Phase Field Simulation Of Dendrite Growth In Ti-Al Alloy In Heterogeneous Temperature Field

The evolution of microstructure is a complex dynamic process,which involves not only heat transfer and momentum transfer at the macroscopic scale,but also grain growth and crystal nucleation at the microscopic scale.Therefore,in addition to controlling different parameters,complex boundary conditions need to be controlled to control the solidification process of the microstructure.Computer technology has developed rapidly and is often applied in the microscopic field,becoming the main research method for alloy solidification process.Phase field method is widely used in alloy solidification simulation.Because it introduces order parameters to describe the solidification process of alloy,effectively solves the problem of tracking complex interface,and is easy to be coupled with other external fields.The phase field method uses the Ginzburg-Landau theory as the basic principle,and establishes differential equations,which can reflect the comprehensive effects of diffusion and thermodynamic driving.By establishing the differential equations of the order parameter and the temperature control equation,the phase field is coupled with the temperature field,and the microscopic simulation is effectively combined with the actual macroscopic process,so as to simulate the solidification process of metal materials is more real.In this dissertation,the development of the phase field method,phase transformation theory,are introduced.Ignored the metal solidification latent heat release,the isothermal phase field model is too simplified.In order to overcome these defects,we have established dendrite growth phase field control equations of the binary alloy with a non-uniform temperature field.Using this built model of Ti-Al alloy,the dendrite growth process are simulated and the anisotropy coefficient,and the thermal diffusion coefficient and the coupling parameter,which influence on the dendrite growth process,are studied.The relations of the various parameters with the dendrite growth speed and the morphology are analyzed.By analyzing the simulation results,the following conclusions are drawn:1)Under a non-uniform temperature field,an increase in the anisotropy coefficient can increase the growth rate of dendrites and make the dendrite morphology become developed,which promotes the growth of the secondary arms.2)Under the non-uniform temperature field,the thermal diffusion coefficient can inhibit the growth of the secondary branch of the dendrite.The increase of the thermal diffusion coefficient can slow the growth rate of the dendrite and make the dendrite morphology difficult to reach maturity.3)Under the non-uniform temperature field,the coupling parameters can promote the growth speed of the dendrite,make the growth trend of the main axis of the dendrite obvious,and can promote the growth of the secondary arm.4)Under the same values of anisotropy coefficient,thermal diffusion coefficient and coupling parameters,the increase of the cycle time step will make the dendrite morphology more obvious.These conclusions may have certain reference value for the control of the formation of Ti-Al alloy microstructure in practice.