Pressure Dependence of Hydrogen-Induced Amorphization in C15 Laves Phase TbFe₂

Abstract

The pressure dependence of structural changes of C15 Laves phase TbFe₂ heated in a hydrogen atmosphere was investigated using a pressure differential scanning calorimeter (PDSC), a powder X-ray diffractometer (XRD), a differential scanning calorimeter (DSC) and a hydrogen analyzer. Hydrogen absorption in the crystalline state, hydrogen-induced amorphization (HIA), precipitation of TbH₂ and decomposition of the remaining amorphous alloy into α-Fe and TbH₂ occurred exothermally with increasing temperature above 0.5 MPa H₂, independent of the heating rate. HIA and precipitation of TbH₂ occurred simultaneously in 0.2 MPa H₂ (0.33 K/s) and in 0.1 MPa H₂ (0.17 K/s). On the contrary, hydrogen absorbed crystalline c-TbFe₂H_3.5 decomposed directly into α-Fe and TbH₂ in 0.1 MPa H₂ (0.33 K/s). That is, no amorphous phase was formed at the lower hydrogen pressure and at a high heating rate. The reason why HIA occurs above the critical hydrogen pressure and below the critical heating rate was discussed on the basis of the hydrogen content absorbed in the crystalline state of TbFe₂.