Thermodynamics, surface properties and microscopic functions of liquid Al-Nb and Nb-Ti alloys

The energetics of mixing in Al-Nb and Nb-Ti liquid alloys have been analysed through the study of surface properties (surface tension and surface segregation), dynamic properties (chemical diffusion) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the frame of statistical mechanical theory in conjunction with quasi-lattice theory (QLT). The phase diagram of the Al-Nb system exhibits three intermetallic compounds in the solid state, while a relatively simple phase diagram of the Nb-Ti system indicates nearly ideal mixing behaviour in the liquid phase and two stable solid phases. Since the structure of a liquid alloy is in some respects similar to that of a crystal, the complex formation phenomenon in Al-Nb melts has been analysed by a quasi-lattice structural model for chemical complexes. The energetics and structural arrangement in Nb-Ti melts have been studied by the quasi-chemical approximation (QCA) for the regular solution model.