Investigation on the activation mechanism of hydrogen absorption in TiZrNbTa high entropy alloy

In this study the activation behavior of hydrogen absorption in a TiZrNbTa high-entropy alloy (HEA) has been investigated. Results showed that the hydrogen absorption temperature of the TiZrNbTa HEA were significantly decreased from 715 K to room temperature, and the hydrogen absorption kinetics were also improved greatly after activation. The X-ray photoelectron tests showed that, after activation, almost all the oxides at the surface of the TiZrNbTa HEA were reduced to suboxides and sub-hydroxides after activation, but only parts of oxides at the surface of pure metals were reduced, in the form of suboxides. Based on these results, a two-step mechanism for the activation of TiZrNbTa HEA was proposed. The positron annihilation lifetime analysis showed that both the size and concentration of vacancy clusters increased significantly in the TiZrNbTa HEA after activation. It could be responsible for the improvement of hydrogen absorption kinetics in TiZrNbTa HEA.