OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 0.9 , hkl K K D E (6) where σ is isotropic elastic stress; Ehkl – modulus of elasticity along the normal direction to the plane (hkl). In addition, the obtained data were analyzed using a model based on the assumption of the dislocation nature of crystal lattice distortions. This approach is called the modifi ed Williamson-Hall method [12]. In the case of cubic polycrystalline materials, the equation underlying this model has the following form: 2 2 00 2 ( ) / [1 ], h K W g a AC qH K (7) where α = (0.9/D)2; β – parameter that shows the probability of detecting stacking faults and twins; W(g) – coeffi cients depending on crystallographic direction indices [hkl] [13, 14]; a – lattice parameter; A – parameter depending on the average density of dislocations, the average length of the Burgers vector and the arrangement of dislocations; 00 h C – average dislocation contrast factor along [h00] direction; q – parameter depending on the elastic properties of the material; H2 = (h2k2 + h2l2 + k2l2) / (h2 + k2 + l2)2. According to literature, the modifi ed Williamson-Hall method has the lowest approximation error [11, 15]. A more detailed description of the implementation of this method is described elsewhere [11, 15, 16]. The microhardness of the samples was evaluated by using the Vickers method on a Wolpert Group 402MVD semi-automatic hardness tester. The load on the tetrahedral diamond indenter was 0.98 N, the holding time under load was 10 s. Research results It is believed that the multielement composition of high-entropy alloys leads to signifi cant distortions of its crystal lattice even before plastic deformation. This feature can possibly cause an additional broadening of the diffraction peaks of undeformed samples. In addition, the instrumental broadening of diffraction maxima arises due to the instrument which is used for the diffraction experiment. In order to take into account, the contribution of both factors and analyze only the effects caused by a change in the structure of the samples, an undeformed HEA sample of the same composition with a homogeneous structure was used as a reference. For this purpose, preliminary thermomechanical processing of HEA was carried out. This processing consisted in plastic deformation and subsequent long-term low-temperature annealing.According to the results shown in Fig. 1 a, b, the structure of the alloy after the deformation and low-temperature annealing is characterized by a more uniform spatial orientation of crystallites (which is evidenced by the presence of complete diffraction rings) and a low level of microstresses (which is evidenced by the small width of diffraction maxima). Subsequent cold rolling (Fig. 1, c, d) leads to a signifi cant broadening of the diffraction maxima, which indicates an increase in the number of defects in the crystalline structure. The peak profi le analysis of diffraction patterns of plastically deformed alloys makes it possible to estimate the number and the type of defects in the crystal structure based on the parameters of diffraction maxima. Thus, the assessment of the width of diffraction maxima using the classical Williamson-Hall method (Equation 5) makes it possible to determine the relative distortions of the crystal lattice and the CSRs sizes. However, it is known that this method is the least accurate with the signifi cant error of the approximation of experimental results. Therefore, some corrections based on the anisotropy of crystal properties are often introduced during the analysis of X-ray diffraction data by using the peak profi le analysis methods. The simplest way to account for anisotropy is to introduce into the calculation the elastic modulus for the normal to the planes (hkl) crystallographic directions (Equation 6). Table shows the values of the elastic moduli of the Al0.3CoCrFeNi alloy for the diffraction maxima analyzed in the work. Another, less common, but in many cases more effective way to improve the approximation accuracy is to use a model based on the dislocation theory of elastic distortions of the crystal lattice. This type of models is called modifi ed in the literature. They were described in detail in the works of
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