EBSD microstructural analysis of AB-type TiFe hydrogen storage alloys

Abstract

The microstructural characteristics of three different AB-type TiFe hydrogen storage alloys with Zr or ZrCr2 have been investigated using electron back-scattered diffraction (EBSD) analysis. The major phase of all the as-cast alloys is TiFe phase with the B2 ordered body-centered cubic structure. In addition to the TiFe phase, the TiFeZr and TiFeZrCr alloys have TiFe2 phase with the hexagonal C14 Laves structure and a small amount of Ti2Fe phase with a cubic structure. Based on the EBSD analysis, it is observed that the TiFe2 and Ti2Fe phases exhibit slightly higher kernel average misorientation (KAM) values and smaller grain sizes than the matrix TiFe phase. First hydrogenation (activation) test results of the as-cast alloys indicate that the hydrogenation is easily achieved under 30 bar of hydrogen at room temperature by adding Zr or ZrCr2. This seems to be associated with the presence of the TiFe2 and Ti2Fe phases with higher strain that might act as gateways for hydrogen transport during hydrogenation together with the phase boundaries. The hydrogenation kinetics of the TiFeZr alloy is considerably faster than that of the TiFeZrCr alloy, which might be attributed to the finer grain size of the TiFe2 phase in the TiFeZr alloy.