Intrinsic brittleness origination of micro-scale phase-separating metallic glasses: Based on mechanical relaxations and theoretical analysis

Abstract

Pronounced slow β-relaxation in metallic glasses (MGs) has been proven to be closely related to macroscopic plasticity especially around 0.6–0.8Tg. However, the micro-scale phase-separating (ZrxLa1-x)57Co27Al16 (x = 0.2, 0.3, and 0.4) MGs obviously display brittleness around 0.7Tg even though an obvious slow β-relaxation peak is observed based on the dynamic mechanical analysis (DMA). In order to probe their intrinsic brittleness, the slow β-relaxation processes of the (ZrxLa1-x)57Co27Al16 (x = 0, 0.2, 0.3, 0.4, and 1) MGs were observed together with their mechanical performances. The results demonstrated that the La57Co27Al16 and Zr57Co27Al16 MGs show obvious ductility around 0.7Tg. Based on DMA results, the La57Co27Al16 MG displays an evident slow β-relaxation peak while the Zr57Co27Al16 MG presents an excess wing. When the phase-separating Zr–La–Co–Al MGs consisting of La-rich and Zr-rich components were heated up to 0.7Tg, only the β-relaxation behavior originating from La-rich components rather than from Zr-rich components is preferentially thermal-activated. In addition, the slow β-relaxation is well described by the Cole-Cole (CC) model, which becomes more obvious with increasing phase-separating degree. Then only partial but not all of potential structural units in whole samples can be activated, leading to the whole intrinsic brittleness of the micro-scale phase-separating MGs. These findings suggests that the large compositional difference between components is harmful to design ductile phase-separating MGs.