Citation: Mahmoud, E.R.I.; Shaharoun, A.; Gepreel, M.A.; Ebied, S. Phase Prediction, Microstructure and Mechanical Properties of Fe–Mn–Ni–Cr–Al–Si High Entropy Alloys. Metals 2022, 12, 1164. https://doi.org/10.3390/ met12071164 Academic Editors: Carlos Alexandre Dos Santos and Eleani Maria Da Costa Received: 8 June 2022 Accepted: 4 July 2022 Published: 8 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Phase Prediction, Microstructure and Mechanical Properties of Fe–Mn–Ni–Cr–Al–Si High Entropy Alloys Essam R. I. Mahmoud 1, * , Awaluddin Shaharoun 1 , Mohamed A. Gepreel 2 and Saad Ebied 3 1 Department of Mechanical Engineering, Islamic University of Madinah, Madinah 42351, Saudi Arabia; prof.awaluddin@gmail.com 2 Materials Science and Engineering Department, Egypt-Japan University of Science and Technology, New Borg El-Arab 16448, Egypt; mohamed.gepreel@ejust.edu.eg 3 Department of Production Engineering and Mechanical Design, Faculty of Engineering, Tanta University, Tanta 31527, Egypt; saad_ebied@f-eng.tanta.edu.eg * Correspondence: essamibrahim2@yahoo.com; Tel.: +966-543876061 Abstract: The selection of high-entropy alloys (HEAs), which are relatively lightweight and have unique mechanical properties, remains a substantial challenge. In this study, six new HEAs were designed from the relatively low-cost Fe–Mn–Ni–Cr–Al–Si system using Thermo-Calc software, and then manufactured using a casting process. The effects of the atomic ratio of the alloying elements on the microstructures and mechanical properties of these alloys in the as-cast condition were systematically investigated. Brittle body-centered cubic BCC/B2 and silicide phases were found in relatively large amounts in the form of dendritic structure within large equiaxed grains with fine needle-shaped phases in the Fe 30 Mn 15 Ni 20 Cr 15 Al 10 Si 10 and Fe 35 Mn 15 Ni 20 Cr 15 Al 10 Si 5 alloys, in addition to the face-centered cubic (FCC) phase. When the contents of Mn and Ni were increased in the Fe 35 Mn 25 Ni 15 Cr 15 Al 5 Si 5 and Fe 35 Mn 20 Ni 20 Cr 15 Al 5 Si 5 alloys, the amounts of brittle phases were reduced; however, the ductile FCC phase is not significant. The FCC phase amount, which appeared as a honeycombed structure, was more than enough when the Si content was decreased to 3%. Broad relationships between the chemical composition of the alloys, especially the Si content, and the hardness and compression properties’ measurements were established. As the Si content decreased, both the hardness and compression properties of the resulting alloy also decreased. The experimental observation of the six HEAs matched the equilibrium phases predicted by the Thermo-Calc calculations. Keywords: high-entropy alloy; thermo-calc calculation; casting; microstructure analysis; hardness measurements 1. Introduction High-entropy alloys (HEAs) have attracted many researchers’ attention since 2004, after Jien-Wei Yeh and Brian Cantor [1,2] achieved good results from them in their work. High-entropy alloys (HEAs) can be defined as multi-metallic materials, containing four or more basic alloying elements in equal atomic percentages (at.%) or near-equiatomic proportions [3,4]. The atomic portion of each element is often in excess of 5 at.%. This design philosophy was initially aimed at stabilizing the massive solid solutions of a single phase over high configurational entropy. These newly designed alloys have exceptional mechanical properties, which may vary entirely from their basic elements [5–8]. HEAs are a favored approach for the production of high-performance alloys with improved mechanical toughness and strength, higher thermal stability, enhanced oxidation, soft magnetic properties, and corrosion resistance [9–12]. In addition, several HEAs have shown high resistance to irradiation, exhibiting lower irradiation-stimulated segregation and reduced density of dislocation loops, compared to ordinary alloys [13,14], and pos- sessing self-healing properties [15,16]. These unique properties position them as the first Metals 2022, 12, 1164. https://doi.org/10.3390/met12071164 https://www.mdpi.com/journal/metals