Critical Solid Solubility of the Ni-Ti System Determined by Molecular Dynamics Simulation and Ion Mixing

Abstract

From a realistic n-body potential of the Ni–Ti system, the critical concentrations of the Ni- and Ti-rich solid solutions were determined by molecular dynamics (MD) simulation to be 38 at% Ti and 15 at% Ni, respectively, beyond which a disordered atomic configuration was more stable than the respective crystalline solid solutions. It follows that the central composition range bounded by the critical solubilities, i.e. within 38–85 at% of Ti, can be considered as the glass-forming range of the system, which was confirmed by room temperature 200 keV xenon ion mixing of alternately deposited Ni–Ti multilayered films. Moreover, MD simulation of a Ni–Ti bilayer revealed that during the solid-state amorphization reaction, the growth of the amorphous interlayer followed exactly a t1/2 law and grew faster towards the Ti lattice than to the Ni side. The physical origin of such an asymmetric behaviour was found to be due to a difference in critical solid solubilty of the constituent metals.