Review of alloys developed using the entropy approach

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 increased, the volume fraction of the s -phase decreased. Of the three high-entropy materials studied, the VCrMnFeCoNi1 alloy has the highest level of wear resistance. Its coefficient of relative wear resistance (K = 3.03), measured in accordance with GOST 3647-80, is close to the value of the material deposited with the T-590 electrode (K = 3.09), which is used for surface hardening of products operated under conditions of abrasive wear. Thus, it can be concluded that the high-entropy VCrMnFeCoNi1 alloy proposed in [103] has a high abrasive wear resistance. In [23], using the example of a high-entropy VNbTaCrMoW alloy, it is concluded that the material acquires averaged values of most physical characteristics. The only exceptions include strength properties, which are significantly higher in HEAs due to the anomalous values of solid solution hardening [118, 119]. Plastic deformation of the HEAs Along with heat treatment, plastic deformation is considered as one of the most effective technological factors that allow changing the structure, strength, ductility, and other properties of high-entropy alloys. At present, there is no reason to say that the potential possibilities of such an approach are obvious and can be applied to most of the analyzed materials. At the same time, when studying a number of polymetallic al- loys, convincing evidence of the effectiveness of methods for processing metals by pressure was obtained. For example, after cold rolling with a degree of 80%, the CoCrFeMnN(Al, C) alloy has a high complex of mechanical properties: s 0.2 = 870 MPa, s u = 1,060 MPa, d = 25 % [21]. The result of hot plastic deforma- tion of the CoCrFeNiMnV alloy is a change in its phase composition and the transformation of the original lamellar structure into an ultra-fine-grained one, which has a favorable effect on the properties of the mate - rial, in particular, leads to a decrease in the temperature of the visco-brittle transition [82]. Research focused on filling the gaps in the field of plastic and thermoplastic impact is successfully car - ried out at the Belgorod State National Research University under the leadership of G.A. Salishchev. One of the tasks solved in D.G. Shaisultanov’s thesis work was related to the development of deformation modes that provide an increase in the complex of mechanical properties of CoCrFeNiMn and CoCrFeNiAlCu al- loys [82]. It has been experimentally established that at room temperature, CoCrFeNiMn alloy blanks can be formed by uniaxial rolling without losing the continuity of the material by tens of percent. As a result of this impact, the yield strength of the alloy increased by 8 times (from 140 to 1120 MPa), and the ultimate strength – by 2.7 times (from 443 to 1175 MPa). As expected, the level of relative elongation significantly decreased (from 68 to 14%). An analysis of the effect of cold rolling on the structure and properties of the Al x CoCrFeNi alloy was performed in [120]. The experimentally recorded increase in the hardness of alloys in comparison with the cast state is due to the manifestation of strain hardening mechanisms. In particular, based on the results obtained by transmission electron microscopy, it has been established that an increase in the strength prop- erties of materials is associated with the formation of numerous structures in the form of nanotwins. With an increase in the degree of plastic deformation, the volume fraction of these defects in the crystal structure increases. In [82], the role of dislocation sliding and twinning processes in the formation of strength proper- ties was shown using the example of the cold rolled CoCrFeNiMn alloy [82]. M.V. Klimova’s thesis work is associated with the study of the effect of deformation-heat treatment on the structure and mechanical properties of high-entropy alloys of the Co-Cr-Fe-Mn-Ni (Al, C) system [21]. The experimentally revealedmicrostructureof theCoCrFeMnNi alloyduring rollingat roomtemperaturedeserves attention. The author of the work identifies three stages of structural transformations associated with the de - gree of plastic deformation of the material: an increase in the dislocations’density ( e = 5-20%); intense defor- mational twinning ( e = 20-60%); formation of shear bands ( e = 60-80%). In the cryogenic temperature range (- 196 °C), the twinning stage shifts to lower values of the degree of deformation. After megaplastic deformation according to the high-pressure torsion scheme (6 GPa), the microhard- ness of the AlCrFeCoNiCu alloy reaches 12 GPa [102]. Under these conditions, all the excess phases are dissolved and a mechano-induced BCC→FCC transformation develops. The subsequent annealing of the alloy leads to the reverse FCC→BCC structure transformation.