Effect of Mo on Phase Stability and Properties in FeMnNiCo High-Entropy Alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2022-05, Vol.53 (5), p.1749-1760
• Main Authors: Cichocki, Kamil, Bała, Piotr, Kozieł, Tomasz, Cios, Grzegorz, Schell, Norbert, Muszka, Krzysztof
• Format: Article
• Language: English
• Subjects: Alloying; Alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Compression tests; Density functional theory; Electric arc melting; Enthalpy; High entropy alloys; Hot rolling; Intermetallic phases; Materials Science; Mechanical properties; Metallic Materials; Microstructural analysis; Microstructure; Modelling; Molybdenum; Nanotechnology; Original Research Article; Phase stability; Solid solutions; Structural Materials; Surfaces and Interfaces; Thin Films; X-ray diffraction
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-022-06629-x

The goal of this research was to propose a combined modeling approach to design a stable alloy based on the FeMnNiCoMo system. First, phase stability calculations were made using valence electron calculations (VEC) and density functional theory (DFT) methods. The effect of Mo alloying in the FeMnNiCo system was investigated by calculating characteristics of solid solution combined with the different methods. The DFT method was used to obtain formation enthalpy in the (FeMnNiCo) 100– x Mo x system for stable face-centered-cubic (fcc) and body-centered-cubic (bcc) structures. The calculations were made for Mo contents from 0 to 20 at. pct. Classic thermodynamic calculations, such as mixing enthalpy, configurational entropy, or valence electron concentration (VEC), were used. Based on these calculations, the proposed alloy should be characterized by fcc structure in the entire considered Mo content, without occurrence of any intermetallic phases. Subsequently, three alloys with 0, 5, and 10 at. pct Mo were produced using arc melting and were further investigated. Alloys were homogenized and then hot rolled into flat bars. Microstructural analysis was performed using as-cast, after-homogenization, and hot-rolled specimens. The microstructures were characterized by means of scanning electron microscopy–energy-dispersive spectroscopy (EDS) analysis. Mechanical properties were evaluated using tensile and compression tests. In addition, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were also conducted. The results from EDS and XRD showed the occurrence of intermetallic phases in investigated alloys, as phase with Fm 3- m space group and in µ phase in (FeMnNiCo) 90 Mo 10 alloy. Based on the comparison of the experimental and calculated results, conclusions regarding the structural changes with Mo content were drawn and the validity of the proposed modeling approach was tested and discussed.