Comparing Thermodynamic and Surface Energy models to evaluate and reassess Copper-Nickel bulk and Nano Phase Diagrams

In the present work, Cu-Ni phase diagram is evaluated and assessed using the CALPHAD method for the accurate prediction of liquidus and solidus curves. Phase diagrams were plotted for both bulk and nanoalloys. Phase diagrams for nanoparticles are significantly different from that of the bulk because the melting point of the nanoparticle is a function of particle size. The melting point of the nanoparticle is determined using two different models, Surface Energy model and Enthalpy and Entropy model. Phase diagrams were plotted using both models for Copper-Nickel binary isomorphous system and were compared with the experimental data. It was found that the Enthalpy and Entropy model is in good agreement with the experimental data compared to the Surface Energy model. This is because the Enthalpy and Entropy model considers the thermal interactions at various temperatures whereas the surface energy model only considers the surface free energy of the particle. Also, Enthalpy and Entropy model is a dynamic model because it can predict the melting enthalpy and entropy of the nanoparticles for various particle sizes which result in accurate free energies predictions. Hence, phase diagrams that are predicted using Enthalpy and Entropy model tend to be more accurate than that of the surface energy model.