Formation of eutectic and hydrogen absorption/ desorption behavior of heat-treated Ti19Hf4V40Mn35Cr2 alloys

The effect of high-temperature heat treatment (1673 K, 1min/5min/30min, water quenching) on the microstructure and hydriding/dehydriding properties of Ti19Hf4V40Mn35Cr2 alloys was studied. Both the proportion and lattice contraction of BCC phases increased after heat treatment. The eutectic (BCC phase + C14 Laves phase) structure was formed under different heat treatment conditions. Ti19Hf4V40Mn35Cr2 treated at 293 K for 1 min had the highest hydrogen storage capacity (2.23 wt%) and the fastest absorption rate. This was because of the easy and fast diffusion of H atoms. The dehydriding enthalpy (ΔH) of the as-cast alloys was 41.70 kJ/mol H2, which was higher than 33.62 kJ/mol H2 of heat-treated alloys. The reason was the decrease in hydride stability.