Multiple Phase Field Simulation Research Of Multi-phase Transformation During Grain Growth Of Fe-C Binary Alloy

The study of microstructure in the forming progress material is a focus in the field of materials science and engineering.Due to the limited conditions,the experimental method could not fully studies,the numerical simulation provides a new way for the development of alloy materials.The phase field method is a numerical simulation method that can directly simulate the evolution of microstructure of the material.Because it does not need to track the location of the interface,and overcomes the disadvantage and the limitation of other simulation methods,the phase field method is widely used as a powerful computational method to simulate the formation of complex microstructures during solidification and solid-state phase transformation of metals and alloys in materials science and related areas.In this work,based on the multiple phase-field model of single-pass phase transition,establish sequential function depend temperature,coupling with the sequential function phase-field equation is re-described;a new multi-phase field model is established for liquid-solid-solid multiple phase transformation by coupling the solidification transformation model with a solid state phase transformation model.Considering the influence of grain boundary defects and solute concentration on the free energy of the region,the nucleation model of solid-solid phase transformation in multiple phase transformations is established,and the anisotropic parameter equation of the grain growth in the solid-solid phase transformation was proposed.Taking an Fe-C binary alloy as an example,the author mainly analysis the continuous evolution mechanism of microstructure in the formation of the alloy.The influence of alloy solidification microstructure on microstructure evolution of solid-state phase transformation is analyzed,research the mechanism of microstructure continuous evolution of multi-time phase transition for alloy solidification and solid-state phase transformation,and the influence rule of the technological parameter on the microstructure,lay the foundation for quantitative simulation of alloy microstructure evolution.The following conclusions are obtained by simulation,the microstructure evolution of the multiple phase transformation of material is a continuous process,the last phase transformation is influenced by the previous phase transformation.The ferrite grains preferentially nucleate at the grain boundaries of the austenite grains due to the influence of nucleation energy and free energy.The grains with different nucleation sites have different shapes.The growth rate and morphology of ferrite grains are influenced by the orientation angle of the parent phase austenite grains and the new phase ferrite grains,the ferrites grow at different rates in parent austenite grains with different orientations.The ferrite grains nucleating at small-angle austenite grain boundaries have a greater rate of growth than those nucleating at large-angle austenite grain boundaries.The difference in rate of growth of ferrite grains that nucleate at large-angle austenite grain boundaries in different parent phase grains on both sides of the boundaries is larger than that of grains nucleating at small-angle austenite grain boundaries.While being transformed from austenite to ferrite,the over-saturated carbon atoms transit to the austenite phase,and this therefore results in carbon enrichment at the ferrite-austenite interface.The austenite-ferrite phase transformation belongs to the mixed controlled growth phase transformation,the diffusion of carbon and the migration of phase boundary is influenced by the temperature in the progress of the phase transformation,with the decrease of temperature,the ferrite growth pattern changes from diffusion controlled growth to interface controlled growth.