Construction of FeCrVTiMo_x high-entropy alloys with enhanced mechanical properties based on electronegativity difference regulation strategy

The development of high-entropy alloys (HEAs) as coating materials for protecting cutting tools remains a big challenge due to the diversity of their compositions and structures. In this work, we demonstrated an electronegativity regulation strategy to improve the mechanical properties of FeCrVTiMo_x HEAs coatings by introducing the high-electronegativity Mo element, which has been confirmed to be effective both in theoretical calculations and experimental studies. Thermodynamic analysis and the first-principles calculations predicted that FeCrVTiMo_x could readily form a single solid solution with a body-centered cubic (BCC) phase, and the electronegativity difference with increased Mo content showed a linear correlation for the improved mechanical properties of HEAs. The FeCrVTiMo_x HEA coatings synthesized using the laser cladding technique exhibited the increased Young's modulus from 227.8 GPa to 251.6 GPa, the increased Vickers hardness from 2.15 GPa to 8.19 GPa, and in the decreased frictional wear weight loss from 1.14 mg to 0.18 mg, supporting the predictions. The microscopic mechanism of solid solution strengthening of Mo elements was analyzed by Density of states (DOS) and electron localization function (ELF). The d-orbital electron of each metal atom hybridizes with one another, leading to that Mo element with high electronegativity can attract and localize electrons to form covalent bonds. The larger electronegativity difference is, the more covalent bonds can be formed, in turn enhancing the mechanical properties of HEAs.