Zr-based bulk metallic glass composite with in situ precipitated nanocrystals

The authors report the formation of Zr₅₆Co₂₂Al ₁₆Ag₆ bulk metallic glass composites with in situ formed ultrafine nano precipitates, which are made by copper mold casting over a range of rod diameters from 2 to 20 mm. The precipitated phases were identified to be a mixture of ZrAl-type and AlZr₂-type phases with a grain size smaller than 5 nm. With increasing alloy rod diameter, the grain sizes of nanocrystals exhibit little change, while the volume fraction of nanocrystals increases. The large separation between the nucleation rate maximum and the growth rate maximum temperatures is proposed to mainly account for the ultrafine nanograin size and high nucleation rate, and the alloying effects of Ag are discussed for understanding the viscosity behavior changes of the Zr-Co-Al alloy melt. The present system is expected to be useful for studying the formation mechanism of bulk metallic glass nanocomposites in the liquid cooling process.