Molecular Dynamics Simulation of Nucleation from Undercooled Melt of Nickel- Aluminum Alloy and Discussion on Polymorphism in Nucleation

S Orihara and Y Shibuta and T Mohri, MATERIALS TRANSACTIONS, 61, 750-757 (2020).

DOI: 10.2320/matertrans.MT-M2019353

Nucleation from undercooled melt of Ni-Al alloy is investigated by molecular dynamics (MD) simulation. Multiple nucleation of NiAl nuclei with B2 structure appears from undercooled melt of Ni-50 at%Al, which forms a fine microstructure of B2-NiAl. On the other hand, stepwise phase transition happens from undercooled melt of pure Ni, which is known as Ostwald's step rule. That is, body-centered-cubic (BCC) phase appears first from the undercooled melt and then face-centered-cubic (FCC) nucleation occurs from the inside of previously existing BCC nucleus. Origin of the polymorphism in stepwise nucleation of Ni and the preferential nucleation of B2-NiAl from melt of Ni-Al alloy is discussed on the basis of classical nucleation theory.

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