Study of the Change in the Structure and Properties of High-Entropic Alloys during Thermal and Thermomechanical Processing

Abstract

Multicomponent alloys without a base element, also known as highly entropic alloys (HEAs), are of great interest for research. The microstructure of the Fe 20 Ni 20 Co 20 Cu 20 Al 20 alloy in a cast, annealed, and deformed state, as well as its mechanical properties and hot deformation ability, is investigated in this article. This alloy is a typical representative of the high-entropy alloy family. Samples are melted in a vacuum induction furnace in an argon atmosphere and then cast into a copper mold. Differential scanning calorimetry results are used to determine the solidus temperature. The homogenization annealing of cast samples is carried out in a high-temperature furnace in air. The microstructure of the alloy is studied by scanning electron microscopy and X-ray diffraction. X-ray microanalysis using X-ray energy dispersive spectroscopy is used to determine the chemical composition of the phases. It is shown that crystallization results in the formation of three solid solutions with one bcc and two fcc crystalline structures. The mechanical properties are investigated under uniaxial compression. Hardness is also measured. The deformation tests are carried out on a DIL805A/D quenching-deformation dilatometer and a Gleeble System 3800 complex for physical modeling and dynamic thermomechanical testing at temperatures of 900-1100°С and strain rates of 0.01-1.0 s -1 for a true degree of deformation of up to 1. Optimum modes of homogenization annealing for the typical representative of HEAs and optimal deformation modes are selected to obtain high mechanical properties.

The Study of Structural Changes in Homogenized High-Entropy Alloys

“…The formation of the third phase and, most importantly, the transition of the disordered bcc A2 lattice to B2 are probably the reason for the higher hardness of HEA 4 in the annealed state. Three solid solution phases (fcc1, fcc2, bcc) were also found in HEA 1 [25].…”

“…The hardness of HEA 2 and HEA 4 is much lower than that of HEA 1 (395 HV) [25]. The high hardness of HEA 3 is determined by the presence of chromium, possibly also due to the ordering of B2-type phases or the sigma phase [27].…”

“…The composition of the alloys is given in Table 1. The previously investigated alloy HEA 1 is given for comparison [25].…”