Study on the dislocation mechanism of Ni47Co53 alloy during rapid solidification

Abstract

Abstract Dislocations and other atomic-level defects play a crucial role in the macroscopic properties of crystalline materials, but it is extremely difficult to observe the evolution of dislocations, due to the limitations of the most advanced experimental techniques. Therefore, in this paper, the rapid solidification process of Ni47Co53 alloy at five cooling rates is studied by molecular dynamics simulation, and the evolutions of microstructure and dislocations are investigated. The results show that FCC are formed at the low cooling rate, and the crystalline and amorphous mixture appear at the critical cooling rate, and the amorphous are generated at the high cooling rate. The crystallization temperature and crystallinity decrease with the increasing of cooling rate. Dislocations are few at the cooling rates of 1*1011, 5*1012 and 1*1013 K/s, and they are most abundant at the cooling rates of 5*1011 and 1*1012 K/s, which both of their lengths are almost identical. A large number of dislocation reactions exist in both cooling rates, in which the interconversion of perfect and partial dislocations is primary. The dislocation reactions are more intense at the cooling rate of 5*1011 K/s, and the slip of some dislocations leads to the interconversion between FCC and HCP, which causes the disappearance of TBs. FCC and HCP are in the same atomic layer and dislocations are formed at the junction due to the existence of TBs at the cooling rate of 1*1012 K/s. The investigation is important for understanding the dislocation mechanism and its influence on crystal structure at atomic scales.