Study of metastable alloy formation by thermodynamic calculation and ion beam manipulation in an equilibrium immiscible Au-W system

Based on thermodynamic calculations, a Gibbs free energy diagram was constructed to predict the possibility of metastable alloy formation in the equilibrium immiscible Au-W system characterized by a large positive heat of formation of +17kJ/mol. Accordingly, in the properly designed Au-W multilayered films, a unique super-saturated fcc solid solution was obtained by ion beam irradiation on the Au-rich side. More interestingly, on the W-rich side, an amorphous alloy was formed through a two-step structural transition. First, a low dose (2×10¹⁵ Xe⁺/cm²) irradiation resulted in the formation of a super-saturated bcc solid solution. Second, the bcc solid solution transformed into an amorphous state upon further irradiation up to a dose of 8×10¹⁵ Xe⁺/cm². We report, in this paper, results of thermodynamic calculations and the experimental observations concerning the metastable alloy formation in the Au-W system together with a brief discussion of the structural transition mechanism.