Effect of heat treatment on microstructural evolution and hydrogen storage performance of as-milled Ti5+xV35(CrMnFe)60-x (x=0, 10, 20, 30) high-entropy alloys

The increasing attention on high-entropy alloys (HEAs) stems from their distinctive properties, with particular emphasis on the remarkable hydrogen storage capacity of body-centered cubic (BCC) structured HEAs. This study investigates the microstructural evolution, thermal stability, and hydrogen storage behavior of as-milled Ti5+xV35(CrMnFe)60-x (x = 0,10,20,30) high-entropy alloys (HEAs) before and after heat treatment (HT). The microstructural characterization of the ball-milled HEAs reveals the presence of primary BCC and minor amounts of C14 Laves, with the proportion of C14 Laves gradually increasing with increasing Ti content. The hydrogen absorption capacity of the x = 30 alloy at room temperature is measured at 1.21 wt%, with a desorption capacity of 0.336 wt%. The phase stability of the alloys after HT depends on the Ti content, with the microstructure maintaining a nanoscale even after HT at 900 °C. The reduction in the BCC lattice constant after HT (x = 30) and synergistic effects among different phases (Laves and FCC), the hydrogen storage capacity decreases to 1.10 wt%, while desorption capacity slightly increases to 0.46 wt%. These findings elucidate the influence of mechanical alloying and HT on the microstructure and hydrogen storage performance of high-entropy alloys.