The promising results obtained in the research of high-entropy alloys are increasingly encouraging new configurations of these alloys. Our research was conducted on the high-entropy CoCrFeMoNi alloy and the Ti-doped CoCrFeMoNi alloy. Electrochemical impedance spectroscopy (EIS) measurements were performed on samples with and without Ti-doped CoCrFeMoNi high-entropy alloys in order to evaluate the influence of voltage on their behavior in a simulated aggressive environment. The impedance spectra were measured between −1.0 and +0.8 V vs. SCE at various potential levels. Using an electrical equivalent circuit to match the experimental data, the impedance spectra were analyzed. The corresponding circuit that successfully fits the spectra has two time constants: the first one is for the attributes of the compact passive layer and the second one is for the features of the porous passive layer. The results show that doping CoCrFeMoNi alloy with 0.36 at.% Ti reduces the alloy’s ability to resist corrosion, as the alloy can react more quickly to the surrounding environment and cause a decrease in the corrosion resistance of the alloy.
The design principle of high-entropy alloys is to mix many chemical elements in equal or nearly equal proportions to create new alloys with unique and special properties such as high strength, ductility and corrosion resistance. Some properties of high-entropy alloys can be adjusted via introducing new doping elements, which are selected according to working conditions. The high-entropy alloy CoCrFeMoNi was examined to determine the impact of Ti doping on its micro-structure, microhardness and elastic modulus. Microstructure analysis revealed a core structure consisting of both face-centered cubic (FCC) and body-centered cubic (BCC) phases, along with the formation of a Laves phase. The addition of Ti made the alloy grains finer and reduced the Mo concentration difference between the interdendritic and dendritic regions. As a result of Ti doping, the microhardness of the alloy increased from 369 HV 0.2 to 451 HV 0.2. Ti doping produced a doubling of the breaking strength value, although no significant changes were observed in the elastic modulus of the CoCrFeMoNi alloy.
The aim of the paper is to study the Zr addition effect on the mechanical properties and corrosion behavior of a high-entropy alloy from the CoCrFeMoNi system. This alloy was designed to be used for components in the geothermal industry that are exposed to high temperature and corrosion. Two alloys, one Zr-free (named Sample 1) and another one doped with 0.71 wt.% Zr (named Sample 2), were obtained in a vacuum arc remelting equipment from high-purity granular raw materials. Microstructural characterization and quantitative analysis by SEM and EDS were performed. The Young modulus values for the experimental alloys were calculated on the basis of a three-point bending test. Corrosion behavior was estimated by linear polarization test and by electrochemical impedance spectroscopy. The addition of Zr resulted in a decrease in the value of the Young modulus but also in a decrease in corrosion resistance. The beneficial effect of Zr on the microstructure was the grain refinement, and this ensured a good deoxidation of the alloy.
Due to the optimistic outcomes of the research on high-entropy alloys, new designs of these alloys are being encouraged. We studied the high-entropy CoCrFeMoNi alloy and the CoCrFeMoNi alloy doped with Zr. In order to choose the best electrical equivalent circuit for the prediction of the behavior of these high-entropy alloys at various potentials in artificial seawater, electrochemical impedance spectroscopy (EIS) measurements were conducted on samples with and without Zr-doped CoCrFeMoNi. At various potential levels, the impedance spectra were measured between −1.0 and +0.8 V vs. SCE. The study consists of a preliminary section with microstructure by metallography, open-circuit potential, and linear polarization curves by direct-current tests followed by visual analysis of the impedance spectra, and, finally, the selection of an equivalent electrical circuit model to fit the experimental data. By leveraging the advantages of EIS analysis, the information is essential for materials development, corrosion-mitigation strategies, and the successful implementation of these alloys in practical applications. It is important to note that selecting an equivalent circuit is often an iterative and subjective process, as it involves a balance between model complexity and the ability to accurately represent the system’s behavior.
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