Mechanical Properties of HfxNbTaTiZr Refractory High-Entropy Alloys via Molecular Dynamics

Abstract

Refractory high‑entropy alloys (RHEAs) combine outstanding high‑temperature strength with broad compositional tunability, yet they suffer from limited ductility at room temperature and decreased thermal stability. In this study, we use molecular-dynamic simulations to probe Hf_xNbTaTiZr (x = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75) 2.00) over 77-900 K. Uniaxial tension and nanoindentation reveal that raising Hf content expands the lattice (3.382→ 3.468 Å) and, at 900 K, cuts the Young's modulus from 154.5 to 88.2 GPa and ultimate strength from 1,000 to 450 MPa while hardness drops by up to 47 %; intermediate Hf levels (x = 0.50~1.25) retain low-temperature hardness. We identify the atomic-scale mechanisms—solid‑solution weakening under thermal activation and phase‑structure evolution—that govern these trends. These insights pave the way for designing RHEAs with an optimal balance of strength, ductility, and high‑temperature stability for extreme‑service applications.