A simulation study of microstructure evolution during solidification process of liquid metal Ni

A molecular dynamics simulation study has been performed for themicrostructure evolution in a liquid metal Ni system duringcrystallization process at two cooling rates by adopting theembedded atom method (EAM) model potential. The bond-type indexmethod of Honeycutt--Andersen (HA) and a new cluster-type indexmethod (CTIM-2) have been used to detect and analyse themicrostructures in this system. It is demonstrated that the coolingrate plays a critical role in the microstructure evolution: below thecrystallization temperature $T_{rm c}$, the effects of cooling rateare very remarkable and can be fully displayed. At different coolingrates of $2.0times10^{13}$,K,$cdot$,s$^{-1}$ and$1.0times10^{12}$,K,$cdot$,s$^{-1}$, two different kinds ofcrystal structures are obtained in the system. The first one is thecoexistence of the hcp (expressed by (12 0 0 0 6 6) in CTIM-2) andthe fcc (12 0 0 0 12 0) basic clusters consisting of 1421 and 1422bond-types, and the hcp basic cluster becomes the dominant one withdecreasing temperature, the second one is mainly the fcc (12 0 0 0 120) basic clusters consisting of 1421 bond-type, and theircrystallization temperatures $T_{rm c}$ would be 1073 and 1173,K,respectively.