Modeling of the Sub-T_g Relaxation Spectrum of Pd_42.5Ni_7.5Cu₃₀P₂₀ Metallic Glass

We study the mechanical relaxation spectrum of Pd_42.5Ni_7.5Cu₃₀P₂₀ metallic glass. The effect of aging on the relaxation behavior is analyzed by measuring the internal friction during consecutive heating runs. The mechanical relaxation of the well-annealed glass state is modeled by fitting susceptibility functions to the primary and secondary relaxations of the system. The model is able to reproduce the mechanical relaxation spectrum below the glass transition temperature (sub-T_g region) in the frequency-temperature ranges relevant for the high temperature physical properties and forming ability of metallic glasses. The model reveals a relaxation spectrum composed by the overlapping of primary and secondary processes covering a wide domain of times but with a relatively narrow range of activation energies.