Phase-field Simulation Of Binary Alloy During Directional Solidification

The mechanical properties and durability property of the alloy lie on the solidification microstructures,control the formation of the microstructure in the casting process is particularly important. Modeling of the alloy microstructure formation using phase-field model will help to evaluate and optimize the castings processing technology so as to improve their quality.In this paper,the dendritic growth phase-field model of pure metal basing on Karma model which couple the temperature field is to present;further coupled the concentration field,the present a phase-field model of binary alloy during directional solidification which coupling of phase field, concentration field,temperature field. Using the finite difference formulas on uniform mesh to solve the control eqution,and the C code is taken to complete the phase-field simulation program,simulate the dendrite growth of pure metal in undercooled melt and microstructure evolution in directional solidification of binary alloy.The tecplot 9.0 was used to achieve the vision of results.During the dendrite growth of pure metal in undercooled melt,the connection between the dendrite morphologies and some parameters in phase-field model is very important,which include the coupling coefficient between the temperature field and the phase fieldλ,the thermal diffusivity D_T, the time parameter of interface atomic motionÏ„₀. The results show that with the increasing of the coupling coefficient between the temperature field and the phase fieldλ,the grain morphologies transformed from compact dendrite to seaweed morphologies;with the increasing of thermal diffusivity D_T and the time parameter of interface atomic motionÏ„₀, the dendrite morphologies transformed to compact morphology from slim dendrite. Furthermore,the value of interface kinetic coefficientβ₀ is determined synthetically by the coupling coefficient between the temperature field and the phase fieldλ, the thermal diffusivity Dr,the interface width W₀,the time parameter of interface atomic motionÏ„₀, and the larger interface kinetic coefficientβ₀,the larger is dendrite tip radius R_tip, the less is dendrite tip velocity V_tip.Phase field method can be accurately simulated in the process of the binary alloy directional solidification interface morphology and grain growth,the successful reproduction competition between the cellular growth during directional solidification process.The connection between the interface morphology microstructure evolution and some parameters in phase-field model is very impotant, which include the anisotropy coefficientγ,interface energyσand interface thicknessδ,the competitive selection is the dominated mode in the process of the cellular growth. The results show that, dendrite growth by shallow cellular in isotropic circumstances;after introduction of the anisotropic, with the increasing of the anisotropy coefficient, the crystal growth transformed to deep cell from shallow cell; with the increase of interface energy and interface thickness, the crystal growth transformed to shallow cell from deep cell.The stability of interface were destroyed by employing noise,the plane-cell transition and competition selection is the dominated mode in the process of the celluar growth;with the increasing of noise amplitude,cellular grains are fined,the thickness of the solute diffusion layer ahead of the interface becomes smaller,the severity of microsegregation reduces,the solute trapping is obvious.In order to confirm the result from computer simulation,the directional solidification process of Al-4.5%Cu alloy is carried on experimentally.Comparative the cross section and vertical section of testing sample with simulation results.The results show that the simulation results as same as the experimental results,which indicates that the conclusion results from the phase-field model and the simulation is successful.