Metastable alloys synthesised by ion mixing and thermodynamic and kinetic modelling

This paper presents some new results obtained by the authors in some 15 binary metal systems and a brief summary concerning ion mixing (IM) synthesis of metastable alloys. (1) The metastable crystalline (MX) phases so far obtained can be classified into five types, i.e. the super-saturated solid solutions and the enlarged hcp-I phases in hcp- or fee-based alloys reported earlier, and the newly formed fcc-I phases in hcp-based alloys, the fee-II and hcp-II phases in bcc-based alloys. The growth kinetics of the MX phases is also discussed. (2) The interfacial free energy in the multilayered films was found to play an important role in IM induced amorphization. By adding sufficient interface, amorphous alloys can be formed by IM in a broad composition range even in a system with rather positive heat of formation (Delta H-f), which has been predicted to hinder amorphization, (3) Gibbs free energy diagrams of some systems were constructed based on Miedema's theory. The calculation included the free energy curves of all the competing phases, especially those of the new MX phases. To check the relevance of the calculation, steady-state thermal annealing of the multilayered films was conducted and the results confirmed the calculated energetic sequence of the competing phases. The constructed diagrams can interpret the formation and evolution of the metastable phases synthesised by IM.