Effects of cryogenic thermal cycling on a La-based metallic glass: Relaxation or rejuvenation?

Abstract

Despite tremendous efforts conducted to reveal the role of cryogenic thermal cycling (CTC) treatment played in the microstructural evolution of metallic glasses (MGs), the underlying mechanisms corresponding to rejuvenation (or relaxation) are still poorly understood. By altering the cycling number and temperature, in the present study, the effects of CTC on hardness and β relaxation behaviors of La60Ni15Al25 MG were evaluated. Intriguingly, the experimental results indicated the cycling number dependence on hardness and the activation energy of β relaxation Eβ following identical trends, and all samples exhibited rejuvenation first and then turned to relaxation after certain cycling numbers. Moreover, it is indicated that the MG with distinct microstructural states could exhibit identical hardness and Eβ, and this unique observation was proposed to be dominated by the mechanism correlated to the shear transformation zone (STZ) size and matrix-path between the percolated STZs.