Main and secondary relaxations in an Au-based bulk metallic glass investigated by mechanical spectroscopy

The dynamic mechanical relaxation behavior of an Au₄₉Cu_26.9Si_16.3Ag_5.5Pd_2.3 (at.%) bulk metallic glass was investigated by mechanical spectroscopy as a function of temperature or driving frequency. The mechanical spectra show the evidence of a secondary relaxation (or β) process at low temperature or high driving frequency. The main relaxation (α) is clearly evident at higher temperature or lower frequency. Crystallization induces an increase in elastic modulus, in two steps, which correspond to the formation of two different crystalline phases, as determined by in-situ X-ray diffraction experiments. Master curves could be obtained based on the time-temperature superposition principle. From these curves the apparent activation energies for the two relaxation phenomena were determined: E_β = 1.10 eV and E_α = 3.65 eV, respectively. These values indicate that the secondary relaxation may be attributed to local atomic movements, while the α relaxation corresponds to correlated movements.