Effect of heat treatment on microstructure and thermal stability of Ti19Hf4V40Mn35Cr2 hydrogen storage alloy

In order to improve the hydrogen storage capacity, Ti19Hf4V40Mn35Cr2 alloy was prepared with low-temperature heat treatment (973 K, 2 h/8 h/72 h, water quenching). Microstructure, hydrogen storage properties and hydrogen absorption/ desorption mechanism have been investigated. The results show that ascast and heat treated Ti19Hf4V40Mn35Cr2 alloys consist of BCC phase, C14 Laves phase and Hf-rich phase. Large amounts of equiaxed dendrite BCC phase and eutectic structure (BCC phase + C14 Laves phase) were formed after heat treatment. The hydrogen storage capacity at the room temperature comes the highest up to 2.34 wt% for holding 72 h, which is 12% points higher than the as-cast alloy. The activation energy of as cast Ti19Hf4V40Mn35Cr2 alloy was about 83.30 kJ/mol, and the activation energies of heat treated alloys decreased to 66.26 kJ/mol, which is caused by the decreasing stability of hydride after heat treatment. (c) 2022 Elsevier B.V. All rights reserved.