Research On The Simulation Of Grain Growth Of Titanium Alloy During Laser Rapid Forming

TC4 titanium alloy has the advantages of good specific gravity,high specific strength and strong anti-oxidation ability,so it is widely used in aerospace,automobile manufacturing and petrochemical industry.Laser rapid forming technology can control the growth direction and shape of the microstructure during the solidification of molten pool,and effectively improve the mechanical properties and high temperature performance of titanium alloy.In the alloy laser rapid prototyping process of TC4 titanium,the molten pool has the characteristics of non-balanced and high-temperature transient,which is difficult to observe the microstructure of molten pool by experiment.In this paper,we use the technology that combined with Cellular automata method and Finite Element method to build a macro-micro coupling Cellular Automaton-Finite Element(CA-FE)model to simulate the growth and evolution of the microstructure of the molten pool solidification of TC4 titanium alloy laser rapid forming.The FE method is used to simulate the temperature field of molten pool,and the CA method is used to simulate the microstructure of molten pool during solidification process.The temperature field results are interpolated into microcells and the dynamic process of TC4 molten pool solidification is programmed.When using the CA method to simulate microstructure growth,it is necessary to take into account the randomness of grain nucleation and the certainty of growth.The spontaneous nucleation in molten pool is described by continuous nucleation model,and the growth kinetics model of equiaxed and columnar crystal growth is established.The solid-phase ratio and the solute distribution algorithm was modified to simulate the growth of equiaxed grains and columnar grains in the uniform temperature field.The simulation results agree well with the grain growth kinetics,and the grain growth index is close to the theoretical value.The coupled CA-FE model is introduced to simulate the grain growth in the solidification process of molten pool under non-uniform temperature field.The simulation results show that there are a large number of grains in the solid-liquid interface,and there is competition between the grains.The grain-like structure is dominated by coarse columnar grains.The smaller the cellular lattice is,the more accurate the grain shape is.Compared with the microstructure of molten pool under the experimental conditions,the simulation of the whole microstructure of the molten pool is consistent with that of the actual molten pool,which is indicated that the numerical simulation results are credible.