Phase-field Simulation Of Multi-phase Transformation Of Solidification And Eutectoid Transformation Of Fe-C Binary Alloy

It is one of the hotspots in the field of material research to simulate the evolution of microstructure during solidification by phase field method.Fe-C binary alloy is the most widely used engineering structural material and is widely used in aerospace,rail transportation,petrochemical and other fields.In this paper,the phase field method is used to simulate the multiple transformation process of Fe-C binary alloy.The multi-grain growth process of Fe-C binary alloy during solidification was simulated by using the phase field model of binary alloy multi-grain growth.The effects of boundary heat flow and complex interface on the morphology evolution of dendrites were studied.The results show that the existence of lateral constraints seriously affects the evolution of microstructure during the solidification of Fe-C binary alloys.It changes the microstructure of the dendrites and the average dendrite spacing above the lateral constraints,and affects the dendrite solidification rate,solute diffusion and solute retention effects.It will have a significant impact on the final material properties.Different sizes of lateral constrains have different effects on dendrites.And the lateral constrains of the same size have different influence on dendrites with different initial dendrite spacing.This can be used as a material preparation method to prepare dendrites with a specific microstructure to improve the properties of the material.At the same time,the boundary heat flow during the solidification process has a great influence on the growth morphology and solute diffusion of dendrites.The large boundary heat flow has a strong inhibitory effect on dendrite growth,and the solute segregation at the interface is more serious.Large boundary heat extraction promotes dendrite growth and secondary dendrite development.The influence of interfacial energy and diffusion coefficient on the morphology of lamellar pearlite was studied by using the proposed binary alloy eutectoid transformation phase field model.It is found that when the free energy of the interface increases,the growth mode of the pearlite layer changes from a regular symmetry to a low-symmetry,small-amplitude slabgrowth mode,and the pearlite growth rate decreases,and the layer width of cementite phase increases,and the frontier morphology of the ferrite phase interface changes from horizontal to convex.With the increase of diffusion coefficient,the growth rate of pearlite gradually increased,and the morphology of the front edge of pearlite interface did not change significantly.In addition,by setting different lateral constraints,the effects of the complex environment on the pearlite structure during the eutectoid transformation were simulated.The results show that the lateral constraints has an important influence on the growth morphology,solute diffusion and interface advancement of pearlite during the eutectoid transformation.The lamellar pearlite grows freely before it contact with lateral constraints.And when it comes into contact with the lateral constraint,the eutectoid structure below the constraint is hindered from lateral constraint stopping growth.The eutectoid organizational passing through the lateral constraints gap is divergently grown by the action of the constraints,resulting in a large interlayer spacing.The lateral constraint of different shapes at the same size has the same effect on the growth morphology and solute distribution of the eutectoid structure.The upper surface shape of the eutectoid structure under the lateral constraint is determined by the lower surface of the constraint.The circular constraints in the middle of the calculation zone increases the effect on the eutectoid structure near the constraint as the diameter increases.Based on the existing multiphase field model of liquid-solid phase transformation and eutectoid transformation,the phase field governing equations containing the order function is re-described;establish nucleation model of eutectoid transformation base on grain boundary energy function;coupling with solute concentration field? temperature field and phase-field equation,the multi phase-field model is established which can characterize consecutiveness multi-time phase transition for alloy solidification and eutectoid transformation.Taking Fe-C binary alloy for example,simulating the microstructure continuous evolution process of multi-phase transformation of solidification and eutectoid transformation of metal materials at mesoscale.The continuous evolution mechanism of microstructure of multi-phase transformation of alloy solidification and eutectoid transformation is studied,which establishes a certain foundationfor quantitative simulation of microstructure evolution of metal materials.