OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 Introduction High-entropy alloys (HEAs) represent a new and promising class of materials that are attracting the attention of both scientists and engineers from all over the world. [1, 2]. The most common and studied are alloys based on a combination of cobalt, chromium, iron, nickel and an additional element. In particular, many scientifi c works are devoted to such alloys as CoCrFeMnNi (Cantor’s alloy) and AlxCoCrFeNi alloys [3–5]. Special attention of researchers attracts AlxCoCrFeNi alloys with x ≤ 0.3. Materials with this composition consist of only one face-centered cubic (FCC) phase. Such alloys have high ductility, excellent corrosion resistance and phase stability at high temperatures. At the same time, these materials possess low hardness and yield strength. The strength of these alloys can be signifi cantly improved by plastic deformation with subsequent heat treatment. According to a number of literary sources, the thermomechanical processing of the Al0.3CoCrFeNi alloy leads to its strengthening and an increase in hardness but allows retaining a reasonable level of ductility [6–8]. One of the effective methods for studying the structure of plastically deformed alloys is the peak profi le analysis of the X-ray diffraction patterns. This technique makes it possible to evaluate the defects in the crystal structure of alloys. The most common peak profi le analysis approach is the classical WilliamsonHall method. The use of this method makes it possible to estimate the distortions of the crystal lattice and the size of coherent scattering regions (CSRs). However, the Williamson-Hall method is known to have a high approximation error during the analysis of materials with high anisotropy of elastic properties. Therefore, special corrections are introduced during the analysis, that take into account the dependence of elastic properties on the direction in the crystal lattice. Even though these methods are widely used in the analysis of metals and alloys, there are no examples of exhaustive comparative analysis of peak profi le analysis methods for studying the structure of high-entropy alloys. In this study, several peak profi le analysis methods are compared by using the plastically deformed ingots of an Al0.3CoCrFeNi high-entropy alloy as an example. Using various methods, defects in the crystal structure were evaluated and its relationship with the microhardness of the deformed alloy was shown. Samples preparation. Methods for studying the structure and properties of materials In this work, the ingots of the Al0.3CoCrFeNi high-entropy alloy were used. The ingots were obtained from commercially pure metals by argon-arc melting in a water-cooled copper crucible. To distribute chemical elements evenly, 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 energy dispersive X-ray spectroscopy using a scanning electron microscope EVO50 XVP (Carl Zeiss) equipped with detector X-Act (Oxford Instruments). According to data obtained, the deviation of the actual composition did not exceed 0.6 at. %. It is well known that the structure of materials obtained by melting and casting methods is characterized by the presence of large dendrites, as well as a heterogeneity of the chemical composition (i.e., dendritic segregation). In order to obtain a more homogeneous composition and a fi ne-grained structure, thermomechanical processing of ingots was carried out. It was carried out by cold rolling with a reduction of 20 % and long-term low-temperature annealing (400 °C during 24 hours). The higher annealing temperatures were not used because some high-entropy alloys of the AlxCoCrFeNi system have a phase transition with formation of the B2 and L12 ordered phases (space group 3 ) Pm m at temperatures exceeding 400 °C [6, 9]. The results of X-ray diffraction analysis indicate that this thermomechanical processing contributed to the relaxation of the structure and did not lead to the formation of new phases (Fig. 1). After the thermomechanical treatment, the high-entropy alloy ingots were subjected to cold rolling with reduction of 20; 40; 60 and 80 %. The reduction during the single rolling pass was ~ 2 %. Afterall, the samples were cut for X-ray diffraction analysis and microhardness testing. The structure and properties of materials along the rolling direction (RD) и transverse direction (TD) were investigated.
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