METASTABLE PHASES FORMED BY ION MIXING IN THE HF-NB SYSTEM WITH A POSITIVE HEAT OF FORMATION

Amorphization was achieved in the Hf-Nb system with a positive heat of formation (+6 kJ mol(-1)) by room-temperature 200 keV xenon ion mixin g of multilayered films. On the basis of thermodynamic calculation, in which the interfacial free energy of multilayered films was specially taken into account, a Gibbs free-energy diagram was constructed and a relevant interpretation to the observed amorphization behaviour was p roposed together with the kinetic considerations for the ion irradiati on process. Also, two metastable FCC phases of Nb-rich and Hf-rich con centrations with different sizes were obtained by ion mixing.