Observation of short-range order in refractory high-entropy alloys from atomic-positions deviation using STEM and atomistic simulations

Chemical short-range order (SRO) has an intriguing relationship with the mechanical properties in solid-solution alloys. Here, we report experimentally observed SRO and atomic-level quantification of lattice distortions in the NbTaTiV and NbTaTiVZr refractory high-entropy alloys (RHEA), using atomic-resolution scanning transmission electron microscopy (STEM) coupled with atomistic simulations. Combination of atomic position and intensity analysis estimate the relationship between atomic bonds and SRO, indicating the bonding preference of Ta-V, Ti-V, Ti-Zr, and Nb-Ta. The non-randomness of interatomic distances and significant deviation in the predicted value of lattice distortions are associated with a significant SRO in NbTaTiVZr RHEA. Monte Carlo simulations with both first-principles cluster expansion Hamiltonians and machine-learning interatomic potentials verify the existence of SRO and reveal the underlying origin for the bonding preference trends in NbTaTiVZr. It can be attributed to the large electronegativity difference and moderate atomic-size mismatch between Zr and other atoms.