Isothermal nanocrystallization behavior of bulk metallic glass composites in supercooled liquid region

Bulk metallic glass composites (BMGCs) reinforced by micro- (spherical size of about 10 μm) and nano-sized (20–50 nm) Al₃Zr crystals were synthesized by copper mold suction casting method. The isothermal crystallization of Cu₄₀Zr₄₄Ag₈Al₈ BMGCs in the supercooled liquid region was studied by differential scanning calorimeter (DSC), X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanisms for nucleation and growth of the crystalline phases precipitated in two-stage crystallization process and the effect of the isothermal treatment on the in situ crystalline phases were discussed. Results show that the BMGCs experience a primary crystallization process. Nano-sized Al₃Zr and Cu₁₀Zr₇ phases precipitate from the amorphous matrix successively. Furthermore, isothermal annealing has no effect on the pre-existing particles in the as-cast sample, which creates a new method to synthesize BMGCs strengthened by duplex crystalline phases with a large size difference. And the reinforced phase could also be dominated with intention if the as-cast BMGCs preparation and isothermal treatment process can be controlled more accurately.