2020 Volume 61 Issue 4 Pages 750-757
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.