Unusual alloying behavior observed in the immiscible Ag-Mo and Ag-Nb systems under ion irradiation

Free energy diagrams for the Ag-Mo and Ag-Nb systems which have very large positive heats of formation at equi-atomic stoichiometry, +56 and +25 kJ/mol, respectively, were constructed which included consideration of the interfacial free energy present in multilayered films. The calculated diagrams suggested that amorphization was thermodynamically achievable in both systems despite their large positive heats of formation. In the case of Ag-Mo multilayers containing 12 layers, the calculated predictions of amorphization favored Ag-and Mo-rich alloys, in agreement with experimental results of ion mixing conducted at liquid nitrogen temperature. Additionally, new metastable FCC Mo-and Nb-enriched phases were obtained at different irradiation doses. More interestingly, these FCC phases transformed into amorphous states after room temperature aging. This FCC to amorphous transition was also discussed by comparing the free energy of these states. (orig.)