Structural investigation and hydrogenation properties of TiZrXMnFeNi (X = Cr, Mo, and W) high entropy alloys

Abstract

In this study, we design and synthesize three high entropy alloys with a composition of TiZrXMnFeNi (X = Cr, Mo, and W), using semi-empirical thermodynamic parameters. These alloys have the same value of VEC= 6.49 and mixing entropy of 14.89 J·K−1·mol−1. The main crystal structure in all samples is C14 hexagonal Laves phase, with Mo and W-rich precipitation in TiZrMoMnFeNi and TiZrWMnFeNi, respectively. Thermodynamic properties of hydrogen absorption/desorption, the effect of temperature and applied hydrogen pressure, cyclic stability up to 50 cycles, and calculation of apparent activation energy have been investigated in detail. By substituting Cr with Mo and, W atoms in the alloy composition, the hydrogen absorption capacity decreases (from 1.4 to 1.2, and 0.8 wt% respectively, at 268 K), and the hydrogen absorption rate increases markedly. Additionally, the rate-controlling step of hydrogen absorption changes from diffusion to nucleation and growth. The results indicate that the substitution of heavier atom in this composition and thus increasing the Ω parameter leads to the formation of preferential nucleation sites and facilitate hydrogen absorption.