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Bulk metallic glasses (BMGs) bear versatile advantages compared to traditional crystalline metallic materials. However, preparation of large size BMG components remains a great challenge due to the lack of understanding the casting dynamics of BMGs. The present work investigates the dynamics of the solidification process during casting of a Zr41.2Ti13.8Cu12.5Ni10Be22.5BMG by measuring the time-dependent temperature evolution and constructing distance-time curves showing the progress of solidification. The experimentally probed temperature evolution proves that a higher casting temperature causes a lower cooling rate and induces more pronounced nanocrystal phase formation in the final BMG casting. Thus, optimization of the casting temperature is crucial for casting BMG components. The solidification coefficient Kof the studied Zr-based BMG in copper mold was determined. The solidification time can be calculated with model: τ=M2K2. The solidification of the Zr-based BMG occurs in a narrow transition layer region following a “layer-by-layer” solidification mode. This feature is vital for designing the casting process appropriately to avoid the formation of casting defects in BMG components. The present work sheds new light on the solidification mechanism of bulk glass-forming liquids and underlines the importance of optimizing the technology and processing conditions for fabrication of BMG components with practical applications.

Most of the metallurgical defects in castings can be initiated by oxide bifilms reported in various alloys. However, investigations of bifilm defects in nickel-aluminium bronze castings and their fracture behaviors were absent to date, which was explored in the present work. The results showed that there are two types of defects, i.e. smooth oxide film separating from the alloy matrix (old bifilm) and crinkled oxide film tightly adhering to the matrix (young bifilm). Thermodynamics and energy spectrum analysis proved that the bifilm was Al2O3. The inferred bifilm thickening speed curve also suggests that they come from different stages of the casting process. A fracture model was proposed to understand the fracture behaviors associated with the Young's modulus of the two types of bifilm defects. These results will shed new light on the understanding of bifilm defects failure and improve the defect control of castings.