Three mechanical relaxation modes associated with nanoscale structural heterogeneity in Pd42.5Ni7.5Cu30P20 fragile glass

Abstract

The dynamic relaxation behavior of Pd42.5Ni7.5Cu30P20 metallic glass was studied at 173–563 K (∼0.98Tg) and at angular frequency 10−2 to 102 rad s−1. Master curves of 16-digit dynamic moduli at angular frequency 10−4 – 1012 rad s−1 were constructed and characterized by the stretched exponent relaxation function, which exhibits three discrete relaxation modes with different activation energies, i.e., α-relaxation (7.98 eV) associated with the cooperative motion of ∼5 atoms, slow β-relaxation (1.39 eV) associated with single atomic diffusion, and fast β-relaxation (0.25 eV) associated with rattling motion. These three modes were also detected as slope changes on the quasi-static creep compliance under an isochronal heating process, which was successfully reproduced by dynamic complex compliance using the dynamic moduli with fitting parameters related to the considerable inhomogeneous structural characteristics, elastic modulus and volume fraction, generated in the glass.