaded samples was carried out in the work. It was established that the process of material destruction was associated with the behavior of the intermetallic particles which were contained in it. Using the laminography method, the authors of the work identified two stages in the development of the destruction process. At the initial stage, a crack was formed inside the particle during the deformation process. This crack was perpendicular to the direction of maximum principal stress. Further, these cracks opened in the process of loading the sample that led to the appearance of large cavities. Combining the results of studies obtained by the methods of laminography and fractography of samples, conclusions were drawn about the mechanism of destruction of the alloy under external loading. The results of additional modeling by the REV (representative elementary volume) method showed that the opening of pre-cracked particles led to strain concentration at the mesoscopic level which ultimately led to the formation of strain bands. Visualization of pores developing during plastic deformation The work of Isshin Ando et al. [33] performed at the BL20XU station at the Spring-8 source (Japan) [34] can be mentioned as an example of visualization of pores that arise during the plastic flow of a material. The objects of study were samples obtained by sintering pure iron powder (JFE Steel Co., JIP301A). The porosity of the study objects (including open and closed pores) was 11.7 %. Samples with dimensions of 3×2×1 mm3 were deformed according to the tensile scheme. The equipment of the BL20XU station made it possible to conduct studies with a maximum spatial resolution of 1 µm for subsequent volume reconstruction with a minimum voxel size of 0.3 µm. The photon energy of a monochromatic X-ray beam generated by a double-crystal Si (111) monochromator cooled by liquid nitrogen was 37.7 keV. The axis of rotation of the sample was tilted at an angle of 45° to the X-ray beam. The detector was located at a distance of 18.0 mm from the center of rotation located on the surface of the sample. X-ray patterns with a diameter of 1,000 μm were obtained with an exposure of 300 ms at a rotation of 0.1° (for each image). The images were reconstructed by processing multiple X-ray patterns using a filtered back projection algorithm and rendered as 3D images using Avizo 9.1.1 software (FEI Co.). The SRCL method was used to analyze the initial (undeformed material) as well as samples deformed according to the tension scheme at a rate of 10–3 s–1. We studied five plastically deformed samples in different structural states (after deformation with different degrees). In the research a quantitative assessment of the pore configuration was carried out. The transformations of pores occurring at increased values of deformation were tracked using the methods of algebraic topology and persistent homology [35]. An approach based on the use of the laminography method made it possible to describe the process of coalescence of pores in iron samples obtained by powder metallurgy.
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