Nucleation mechanisms involving in rapid solidification of undercooled Ni_80.3B_19.7 melts

Ni_80.3B_19.7 alloy was undercooled using glass-fluxing and cyclic superheating method. The solidification process was observed by a high-speed video system. On this basis, the nucleation mechanisms involving in rapid solidification of undercooled Ni_80.3B_19.7 melts were investigated. The calculation based on the classical nucleation theory demonstrated that in the achieved range of undercooling (ΔT) due to Ni₃B phase possesses a higher nucleation rate than that of α-Ni phase, Ni₃B phase can always solidify as the primary phase, which is in accordance with the experimental observations. Further, the analyses of experimental results and the calculation in terms of the transient nucleation theory indicated that the time required to form the critical nucleus is much shorter than the time required for solid/liquid (S/L) interface to touch the nucleus, and this will lead to the occurrence of the copious nucleation in the undercooled Ni_80.3B_19.7 melt.