Influence of topologically close-packed clusters on the solidification pathway of metallic tantalum liquid under high pressure

Résumé fourni par la source

The main microstructures in metallic liquids (or supercooled liquids) play a decisive role in determining the final solidification pathway (crystallization or amorphization). However, what kind of microstructure plays a critical role is constantly explored and studied by scholars. Some of previous theoretical and experimental studies have suggested that icosahedron (ICO) clusters (or ICO short-range order) in metallic liquids possess lower energy than their corresponding crystals, and high abundance of ICO clusters can increase the nucleation barriers and promote amorphous transformation. Current research results indicate that the content of various clusters (especially ICO clusters) in many metallic liquids is relatively low. 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 are investigated by using molecular dynamic (MD) simulation, and the microstructure evolutions in different solidification processes are quantitatively analyzed through the average atomic energy, pair distribution function, and largest standard cluster analysis (LaSCA). The results show that, compared with the cluster with 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. At a pressure P∈[0, 8.75] GPa, the TCP clusters in Ta metallic liquid not only exhibit low energy and a highly stable state, but also are highly interconnected with each other and resist decomposition, thereby promoting the amorphous transformation of the Ta metallic liquid. At 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 in the liquid-solid transition process. In this stage, nucleation and growth of the body-centered cubic (BCC) embryo occur mainly in areas where TCP clusters are stacked sparsely, eventually Ta metallic liquid forms a perfect BCC crystal .

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