Dynamic mechanical analysis in La-based bulk metallic glasses: Secondary (β) and main (α) relaxations

Relaxation behavior was investigated in typical La-based bulk metallic glasses by dynamic mechanical analysis, both in the isochronal and in the isothermal routes. Two relaxations were observed: the main relaxation (α), associated with the glass transition, and a secondary relaxation, at lower temperature or higher frequency. This secondary relaxation corresponds to the well known Johari-Goldstein (JG) β relaxation. Master curves can be obtained. The activation energy Eβ of β relaxation (about 1 eV) is in agreement with the empirical relation Eβ ≈ 26(±2) RTg. The high value of the activation energy Eα of the α relaxation (about 5 eV) indicates that this relaxation corresponds to correlated movements. The mechanism of JG β relaxation in metallic glasses is discussed.