| Summary: | Refractory high-entropy alloys (RHEAs) Al<sub>20+x</sub>Cr<sub>20-x</sub>Mo<sub>20-y</sub>Ti<sub>20</sub>V<sub>20+y</sub> ((x, y) = (0, 0), (0, 10), and (10, 15)) were computationally studied to obtain a low density and a better mechanical property. The density functional theory (DFT) method was employed to compute the structural and mechanical properties of the alloys, based on a large unit cell model of randomly distributed elements. Debye–Grüneisen theory was used to study the thermal properties of Al<sub>20+x</sub>Cr<sub>20-x</sub>Mo<sub>20-y</sub>Ti<sub>20</sub>V<sub>20+y</sub>. The phase diagram calculation shows that all three RHEAs have a single body-centered cubic (BCC) structure at high temperatures ranging from 1000 K to 2000 K. The RHEA Al<sub>30</sub>Cr<sub>10</sub>Mo<sub>5</sub>Ti<sub>20</sub>V<sub>35</sub> has shown a low density of 5.16 g/cm<sup>3</sup> and a hardness of 5.56 GPa. The studied RHEAs could be potential candidates for high-temperature application materials where high hardness, ductility, and low density are required.
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