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

The goal of this research was to propose a combined modeling approach to design a stable alloybased on the FeMnNiCoMo system. First, phase stability calculations were made using valenceelectron calculations (VEC) and density functional theory (DFT) methods. The effect of Moalloying in the FeMnNiCo system was investigated by calculating characteristics of solidsolution combined with the different methods. The DFT method was used to obtain formationenthalpy 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, orvalence electron concentration (VEC), were used. Based on these calculations, the proposedalloy should be characterized by fcc structure in the entire considered Mo content, withoutoccurrence of any intermetallic phases. Subsequently, three alloys with 0, 5, and 10 at. pct Mowere produced using arc melting and were further investigated. Alloys were homogenized andthen hot rolled into flat bars. Microstructural analysis was performed using as-cast,after-homogenization, and hot-rolled specimens. The microstructures were characterized bymeans of scanning electron microscopy–energy-dispersive spectroscopy (EDS) analysis.Mechanical properties were evaluated using tensile and compression tests. In addition, X-raydiffraction (XRD) and differential scanning calorimetry (DSC) analyses were also conducted.The results from EDS and XRD showed the occurrence of intermetallic phases in investigatedalloys, as phase with Fm3-m space group and in l phase in (FeMnNiCo)$_{90}$Mo$_{10}$ alloy. Based onthe comparison of the experimental and calculated results, conclusions regarding the structuralchanges with Mo content were drawn and the validity of the proposed modeling approach wastested and discussed