Hydrogen uptake and hydride formation in Al$_x$CoCrFeNi high-entropy alloys: First-principles, universal-potential, and experimental study

TL;DR

This study combines experiments, DFT calculations, and a universal interatomic potential to understand hydrogen uptake and hydride formation in Al-Co-Cr-Fe-Ni high-entropy alloys, revealing how composition and ordering influence hydrogen solubility.

Contribution

It introduces a combined experimental and computational approach using a universal potential to analyze hydrogen behavior in complex HEAs, highlighting the impact of aluminum content and ordering.

Findings

Aluminum suppresses hydrogen uptake in HEAs.

Hydrides form in FCC Al$_{0.3}$CoCrFeNi above 3 GPa.

Universal potential accurately reproduces DFT energetics across regimes.

Abstract

Hydrogen uptake in complex multicomponent alloys, including high-entropy alloys (HEAs), governs both hydrogen storage capacity and resistance to hydrogen-induced degradation. We combine high-pressure experiments, density-functional theory (DFT), and a GRACE universal interatomic potential to investigate hydrogen absorption in Al$_{0.3}$CoCrFeNi and Al$_3$CoCrFeNi HEAs. In H$_2$ as a pressure-transmitting medium, the FCC Al$_{0.3}$CoCrFeNi alloy forms hydrides at ambient temperature above 3 GPa, whereas the Al-rich B2 Al$_3$CoCrFeNi alloy shows no evidence of hydride formation even upon heating at pressures up to 50 GPa. Experiments and calculations show that aluminum suppresses hydrogen uptake by increasing solution energies and destabilizing interstitial sites. The universal potential, employed in the calculations and pretrained on large DFT databases, closely reproduces DFT energetics and demonstrates transferability from the dilute limit to the hydride-forming regime. Simulations further disentangle the roles of local ordering, volume changes, composition, and crystal structure. Overall, our results indicate that hydrogen solubility in Al-containing HEAs is governed primarily by composition, with Al-driven B2 ordering as a strong secondary effect.