FORMATION CONDITIONS AND CRYSTALLIZATION OF HYDROGEN-INDUCED AMORPHOUS SMNI2HX, GDNI2HX, DYNI2HX, HONI2HX, ERNI2HX ALLOYS

Amorphous single phase were isothermally formed by hydrogenation of the C15 Laves compounds RNi2 (R = Sm, Gd, Dy, Ho, Er) at 400 K and 5.0 MPa, H2 for 86.4 ks. The formation range of each phase was examined as a function of the hydrogenation temperature and the hydrogen pressure in the RNi2 (R=Sm, Ho, Er) compounds. The amorphous single phase was formed below about 500 K independent of the hydrogen pressure in SmNi2. On the other hand, it was formed in the ange of 300-523 K and 2.0-5.0 MPa H2 in HoNi2, and in the range of 400-500 K and 4.0-5.0 MPa H2 in ErNi2. The crystallization behavior of the amorphous a-RNi2Hx alloys prepared by hydrogenation was investigated by differential scanning calorimetry (DSC). The amorphous alloys decomposed into c-RNi5+c-RH2 in the case of R=Sm and Gd, while they decomposed into c-RNi3+c-RH2 in the case of R=Dy, Ho and Er. Apparent activation energies for crystallization in these amorphous alloys were almost constant as about 150 kJ/mol in spite of the different crystallization behavior. Enthalpy changes in crystallization were about 3.7 kJ/mol except for ErNi2Hx. The crystallization temperatures of these amorphous alloys ranged from 628 to 672 K.