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

Abstract

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.