Dislocation mechanisms of acoustic relaxation and plastic deformation of a high-entropy alloy Al0.5CoCrCuFeNi under moderate to deep cooling conditions: Experiment and theory (Review)

The review highlights, analyzes, and summarizes the results of experimental and theoretical study of the general laws and specific features of low-temperature inelastic deformation of a new class of materials, namely, high-entropy alloys (HEAs). The results of a ten-year experimental study of the patterns of acoustic relaxation and the initial stage of plastic deformation of one of the typical representatives of high-entropy alloys—the six-component Al0.5CoCrCuFeNi alloy are described in detail under conditions of moderate (from 300 to 77 K), strong (from 77 to 4.2 K) and deep (from 4.2 to 0.5 K) cooling. In experiments, the temperature dependences of the dynamic moduli of elasticity and internal friction, as well as the main characteristics of the deformation diagrams of polycrystalline samples of the alloy with an fcc atomic structure of grains and a complex morphology of wide grain boundaries, were obtained. The connection between the experimentally recorded features of acoustic and plastic deformation of the alloy and the features of the dynamics and kinetics of elementary dislocation processes in grains and grain boundaries is discussed. At low temperatures, when thermally activated excitation of structural rearrangements in grain boundaries is exponentially weakened, the inelastic deformation of HEAs polycrystals is determined by the nucleation and motion of dislocation-type lattice defects in planes of easy intragrained slip. Analysis and physical interpretation of these processes based on modern dislocation theory made it possible to establish the following: the most important types of defects in the lattice structure of the alloy; types of barriers that prevent the motion of dislocations inside the grains during low-temperature deformation; adequate mechanisms of thermally activated dislocation motion over the barriers at low temperatures; quantitative estimates for the most important characteristics of dislocations and their interaction with barriers.