Theoretical Model Of Formation Enthalpy For Ternary Alloy And Its Application In Prediction Of Phase Transformation Of Aluminum Alloy

The formation enthalpy is the most important thermodynamic parameters of alloy. The formation enthalpy of multi-alloy plays an important role in metallurgy, materials processing as well as the multiscal simulation of microstructural evolution and properties of alloys in the forming process. It is hard to experimentally measure all of the thermodynamic parameters for all alloys because of the tremendous amount of data as well as the limited experimental conditions. Therefore, it is necessary to theoretically predict thermodynamic properties of alloys. This paper studied the main factors influencing the formation enthalpy of ternary alloy and has established a theoretical model of formation enthalpy for ternary alloy. It is of great significance for the further study of the formation enthalpy for commercial alloy and practical applications.Theoretical analysis shows that the change of the electron density, the electronegativity and the atomic contact surface area has a large influence on the formation enthalpy. It is found that when adding to the binary system a third alloying element, the change of the electron density and electronegativity of the original component is proportional to the average value of electronegativity of said component and the third one. Thus we obtain the contribution of corresponding binary sub-system of the investigated system. Finally the model of formation enthalpy for ternary alloys is established. By using the proposed model, the formation enthalpy of such alloys as Ni64Zr36Cu, Ni36Zr64Cu, Ni36Zr64Al, Al27Ni73Cu, Ni4Cu6Al, Cu49Al51Ni, Al62Zr38Cu, Zr2Cu8Al, etc., is predicted. The calculated results are superior to that of Zhou model and Toop model, and well consistent with the experimental results. The application of the present model to the estimation of the excess Gibbs free energy of alloys is simple and effective. The calculated result for Sb-Bi-Ga alloy is in good agreement with the experimental data. In this paper, a preliminary study was made to calculate the phase-transformation of alloys. The calculated result for Al-Si alloys in Al-rich zone is in agreement with the phase diagram data.The influence of the change of the electron density, electronegativity, atomic surface area of contact affect on the formation enthalpy of alloy is obtained in this dissertation. The established model for tenary alloys can be used for the multiscale simulation of the materials forming process as well as the optimization of the processing parameters.