Thermodynamic modeling of Al–Si nanoalloy phase diagram

Due to large surface to volume ratio, phase transformation of materials at nanoscale occurs at lower temperatures compared to bulk materials. The changes in the equilibrium phase diagram with the change in particle size of the constituents of Al–Si system has been calculated with the help of classical theory employing CALPHAD method for calculations having size less than 10 nm. In the calculation of size-based phase diagram of Al–Si, surface energy term has been added to Gibbs energy values available in the Al–Si thermodynamic database to accommodate the change in the particle size. Surface tension of Al–Si alloys is formulated using Butler equation and with the help of Redlich–Kister polynomials, excess Gibbs-free energy of nanoparticles in Al–Si system has been calculated considering particle size as 2 and 10 nm. Calculated results extend the thermodynamic information about the Al–Si system from bulk to nanomaterials. With the decrease of particle diameter, change in thermodynamic properties of the Al–Si system has been observed. Also, reduction in eutectic temperature, eutectic composition, and melting temperature of the constituents were observed. Liquidus and solidus boundaries of Al–Si phase diagram are also shift towards the lower temperature.