Freezing of Ni−Al Bimetallic Nanoclusters in Computer Simulations

Bimetallic particles have two features not observed in one-component systems: surface segregation and compositional ordering. Molecular dynamics simulations have been performed to study the freezing of Ni−Al nanoclusters at different compositions. It was found that for Al-rich and equiatomic compositions the surface segregation of Al atoms inhibits nucleation, causing supercooled clusters to solidify to an amorphous aggregate. In the case of Ni 3 Al particles, where there are not enough Al atoms to complete the surface layer, clusters froze to multiply twinned structures with well-defined local translational order but, owing to the fast kinetics of solidification, with compositional disorder.