HYDROGEN ABSORPTION AND MICROSTRUCTURE IN BCC ALLOYS WITH C-14-TYPE LAVES PHASE

Recently, the AB(2)-type Laves phase alloys and the BCC solid solution alloys have been investigated as next generation hydrogen-absorbing alloys with the high capacity. We propose the new concept of alloy design named ''Laves phase-related BCC solid solution'' in this work. First, the multi-phase alloy Zr0.5Ti0.5VMn consisting of the BCC solid solution phase and the C14-type Laves phase is designed as a variation of the ''Laves phase-related BCC solid solution''. Secondly, the multi-phase alloy Zr63Mn37 consisting of the alpha-Zr H.C.P.solid solution phase and the ZrMn2 C14-type Laves phase is designed for the control experiments. End members of these alloys such as ZrMn2, Zr93Mn7 and TiV2 are prepared for calculation of the composite law of hydrogen storage capacity. In the pressure-composition isotherm, the composite law of hydrogen storage capacity is successful in the zirconium and manganese binary alloy Zr63Mn37 at each equilibrium pressure between the alpha-Zr HCP solid solution phase and the ZrMn2 Laves phase. This law, however, does not explain the capacity of the quaternary multi-phase alloy Zr0.5Ti0.5VMn under the simple assumption that this ahoy consists of the Ti-V BCC solid solution and the ZrMn2 C14-type Laves phase. In order to understnad this disagreement, the relations of the Ti-V BCC solid solution phase and the ZrMn2 C14-type Laves phase are discussed by investigating the morphology and analyzing the crystal structure of the multi-phase alloy. The morphology is investigated by optical microscopy, scanning electron microscopy and transmission electron microscopy, and the crystal structure is analyzed by X-ray Rietveld refinement and selected area electron diffraction. These metallographical approaches in this work will become the first step of improvement for the hydrogen-absorbing property by the control of the microstructure.