Effect of particle size, pressure and temperature on the activation process of hydrogen absorption in TiVZrHfNb high entropy alloy

Abstract

The effect of particle size, pressure and temperature on the first hydrogenation of TiVZrHfNb high entropy alloy were investigated. Three particle size ranges were selected: less than 0.5 mm, between 0.5 mm and 1 mm and between 1 mm and 2 mm. The hydrogen pressure applied during the first hydrogenation was 1 bar, 2 and 20 bars. The temperature of first hydrogenation was varied from 100 °C to 400 °C. It was found that the particle size plays a role in the activation; smaller particle size having faster kinetics. Under 2 bars and 20 bars of hydrogen pressure, the activation curves have the same features. The activation is strongly dependent on the temperature: higher temperature drastically reduces the incubation period. The important parameter for the activation is the temperature rather than the particle size. It was also found that the activation process obeys an Arrhenius relationship. Upon hydrogenation, the BCC phase is transformed to a BCT phase. Also, an amorphous phase seems to be formed. This formation depends on the hydrogenation temperature and particle size.