A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu70Ni30 adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2 × 1012 K/s, the Cu70Ni30 formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be further understood.
ZHENG Caixing LIU Rangsu ZHOU Qunyi TIAN Ze'an WANG Xin LI Qiang
A molecular dynamics (MD) simulation study has been performed for the solidification processes of two binary liquid alloys Ag6Cu4 and CuNi by adopting the quantum Sutton-Chen many-body potentials. By analyzing bond-types, it is demonstrated that at the cooling rate of 21012K/s, the CuNi forms fcc crystal structures, while the Ag6Cu4 forms amorphous structures. The original reason is that the atomic radius ratio (1.13) of the CuAg is bigger than that (1.025) of the CuNi. This shows that the atomic size difference is indeed the main factor for forming amorphous alloys. Moreover, for Ag60Cu40, corresponding to the deep eutectic point in the phase diagram, it forms amorphous structure easily. This confirms that as to the forming tendency and stability of amorphous alloys, the alloying effect plays a key role. In addition, having analyzed the transformation of microstructures by using the bond-type index and cluster-type index methods, not only the key role of the icosahedral configuration to the formation and stability of amorphous alloys can be explained, but also the solidification processes of liquid metals and the characteristics of amorphous structures can be further understood.
A molecular dynamics simulation study has been performed for a large sys- tem consisting of 100000 liquid metal Al atoms to investigate the formation and magic number characteristics of the cluster configurations formed during the rapid solidification processes. The cluster-type index method (CTIM) has been adopted to describe various types of cluster configurations. The results indicate that the icosahedral clusters (12 0 12 0) and their combinations play the most important role in the microstructure transitions during solidification processes; for the cluster configurations of different levels formed by various combinations with differing numbers of basic clusters, their size distributions possess ob- vious magic number sequence which is in turn as 13(13), 19(21), 26-28(27), 32-33(32), 39-40, 43-44, 48…, (those in bracket are the corresponding value in liquid state); the magic numbers correspond to the peak value positions of the cluster numbers for corre- sponding level formed with various combinations by 1, 2, 3, 4, 5, 6, 7, …basic clusters, respectively. This magic number sequence is in good agreement with the experimental results obtained by Harris et al. At the same time, this simulation study also gives a scien- tific and reasonable explanation to these experimental results.
LIU Rangsu1, LIU Fengxiang1, DONG Kejun1, ZHENG Caixing1, LIU Hairong2, PENG Ping2 & LI Jiyong3 1. Department of Physics, Hunan University, Changsha 410082, China
