Compositional Effect on the Two-Stage Enthalpy Relaxation of Metal-Metalloid Amorphous Alloys upon Annealing

The anneal-induced enthalpy relaxation behavior was examined calorimetrically for amorphous alloys of Fe-P, Fe-B, Ni-P, Ni-B. Fe-Ni-P, Fe-Ni-B and Fe-Ni-Co-P systems. When the alloys annealed at temperatures below T_g are heated, an excess endothermic reaction (enthalpy relaxation) occurs above the annealing temperature. T_a. The magnitudes of Δ_ and ΔH_ for the alloys of Fe-P. Fe-B, Ni-P and Ni-B containing only one metallic element first increase gradually with rising T_a and then rapidly at temperatures just below T_g, while their changes as a function of T_a for the alloys containing more than two metallic elements show a distinct two-stage splitting ; a low-temperature peak at about T_g-200 K and a high-temperature peak just below T_g, From the result that the addition of the second metallic element causes the two-stage splitting of the ΔC_ (T_a), it has been proposed that the low-temperature endothermic peak is attributed to short-range rearrangement of metal-metal atoms with weak bonding nature and the high-temperature peak to the long-range cooperative regrouping of metal-metalloid atoms which are composed of the skeleton structure in the metal-metalloid amorphous alloys. The mechanism for the appearance of the two-stage enthalpy relaxation has been investigated by the concept of two-stage distributions of relaxation times proposed previously by the present authors and the distinct two-stage splitting has been interpreted to be generated by the distinguishable difference in the ease of atomic rearrangement between metal-metal and metal-metalloid