Impact of severe plastic deformation on microstructure and hydrogen storage of titanium-iron-manganese intermetallics

TiFe1-xMnx intermetallics (x=0, 0.15 and 0.3) were severely deformed by high-pressure torsion (HPT) to enhance their activation and air resistivity for hydrogenation. While the as-cast ingots hardly absorbed hydrogen (TiFe0.7Mn0.3 exhibited slow activation after an incubation period), the HPT-processed samples absorbed hydrogen quickly at room temperature even after air exposure. The improvement of hydrogen storage performance was due to the formation of lattice defects and amorphous regions, which act as channels for hydrogen diffusion. Rietveld analyses and first-principles calculations showed that Mn addition expands the lattice and reduces the hydride formation energy, and thus decreases the hydrogenation/activation pressure. [Display omitted]