Thermodynamic Analysis of Solid Solution Formation in the Nanocrystalline W-Co-Si Ternary System by Mechanical Alloying

Co3W2Si intermetallic compound was synthesized by mechanical alloying (MA) of W, Co and Si elemental powder mixtures. The phase composition of the milled products was evaluated by X-ray diffraction (XRD) analysis. Morphological evolutions were characterized by transmission electron microscopy (TEM). The results showed that high energy ball milling performed in the present work led to the formation of Co3W2Si intermetallic phase after 50h MA. A thermodynamic analysis of the process was then carried out using Miedema model. The thermodynamic results showed that there exists a positive thermodynamic driving force in W–Si and Co-Si binary systems and W-Co-Si ternary system to form a solid solution at all compositions but Gibbs free energy change in Co-W binary system is positive for solid solution formation. So that there is no thermodynamic force to form a solid solution in Co-W system. In Co-W-Si ternary system, the addition of elemental W to Co3Si compound decreases Gibbs free energy change and a more stable structure is formed.