On the Phase Formation During Ion-Beam Mixing

ABSTRACTThe phase formation during ion-beam mixing of binary transition-metal alloys has been studied by use of Xe* , Ar* , and Ne* as a function of temperature and composition. Especially the composition ranges, where only amorphous phases occur, i.e., the glass-forming ranges, have been investigated. Based on semiempi-rical data on free energies, metastable phase diagrams have been constructed and glass-forming ranges estimated for the case of negative heat of mixing. Taking into account the quite large uncertainties of the applied thermodynamic data, reasonable agreement is observed between estimated and experimental glass-forming ranges. In the case of positive heat of mixing, the initial thin-film structure is near thermodynamic equilibrium. However, for small values of the heat of mixing, it is still possible to form amorphous structures. In the absence of chemical driving forces, this formation cannot be explained in a similar way as in the case of negative heat of mixing. As the nucleation of crystalline phases may differ with and without irradiation, irradiation of amorphous structures at elevated temperatures may create new metastable phases. Preliminary measurement of crystallization of metallic-glass films during irradiation are reported.