Irradiation-induced alloying in an immiscible TaTi system

Abstract

In the properly designed multilayered films according to an interfacial free energy estimation, amorphous alloys were formed upon room temperature 200 keV xenon-ion irradiation in the TaTi system, although it was previously considered as a non-glass forming one because of its positive heat of formation as well as the unfavored atomic size and electronegativity. In addition, two metastable Ta-rich and Ti-rich fcc phases of different lattice constants were also obtained. To explain the unusual alloying behaviors, a Gibbs-free-energy diagram of the system was constructed based on Miedema's model. The calculated diagram showed that the interfacial free energy resulting from chemical and elastic contributions in the films could raise the initial energetic state of the multilayered films to a state higher than those of the observed amorphous and metastable crystalline phases, thus generating a driving force for alloying in this immiscible TaTi system. The possible growth kinetics of the metastable crystalline phases is also discussed.