Metastable alloys synthesized by ion mixing in immiscible Ti-Nb and Ti-Ta systems

Room temperature 200 keV xenon-ion irradiation of multilayers, designed to include sufficient fraction of interfacial atoms, resulted in the formation of amorphous alloys in the immiscible Ti-Nb aid Ti-Ta systems, which have previously been recognized as non-glass forming ones because of their positive heats of formation and some other factors. In addition, some metastable crystalline f.c.c. phases were also obtained. To explain the unusual alloying behaviors, Gibbs-free-energy diagrams of the systems were constructed based on Miedema's model and showed that the interfacial free energy originating from chemical and elastic contributions elevated the multilayered films to an energy level higher than those of the observed amorphous and metastable crystalline phases, thus generating a driving force for alloying in these immiscible systems. Meanwhile, the possible growth kinetics of the metastable crystalline phases are also discussed. (C) 1998 Elsevier Science S.A. All rights reserved.