Abstract
High-pressure torsion (HPT) is widely used as a severe plastic deformation technique to create ultrafine-grained structures with promising mechanical and functional properties. Since 2007, the method has been employed to enhance the hydrogenation kinetics in different Mg-based hydrogen storage materials. Recent studies showed that the method is effective not only for increasing the hydrogenation kinetics but also for improving the hydrogenation activity, for enhancing the air resistivity and more importantly for synthesizing new nanostructured hydrogen storage materials with high densities of lattice defects. This manuscript reviews some major findings on the impact of HPT process on the hydrogen storage performance of different titanium-based and magnesium-based materials.
Highlights
As will be reviewed in this paper, we employed the high-pressure torsion (HPT) method for three main reasons which are of importance in future application of metal hydrides for hydrogen storage: first, production of bulk UFG hydrogen storage materials to facilitate the activation for hydrogenation and improve the air resistivity to deactivation; second, introduction of different kinds of lattice defects such as grain boundaries, amorphous regions, stacking faults and dislocations to enhance the hydrogen storage performance; and third, synthesis of new hydrogen storage materials
It is apparent that while the Mg2Ni sample with large fractions of stacking faults could absorb 2 wt.% of hydrogen within a few minutes, the coarse grained material could not absorb similar amount of hydrogen even after 20 h. These results confirm that the stacking faults produced by HPT processing can be as effective as grain boundaries to enhance the hydrogenation kinetics and activation [34]
The HPT process provides new opportunities to activate hydrogen storage materials, to improve their resistance to deactivation in the air, to enhance their hydrogenation kinetics as well as to synthesize new hydrogen storage materials with unique compositional and microstructural features. All these features are due to the effect of HPT processing on the introduction of lattice defects including the grain boundaries
Summary
This study, together with a few publications on other SPD methods such as equal-channel angular pressing (ECAP) [9–11] and accumulative roll-bonding (ARB) [12–15], reported significant improvement in the hydrogen storage kinetics of Mg-based alloys. As will be reviewed in this paper, we employed the HPT method for three main reasons which are of importance in future application of metal hydrides for hydrogen storage (see some reviews on hydrogen storage materials in [44–46]): first, production of bulk UFG hydrogen storage materials to facilitate the activation for hydrogenation and improve the air resistivity to deactivation; second, introduction of different kinds of lattice defects such as grain boundaries, amorphous regions, stacking faults and dislocations to enhance the hydrogen storage performance; and third, synthesis of new hydrogen storage materials
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