Hydrogen-induced amorphization of YNi2 enhanced by reactive mechanical grinding

Keiji Funaki, Shin Ichi Orimo, Hironobu Fujii

Research output: Contribution to journalArticlepeer-review


The C15 Laves phase YNi2, which becomes amorphous YNi2Hx by hydrogenation, was mechanically ground under various hydrogen partial pressures up to 1.0 MPa to investigate the effect of the mechanical grinding (MG) on the hydrogen-induced amorphization (HIA) processes. Furthermore, the phase separation processes during dehydriding reaction were also examined. The results obtained are summarized as follows. Under the initial hydrogen pressure of 1.0 MPa, a single phase of amorphous YNi2Hx is observed by grinding only for 180 min, while such an amorphization can hardly occur even after hydrogenation for 10080 min without grinding. However the thermal stabilities of the amorphous phase and the dissolved hydrogen do not change by MG. On the other hand, when ground under the initial partial hydrogen pressure of 0.2 MPa, YNi2Hx is separated into two phases. The one is the α-phase, in which the solubility of a hydrogen is larger than that obtained by hydriding YNi2 without MG under the same condition, and the other is the α′-phase. The solubility of a hydrogen in α-phase gradually decreases with increasing the MG time, while the α′-phase is transformed into the amorphous phase upon further grinding. After grinding it for 1080 min, the α-phase is changed into YNi5. Excess Y left in the phase transformation will be dissolved into the amorphous phase and it will react with hydrogen to form YH2. These differences of the amorphization processes depending on the initial hydrogen pressures can be understood by considering the free energy variation in each phase by MG.

Original languageEnglish
Pages (from-to)1043-1050
Number of pages8
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Issue number11
Publication statusPublished - 1996


  • Amorphization
  • Free energy
  • Hydrogen
  • Hydrogenation
  • Laves phase
  • Mechanical grinding
  • Nonequilibrium crystalline phase
  • Phase separation
  • Yttrium-nickel


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