OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 High expectations of the HEAs applicability are due to its high phase stability [7, 8]. It is known that HEA is characterized by the formation of phases with cubic crystal lattices [9, 10]. It was believed that the arrangement of atoms in the HEA structure is completely random, which should have determined its high mechanical and physical properties. However, recent studies have shown that HEAs contain additional phases, which are characterized by a regular, but not random, arrangement of atoms in the structure [11, 12, 13, 14]. These phases often appear in the HEA structure during prolonged thermal exposure [15, 16]. For example, it is known that in some alloys of the AlxCoCrFeNi system the B2 and L12 phases with primitive cubic lattice can be formed [17, 18, 19]. The AlxCoCrFeNi system is the most promising among all highentropy alloys due to the possibility of the phase composition fl exible control by changing the aluminum content. The study of strain-stress and thermal-stress states within workpieces obtained from high-entropy alloys is very important from the point of view of the application of these alloys. It is well known that the energy of plastic deformation is accumulated in the structure of metal alloys as the residual stresses. There are three types of internal stresses: macrostresses; microstresses and static lattice distortions [20]. These stresses have a signifi cant effect on the properties of the material. The using of HEAs as structural and functional materials requires scientists and engineers to understand the evolution of internal stresses within the crystalline phases of alloys. However, now in the literature there are no studies of residual stresses and residual lattice distortions of high-entropy alloys. The purpose of this work was to evaluate the residual lattice distortions of the phases of the AlxCoCrFeNi alloys after cold plastic deformation. The plastic deformation of Al0.6CoCrFeNi and AlCoCrFeNi alloys was carried out by using the axial compression scheme. The calculation of residual lattice distortions was based on synchrotron X-ray diffraction data. The results of this work allow drawing conclusions about the mechanical properties of the phases of high-entropy alloys. Methods and Materials In this work, the objects of research were ingots of Al0.6CoCrFeNi and AlCoCrFeNi high-entropy alloys. The ingots were obtained from pure metals by using argon-arc melting and cooling on a copper substrate. The shape of the ingots was close to cylindrical. The height of the obtained ingots was about 10 mm. The diameter was about 20 mm. For the most uniform distribution of chemical elements, remelting was carried out at least 10 times. Weight loss during smelting did not exceed 0.2 %. The elemental composition of the ingots was evaluated by X-ray microanalysis using a scanning electron microscope Carl Zeiss EVO50 XVP and Oxford Instruments X-Act detector. The fi nal value of the elemental composition was determined by averaging from at least twenty different regions of the ingot. The deviation of the composition from the nominal did not exceed 0.6 %. For further studies, cylindrical samples with a height of 8 mm and a diameter of 5 mm were cut from the ingots. The resulting cylinders were deformed according to the uniaxial compression scheme on a Instron 3369 machine. At a maximum applied stress of ~2,500 MPa, the deformation of the AlCoCrFeNi was 30 % and the deformation of the Al0.6CoCrFeNi was 53 %. Based on these values, the following compression degrees were chosen: 25; 34; 45; 50 and 53 % for the Al0.6CoCrFeNi and 12; 18 and 30 % for AlCoCrFeNi. Metallographic studies of the samples were carried out by the optical microscopy using a Carl Zeiss Axio Observer microscope. Before metallographic studies, the samples were subjected to etching with a solution consisting of a copper (II) sulfate, hydrochloric acid, and water (5 ml each). The crystal structure of the alloys was studied using the X-ray diffraction analysis. XRD experiments were carried out in a transmission mode at the beamline 5-A (X-ray microscopy and tomography) at VEPP-4 synchrotron source (Budker’s Institute of Nuclear Physics, Novosibirsk, Russia). The X-ray wavelength was 0.022 nm. A mar345s image plate 2D detector with pixel size 100 × 100 mkm2 and scan area diameter 345 mm was used to record the diffraction patterns. During the experiments, twodimensional diffraction patterns were obtained. These two-dimensional diffraction patterns were azimuthally integrated [21].
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