Additively manufactured high-entropy alloys for hydrogen storage: Predictions

Abstract

This review paper covers an analysis of the empirical calculations, additive manufacturing (AM) and hydrogen storage of refractory high-entropy alloys undertaken to determine the structural compositions, particularly focusing on their applicability in research and experimental settings. The inventors of multi-component high-entropy alloys (HEAs) calculated that trillions of materials could be manufactured from elements in the periodic table, estimating a vast number, N = 10^100, using Stirling's approximation. The significant contribution of semi-empirical parameters such as Gibbs free energy ΔG, enthalpy of mixing ΔH _mix , entropy of mixing ΔS _mix , atomic size difference Δδ, valence electron concentration VEC, and electronegativity difference Δχ are to predict BCC and/or FCC phases in HEAs. Additive manufacturing facilitates the determination of refractory HEAs systems with the most stable solid-solution and single-phase, and their subsequent hydrogen storage capabilities. Hydride materials, especially those from HEAs manufactured by AM as bulk and solid materials, have great potential for H₂ storage, with storage capacities that can be as high as 1.81 wt% of H₂ adsorbed for a ZrTiVCrFeNi system. Furthermore, laser metal deposition (LMD) is the most commonly employed technique for fabricating refractory high entropy alloys, surpassing other methods in usage, thus making it particularly suitable for H₂ storage.

Keywords: Additive manufacturing; Empirical models; High-entropy alloys; Hydrogen storage; Phase prediction; Refractory elements.

Fig. 1

Publication trend of articles with “high-entropy alloy” in orange bars and “high-entropy alloy and phase prediction” in green bars between 2004 and 2023. Data was obtained from the Scopus database.

Fig. 2

Major elements used in the manufacturing of HEAs. Reproduced from Ref. [12].

Fig. 3

Combined impact of ΔH_mix and δ (a), ΔS_mix and δ (b), and the collective influence of all three parameters ΔH_mix, δ, and ΔS_mix (c) on phase stability in equiatomic multi-component alloys. The symbol ○ represents equiatomic amorphous phase forming alloys; ● represents non-equiatomic amorphous phase forming alloys; □ represents solid solution phases and Δ represents intermetallic phases. Reproduced from Ref. [96].

Fig. 4

Influence of Δχ on the HEAs phases, note on the legend: fully closed symbols for sole FCC phases; fully open symbols for sole BCC phase; half closed symbols for mixes FCC and BCC phases. Reproduced from Ref. [101].

Fig. 5

Valence electron concentration in terms of the i-th component concentration C_i for the HEA systems (a) (AlCoCrFeNi)_100-xNi_x and the (b) (CoCrCuFeNi)_100-xMo_x. Reproduced from Ref. [102].

Fig. 6

Parameter values of Ω vs. δ for various HEAs. Reproduced from Ref. [80].

Fig. 7

Potential energy difference in the migration of a Ni atom, the mean difference in potential energy before (blue line) and after (red line) migration. Reproduced from Ref. [112].

Fig. 8

Representation of the working principle of the three metal additive manufacturing categories with main terminology. (a) Schematics of an LMD set-up. Reproduced from Ref. [130]. (b) Schematic of SLM, labels; 1 = powder layer coater, 2 = laser beam, 3 = print bed. Reproduced from Ref. [131]. (c) Schematic of EBM, labels; 1 = electron gun, 2 = lens system, 3 = deflection lens, 4 = powder cassettes with feedstock, 5 = roller or rake, 6 = building component, 7 = print bed. Reproduced from Ref. [132].

Fig. 9

Schematic illustration of an in-situ reaction of the Mn elemental powder to form MnO and Mn₂O₃. Reproduced from Ref. [139].

Fig. 10

Phase maps of the top part and the bottom part of the AℓCoCrFeNi manufactured by a selective EBM process. Reproduced from Ref. [154].

Fig. 11

Depiction of hydrogen uptake and release in high-entropy alloys and their respective hydrides. Reproduced from Ref. [170].

Fig. 12

Pressure-composition temperature absorption and desorption curves of LaNiFeVMn at 35 °C, (a) before activation & (b) after activation. Reproduced from Ref. [152].

Fig. 13

(a) Pressure-composition temperature absorption and desorption curves of ZrTiVCrFeNi at 50 °C. Reproduced from Ref. [2]. (b) Pressure-composition temperature absorption and desorption curves of TiZrCrMnFeNi at 32 °C. Reproduced from Ref. [180].