Synthesis of Nanocrystal-Embedded Bulk Metallic Glass Composites by a Combination of Mechanical Alloying and Vacuum Hot Pressing

Bulk metallic glasses (i.e., BMGs) have attracted a lot of research and development interest due to their unique properties. Embedding BMG composites with nanocrystals can further extend their applications. In this study, Ta-nanocrystal-embedded metallic glass powder was prepared via the mechanical alloying of (Cu60Zr30Ti10)91Ta9 composition for 5 h using starting elemental powders. The structural evolution during the mechanical alloying process was examined using X-ray diffraction, scanning electron microscopy, synchrotron extended X-ray absorption fine structure, transmission electron microscopy, and differential scanning calorimetry. The 5 h as-milled powder was then consolidated into a bulk sample using vacuum hot pressing with an applied pressure of 0.72, 0.96, and 1.20 GPa. The effects of the applied pressure during vacuum hot pressing on the structure of the obtained BMG were investigated. The experimental results show that Ta-nanocrystal-embedded metallic glass composite powder was prepared successfully after 5 h of mechanical alloying. The 5 h as-milled composite powder exhibited a large supercooled region of 43 K between the glass transition temperature of 743 K and the crystallization temperature of 786 K. Using vacuum hot pressing at 753 K for 30 mins with an applied pressure, dense nanocrystal-embedded BMG composites were synthesized. The relative density and the crystallization temperature of the BMG composites increased with increasing applied pressure. The nanocrystal-embedded BMG composites prepared at 753 K for 30 mins with an applied pressure of 1.20 GPa exhibited a relative density of 98.3% and a crystallization temperature of 786 K. These nanocrystals were Ta, Cu51Zr14, and other possible Cu-Zr-Ti alloys (e.g., Cu10Zr7) that were randomly dispersed within the glassy matrix.