Discussion on nucleation mechanism of undercooled Ni80.3B19.7 melts

Ni80.3B19.7 alloy was undercooled using the glass-fluxing method. Applying high speed video (HSV) and metallographic methods, the recalescence behavior and as-solidified microstructure were observed. In combination with the analysis of the experimental results and the calculation on the basis of time dependent nucleation theory, the nucleation mechanism in undercooled Ni80.3B19.7 melt was investigated. Owing to the time required to form the critical nucleus is much smaller than the time required for solid/liquid (S/L) interface to touch the nucleus, the critical nucleuses ahead the S/L interface can form and develop into the nucleation events, which make the copious nucleation ahead the S/L interface be operative. The calculation is in quantitative agreement with the experimental results.