Hydrogenation behavior of high-entropy alloy TiZrVNbTa: Thermochemical analysis

For hydride-forming alloys, the thermochemical parameters of interaction with hydrogen are of particular fundamental and applied interest. In this work, Tian-Calvet heat-flow calorimetry was used in combination with volumetric and structural studies to identify and attribute the hydrogenation stages of the high-entropy equiatomic alloy TiZrVNbTa with body-centered cubic (BCC) structure. To eliminate the high-temperature activation, a thin-layer palladium coating was applied to the alloy surface. It has been established that the hydrogenation proceeds as a three-stage process with the sequential formation of a solid solution of hydrogen, a tetragonally distorted monohydride and a dihydride with a face-centered cubic lattice. While the whole process is characterized by the enthalpy ΔH= −103 kJ/mol H 2 , the first stage is the most exothermic, and the heat of hydrogen dissolution in the metal lattice at low concentrations reaches 180 kJ/mol H 2 . The obtained results confirm the fruitfulness of the calorimetric approach to the study of processes in metal-hydrogen systems and make a significant contribution to the formation of ideas about phase transformations occurring during the interaction of HEA S with hydrogen and the influence of surface modification on them. • Hydrogenation of TiZrVNbTa HEA was studied using Tian-Calvet heat flux calorimetry • Thin coating with Pd was used to eliminate high-temperature activation • Three stages of hydrogenation were identified and attributed to phase transformation • Formation of BCC H-solid solution is the most exothermic stage with ΔH=-180 kJ/mol H 2