Effect of substitutional elements on the hydrogen absorption-desorption properties of Ti₃Al compounds

Ternary elements M were substituted into Ti₃Al with the aim of reducing the hydrogen desorption temperature of Ti₃AlH_x. On hydrogenation at room temperature, three different states, i.e. amorphous, bcc and C14 Laves phases, were obtained depending on the alloying elements and their amount. The amorphous hydrides formed in the alloys substituted with Zr or Hf showed a high hydrogen capacity and high hydrogen desorption temperature. In the case of the bcc hydrides, formed in the alloys substituted with V or Cr, the hydrogen capacity was largely reduced, but the hydrogen desorption temperature was unchanged or increased. Therefore, V and Cr are the worst substitutional elements to Ti₃Al. On the other hand, the hydrides having C14 Laves structure formed in the alloys substituted with Mn, Co or Ni showed a reduced hydrogen desorption temperature, although the hydrogen capacity was decreased to same extent. From the present work, Mn, Co and Ni are considered to be effective elements for improvement of the hydrogen absorption-desorption properties of Ti₃Al.