Fig. 1 TEM image of Cu45Zr45Ag10 metallic glass. a BF image shows homogenous contrast, and SAED pattern in the inset shows a halo ring typical of amorphous structure; b HREM image shows a maze-like pattern, indicating a fully amorphous structure

Fig. 2 a Preparation scheme of TEM sample cut by focused ion beam from the electrochemically polished sample, b the sample transferred onto the in situ heating chip by an ex situ nanomanipulator

Fig. 3 a, b HAADF images of Cu45Zr45Ag10 amorphous alloy acquired at 200 °C at a heating rate of 20 K/min and the EDX spectra in inset b, c HREM image of amorphous structure of both Ag-rich (circled dark area) and Cu-rich matrix, d SAED pattern showing a typical amorphous halo ring

Fig. 4 HAADF images showing the microstructure evolution of Cu45Zr45Ag10 amorphous alloy at 300 °C a, b and 380 °C c, d at a heating rate of 20 K/min. The growth and coalescence of Ag-rich nanospheres occur and a few Cu-rich nanocrystals precipitate at 300 °C (as indicated by bright arrow in b). Ag-rich nanospheres aggregate in a manner similar to grain boundary segregation in crystalline alloys (schemed by blue broken lines), followed by the rapid precipitation of Cu-rich nanocrystals in the remaining amorphous matrix at 380 °C c, d

Fig. 5 HAADF images showing the microstructure evolution of Cu45Zr45Ag10 amorphous alloy at 450 °C a, b, 500 °C c, d at a heating rate of 20 K/min. Ag-rich areas become crystallized and form a network-like structure at 450 °C, impeding further coarsening of Cu-rich nanocrystals at 500 °C

Fig. 6 Scheme of crystallization mechanism of Cu45Zr45Ag10 metallic glass. There are four typical steps: a phase separation into Ag-rich nanospheres (marked by blue dots) within 5 nm via nucleation and growth mode at 200 °C, b Ag-rich nanospheres aggregation in a manner similar to grain boundary segregation in crystalline alloys at 380 °C, c Cu-rich nanocrystals (marked by red rectangles) precipitated quickly from the remaining Cu-rich amorphous matrix at 380 °C, d crystallization and growth of Ag-rich nanospheres, forming a network-like structure, and thus retard the further coarsening of Cu-rich crystals