Composition dependence of hydrogen absorbing properties in melt quenched and annealed TiMn2 based alloys

Abstract

We have investigated the hydrogen absorbing properties of binary TiMn2 based alloys with the compositions ranging from Ti–56.4 to 66.8at.% Mn, which were prepared by melt quenching and subsequent annealing, as well as arc melting and subsequent annealing for comparison. All the alloys are composed of TiMn2 and TiMn phases, where the volume fraction of the TiMn2 Laves phase increases with increasing Mn content. In the annealed alloys with Ti–56.4 to 59.4at.% Mn, the Mn content of the TiMn2 phase is about 60at.%; whereas in the alloys beyond 59.4at.%, it increases with increasing the Mn content of the alloys. Correspondingly, the hydrogen absorbing capacity of the alloys increases with increasing the Mn content up to 59.4at.%, but rapidly decreases with a further increase of the Mn content. These observations suggest that the alloy composition exhibiting the maximum hydrogen absorbing capacity is determined by a compromise of a high volume fraction and a low Mn content of the TiMn2 phase. In addition, we found that rapidly solidified alloys exhibited poor hydrogenation behavior. Therefore, it is concluded that the hydrogen absorbing capacity of the TiMn2 based alloys is mainly governed by the composition of alloy and probably by the atomic arrangement of excess Ti atoms within the TiMn2 phase.