The primary microstructures in metallic liquids (or supercooled liquids) play a decisive role in determining the final solidification pathway (crystallization or amorphization). However, the question of which specific microstructures play a critical role has attracted widespread attention from scholars. Some previous theoretical and experimental studies have suggested that icosahedron (ICO) clusters (or ICO short-range order) in metallic liquids possess lower energy than crystals, and a high abundance of ICO clusters can increase the nucleation barrier, promoting amorphous transformation. Current research results indicate that the content of various clusters (especially ICO clusters) is low in many metallic liquids. Therefore, it is significant to identify which microstructure plays a critical role in metallic liquids.
In this work, the rapid solidification processes of tantalum (Ta) metallic liquid under various pressure conditions were investigated using molecular dynamic (MD) simulation, the microstructure evolution during different solidification processes is quantitatively analyzed through the average atomic energy, pair distribution function, and largest standard cluster analysis (LaSCA). The results show that, compared to the low content of ICO, topologically close-packed (TCP) clusters are not only more abundant but also play a more decisive role in determining the solidification path of Ta metallic liquids. Under pressure P∈[0, 8.75] GPa, the TCP clusters in Ta metallic liquid exhibit low energy, and a highly stable state as well as highly interconnected and resistant to decomposition, thereby promoting the amorphous transformation of the Ta metallic liquid. Under pressure P∈[9.375, 50] GPa, the TCP clusters in Ta metallic liquid are in a metastable state, many TCP clusters with high energy state can easily transform into other clusters during the liquid-solid transition process. At this stage, nucleation and growth of the body-centered cubic (BCC) embryo primarily occur in areas where TCP clusters are stacked sparsely, eventually forming a perfect BCC crystal from Ta metallic liquid.