Multi-scale Modeling And Simulation Of Microstructure Evolution During Tungsten Inert Gas Welding Of Nickel-based Alloy Based On Cellular Automata Method

Nickel-based alloy is intensively used in aerospace industries due to its excellent comprehensive properties,and Tungsten Inert Gas(TIG)welding is one of the versatile welding techniques commonly used for joining nickel-based alloys.The mechanical properties of welding joints are closely associated with their microstructure characteristics.Investigating the dynamic microstructure evolution of welded joints is helpful to study the relationship between welding parameters and microstructure distribution,which can provide theoretical guidance for technology optimization and the obtaining of reliable joints.This paper takes the TIG welding of GH3039 nickel-based alloy as the research object,the macroscopic heat transfer model was developed,and the dynamic microstructure evolution of welded joints on different scales was studied by the cellular automata method.A macroscopic heat transfer model,a mesoscopic grain growth model of HAZ,and a microscopic dendrite growth model of molten pool were developed for the TIG welding process of nickel-based alloys.Then,a multi-scale model combining macroscopic model,mesoscopic model,and microscopic model was established by the interpolation method.TIG welding experiments of 2 mm GH3039 nickel-based alloy plates were conducted.The shape of the weld pool and the distribution of microstructures of the welded joints under different welding processes were obtained,providing experimental basis and comparative data for the subsequent numerical simulation.According to the experimental conditions,the temperature field of the TIG welding process of nickel-based alloy GH3039 under different parameters was calculated by the macroscopic heat transfer model,and the finite element model was verified by experimental results.The macro-meso coupling model was used to simulate the grain growth in the heat-affected zone during the TIG welding process.The influence of welding parameters on the grain evolution was analyzed.The results show that the grains near the fusion line were severely coarsened under the action of welding heat.And the average width and the grain size of the heat-affected zone were increased with the welding current enhanced.The macro-micro coupling model was applied to investigate the dendrite growth in different regions of the molten pool.The results show that the morphology of columnar grain in the weld depends on the epitaxial nucleation and competitive dendrite growth.The crystallographic orientation of columnar dendrites is consistent with the partially melted base metal grains.The columnar dendrite arrays with the crystallographic orientation close to the direction of the maximum temperature gradient are favorable to growth,eventually form coarse columnar grains in the weld,otherwise gradually eliminated.The multi-scale model was used to simulate the microstructure evolution of entire welded joint,and the effect of welding parameters on the microstructure evolution was studied.The predicted results were verified by metallographic and EBSD morphology.The results show that the welding parameters affect the microstructure morphology of the welded joint by influencing the grain coarsening of the heat-affected zone and the solidification conditions of the molten pool.The coarsening of the grains in the heat-affected zone resulted in the larger size of the columnar grain width in the weld.Finally,calculation programs mentioned above were further developed as a convenient and practical software for microstructure simulation of the welded joints at different scales.Based on the multi-scale model,microstructure evolution of different regions of the weld joint was investigated,and a simulation software was designed,which lays the foundation for the prediction of microstructure.