Melt fluidity and microstructure of bulk metallic glass under different cooling conditions

The bulk metallic glasses (BMGs) casting process should consider the glass transition and melt filling simultaneously, which is dependent on the melt fluidity and casting conditions. However, the impact of casting processes on the melt solidification and flow behavior of BMGs melt has not been thoroughly studied. Herein, the effect of cooling conditions on melt fluidity and microstructure of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 BMGs was systematically investigated by controlling the melt overheat and mold preheating temperature. The fluidity model for BMGs melt in a semicircular straight cavity was established, and the flow length of the melt under different cooling conditions was calculated based on the heat balance theory. The microstructure of the BMGs was characterized by using XRD, SEM, DSC and TEM. The results reveal that increasing melt overheat is more effective than raising mold preheating temperature in enhancing melt fluidity. Increasing them would lead to an increase of the order degree of the BMGs castings and crystallization, which is mainly related to the increase of critical cooling rate of BMGs. This work can provide a reference for the development of BMGs casting process.