The effect of HCP on the formation of twin boundaries and dislocations in Ni–Co alloys

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In this study, molecular dynamics (MD) was used to simulate the rapid solidification process of Ni 47 Co 53 and Ni 48 Co 52 alloys at a cooling rate of 10 12 K/s. The effects of HCP on the formation of twin boundaries and dislocations in two Ni–Co alloys are studied. It is found that the difference of HCP clusters is the main effect that producing discrepancies on microstructure of two alloys. The number of HCP clusters accounted for 9.23% in Ni 47 Co 53 alloy. They are regularly arranged to form the number of single-layer twin boundaries, and each twin boundary ends in a dislocation. The FCC and HCP structures coexist in the same atomic layers, which is easy to create dislocations. The relatively standard FCC crystal and only 0.32% HCP clusters are formed in Ni 48 Co 52 alloy at 300 K. That small amount of HCP clusters are dispersed on the surface, and cause the formation of dislocation in the border with FCC clusters. • Ni 47 Co 53 undergoes only one phase transition, while Ni 48 Co 52 undergoes two phase transitions. • HCP with a proportion of 9.23% are formed in Ni 47 Co 53 , but only 0.32% HCP are formed in Ni 48 Co 52 . • The connection modes are mostly FCC-FCC and FCC-HCP in Ni 47 Co 53 , while almost only FCC-FCC are formed in Ni 48 Co 52 . • HCP is arranged in a single layer to form twin boundaries in Ni 47 Co 53 , but HCP is dispersed on the surface in Ni 48 Co 52 .