Reversible hydrogen absorption/desorption and related phase transformations in a Ti3Al alloy with the stoichiometry composition Original Research Article

Reversible hydrogen absorption/desorption was observed in an α2-Ti3Al alloy. Two different γ hydrides, i.e. γH1 and γH2, were identified. γH2 has a higher hydrogen content than γH1. The βH-γH1 phase transformation is reversible and the observed reversible hydrogen absorption/desorption is due to this reversible phase transformation. Once alloys absorb hydrogen enough to form γH2, no reverse γH→βH transformation occurs and thus no desorption plateau is observed. The γH2 phase is formed when hydriding is made quickly at high hydrogen pressures and/or lower temperatures. Degradation of the reverse γH→βH transformation also occurs when pulverized specimens are hydrogenated. The structure of the metal lattice of βH is determined. Many twins exist in βH. The mechanism of the reversible βH-γH1 transformation in the Ti3Al alloy was discussed in terms of the lattice deformation and ordering of hydrogen atoms required for the βH-γH1 transformation.