Dehydrogenation thermodynamics of Hf1-Ti NbVZr (x = 0, 0.25, 0.5, 0.75 and 1) high entropy alloys

The effect of the partial substitution of hafnium with titanium on the thermodynamic parameters of Hf 1- x Ti x NbVZr HEA was investigated (from x = 0 to 1 by step of 0.25). For each composition, a pressure–concentration isotherm (PCI) was registered at 573, 598, 623 and 648 K. The PCT curves revealed an increase in plateau pressure with increasing Ti content. Entropy (ΔS) and enthalpy (ΔH) values were deducted from the Van’t Hoff plots of the PCT curves. With Ti content increasing from 0 to 1 in Hf 1- x Ti x NbVZr, the enthalpy values ranged from -22 to -93 kJ/mol H 2 , while the entropy values ranged from 29 to 152 J/K.mol H 2 . A linear correlation was observed when plotting ΔS as a function of ΔH, indicating a potential enthalpy–entropy compensation effect. Quality factor analysis did not provide statistically significant support for this relationship, indicating that a statistical origin cannot be excluded with 95% confidence. • PCI curves show plateau pressure rises as Ti content increases in Hf₁₋ₓTiₓNbVZr HEA. • ΔH shifts from -22 to -93 kJ/mol H₂; ΔS ranges from 29 to 152 J/K·mol H₂ as Ti increases. • A linear ΔS–ΔH correlation suggests an enthalpy–entropy compensation effect. • Quality factor analysis shows no significant proof; statistical origin not ruled out.