Design and mechanosynthesis of Low-Weight High-Entropy Alloys with hydrogen storage potential properties

This investigation allows designed MgAl-based Low-Weight High-Entropy Alloys (LWHEAs) with a BCC-type structure, using a MgAlTi(X)Ni system where X = Fe, Cr and Co, with hydrogen storage potential properties. The BBC-type alloys were designed considering empiric thermodynamic parameters and obtained by high-energy ball-milling. The structure, morphology, thermal stability and hydrogen sorption properties were studied. Also, the influence of Valence Electron Concentration (VEC_mix) and Electronegativity difference (Δχ_mix) parameters on the hydrogen storage capacity of alloys was evaluated. The formation of the equiatomic MgAlTiFeNi, MgAlTiCrNi and MgAlTiCoNi BCC-type LWHEAs with densities between 4.3 ≤ ρ ≥ 4.6 g cm⁻³ was obtained at 8 h of milling. Alloyed powders show a homogeneous elemental distribution with heterogeneous particles of different sizes and a surface area of ∼ 2 g cm⁻². Under high-temperature conditions, the LWHEAs structure changes from BCC to B2. The MgAlTiCoNi alloy presented a maximum hydrogen storage capacity of 2.1% weight H₂ at 473 K and 1 MPa. The hydrogen storage depended on VEC_mix and Δχ_mix parameters in LWHEAs with the same mixing Entropy.