A statistical-thermodynamic modeling of behavior and properties in thin-film intermetallics with D019-structure

Abstract

Abstract A statistical-thermodynamic modeling based on Ising approach and Bethe–Bragg–Williams approximations is proposed for description of ordering phenomena and thermodynamic behavior in nano-crystalline thin-film materials with D0 19 -structure. New modeling approach takes into account presence of all possible defects in the structure, both vacancies and anti-structure atoms and includes a description of long-range and short-range ordering in the crystal lattice. The derived equations define the fluctuations of internal variables, such as pair interaction energies between atoms and defects and their contributions to macroscopic properties. The variation of defect concentrations, ordering tendency, and thermodynamic activities as a function of number of monoatomic layers, temperature and composition are derived. The obtained theoretical results are tested using experimental data on thermodynamic activity for bulk intermetallic phase such a Ti 3 Al. It was shown that the bulk behavior in nano-Ti 3 Al is approached with a thickness of about 100 layers.