Relative stability of amorphous phase versus solid solution in the Ni–Ti system revealed bymolecular dynamics simulations

Abstract

We employ molecular dynamics simulations withn-body potentials to calculate the energies of solid solutions and metallic glasses in the Ni–Tisystem to reveal relative stability of two phases against the change of solute concentration. ForNi1−xTix alloys,the calculations show that the energies of the solid solutions are lower than the amorphous phases whenx≤0.24 and viceversa for x>0.24, in accord with thermodynamics analysis and experiments. To reveal the underlyingphysics responsible for this, the evolution of structures in the solid solutions and theamorphous phases are studied via the coordination number (CN) and common neighbouranalyses. The results show that, with an increase in Ti concentration, the total averagecoordination number is close to 12 for all solid solutions owing to the face-centred cubic(fcc) crystalline structure remaining, while it changes from less than 12 to greater than 12for the amorphous phases, suggesting that more bonds or more fractions of large CNs(>12) exist in the amorphous phases with a high Ti content. The relative stability of theamorphous phases versus the solid solutions revealed by the order of energy is thuscorrelated with the structural change of the amorphous phases.