Visco-elasticity and mechanical relaxation behavior in La-based metallic glasses

Abstract

Dynamic mechanical relaxation process is one of the important issues to understand mechanical/physical properties of metallic glasses. In the current research, dynamic mechanical relaxation behavior of La62Al14(Cu5/6Ag1/6)20(Ni1/2Co1/2)4 and (La0.7Ce0.3)65Al10Co25 bulk metallic glasses were investigated by mechanical spectroscopy. Unlike the typical Zr- or Cu-based metallic glasses, (La0.7Ce0.3)65Al10Co25 metallic glass shows an evident β relaxation process. On the other hand, La62Al14(Cu5/6Ag1/6)20(Ni1/2Co1/2)4 metallic glass presents a “shoulder” relaxation process. Physical aging below the glass transition temperature Tg induces a decrease of the concentration of “defects”, which corresponds to a reduction of the intensity of the β relaxation. During aging process, the amplitude of β relaxation (△E") decreases, while the relaxation time (τβ) increases. In organic glasses, it was reported that the changes of In(τβ) and In(△Emax) are linearly correlated with In(τβ)=b-a In(△E"max), this correlation has also been found in metallic glass. This behavior is discussed in the framework of the asymmetric double well potential (ADWP) model, and U and △ are used to characterize ADWP. It is suggested that during the aging process, the U/△ ratio remains basically unchanged, which is close to the coefficient describing the linear correlation between In(τβ) and In(△Emax) (U/△~a).