Formation and evolution of topologically closepacked crystals during the rapid solidification of liquid metal tungsten

A series of molecular dynamics simulations were performed to investigate the phase transition during the rapid solidification of liquid metal tungsten (W). In particular, the formation and evolution of the topologically close-packed (TCP) crystals of beta-W have been thoroughly investigated in terms of the newly developed largest standard cluster analysis (LaSCA), tracing method, and 3D visual analysis. Results indicate that the system solidifies into the amorphous structure that coexists with TCP crystals rather than pure amorphous ones even at high cooling rates, and the content of the TCP crystals increases with decreasing cooling rate. The defects in the TCP crystal structure are the precursor of the perfect ones; at the beginning of crystallization, both the perfect TCP crystal structure and defect ones increase quickly with decreasing temperature, however, when the perfect TCP crystal structure become dominant in the system, the defective ones begin to gradually transform into perfect ones. Interestingly, the formation and evolution of the TCP crystals of beta-W experience three stages: the incubation of the crystal nuclei, formation and rapid growth of the critical nucleus, and slow growth and regulation of crystal nuclei. These findings shed new light on the understanding of the nucleation theory under rapid cooling of metal melts.