Multi-Phase Field Numerical Simulation Of Lamellar Growth Morphology Stability In Pb-Sn Eutectic Alloys

Due to the microstructure in the formation of the casting playing a decisive role in the mechanical properties and the serving life, the effective controlling the formation of microstructure of castings in the forming process have extraordinary scientific and engineering significance in the process of solidification. Eutectic lamellar microstructure, as a kind of common microstructure, exists widely in phase transformation of many important structural materials and functional materials. As for scientific research workers, one of the main problems of eutectic fields is how to accurately obtain the information of the eutectic organization evolution and transformation during the process of eutectic solidification. It is difficult to achieve the parameters that the controlling the forming process needs with whole the experimental methods, while the numerical simulation methods can overcome these difficulties, therefore, the numerical simulation of microstructure method has been gained attention.The phase field method, as a kind of effective microstructure simulation method, has been highlighted in the study of microstructure evolution and can simulate effectively the solidification process of castings by coupling the other external fields.Based on the KKSM multi-phase field model, the steady state solidification process of Pb-Sn eutectic alloy was simulated, and based on the Pb-Sn eutectic alloy the influencing factors of the stability of eutectic layer were researched in this paper. Research results show that:(1)The growth process of the directional solidification of Pb-Sn eutectic alloy was simulated by coupling KKSM multi-phase field model and CALPHAD. The simulation results had a good fit with the fundamentals.(2)Under the condition of isothermal solidification, the morphology of eutectic layer is affected by the spacing of the initial layer. With the increase of initial lamellar spacing, hypoeutectic composition: annihilation ? basic state ? 2?O ? lamellar bifurcation; eutectic composition: annihilation ? basic state ? 1?O ? 2?O; hypereutectic composition: annihilation?basic state? T- 2?O ?Tilt.(3)Changing the undercooling of the solid-liquid interface of the initial simulation research in the isothermal solidification, the results were discovered, that with the increase of undercooling, lamellar eutectic growth morphology from regular form to state of shock instability.(4)When changing interface free energy, the three interface at the contact point with the eutectic phase will change, and the system change toward the lowest free energy state.