Phase Field Method Simulation Of TiAl Alloy Dendritic During Solidification

TiA1 alloys have excellent high temperature strength, creep resistance and oxidation resistance, low density and specific high temperature strength, which makes them as the most attractive candidate materials for use in key high temperature components, such as automotive engine exhaust valves and aircraft engine blades. The properties of TiAl alloy and the quality of castings are intimately related to the dendritic morphology. Even if the effect of the dendritic microstructure is altered by subsequent heat treatment, they rarely fully disappear. Therefore, to master and control the solidification process of dendritic growth is the key to obtain the desired product.In addition to the theoretics and experiments, computer simulation is the third effective means and methods which has been used widely in materials science and engineering. Phase field method is known to be very powerful in describing the complex pattern evolution of phase interface. It is efficient especially in numerical treatment because all the governing equations are written as unified equations in the whole space of the system without distinguishing the interface from the mother and the new phase, and direct tracking of the interface position is not needed during numerical calculation. So, it can be used for realistically simulating morphology of dendrites during solidification under supercooling condition. In this paper, the dendritic solidification of Ti-45Al(at%) alloy is simulated by phase field modeling, and the main contents are as follows:1. Calculation of Ti-45Al alloy free energy. Based on the Thermo-Calc software, the thermodynamic parameters for Ti-45Al alloy and the Ti-Al phase diagram were calculated. The liquid and solid free energy for Ti-45Al alloy are established by using thermodamic model of phase diagram. This the main constitution of phase field model.2. Ti-45Al alloy solidification phase field model. Generally, phase field models are ideal solution or dilute solution models. Such models can not be directly applied to Ti-45Al alloy, as the Ti-45Al alloy belongs to sub-regular solution model. The phase field model for Ti-45Al alloy is built based on Ti-45Al alloy free energy and functional. 3. Simulation of the dendritic growth of Ti-45Al during isothermal solidification. The government equations for phase field model are discrete. A concrete C++ program tegether with a visualization in OpenDx is given, coupling the phase field equation and concentration equation. The dendritic solidification of Ti-45Al alloy is simulated and the results show the evolution of dendritic grow and distribution of solute and microsegregation.4. Effect of phase field parameters such as anisotropy and noise on morphology of Ti-45Al dendrites. The results show that the anisotropy has a major impact on the primary arms and noise has a directly impact on the formation of secondary arms.