Investigation On Laser Directed Energy Deposition And The Modeling Of Microstructure Evolution For TC4 Alloy

Additive manufacturing technology is a powerful tool to meet the country’s major needs and support the development of national economy,and has become one of the most active disciplines in the world’s advanced manufacturing field.In the process of laser additive manufacturing,the macroscopic molten pool morphology,temperature distribution and thermal history have significant effects on the microstructure evolution and mechanical properties of the formed parts.Therefore,it is very important to study the transient temperature field change and microstructure evolution of molten pool under different technological conditions in the laser additive manufacturing process,which is helpful to reveal the essential principle behind the technological phenomenon and lay a theoretical foundation for improving and improving the existing technological level,improving the forming quality and breaking through the technical bottleneck.In this paper,the average temperature and grain evolution of TC4 alloy in the center of molten pool under different printing process parameters were studied by laser direct energy deposition test.The results show that under the high temperature gradient formed by the molten pool,fine equiaxed crystals will be promoted to grow into columnar crystals,and the grain growth direction is perpendicular to the boundary of the molten pool.At a lower temperature gradient,new grains will heterogeneously nucleate at a high solidification rate.The grains grown in this region can effectively block the epitaxial growth of columnar grains,and it is also an effective measure to change the microstructure from columnar grains to equiaxed grains.By integrating macroscopic finite element heat conduction model,microscopic grain growth phase field model and long-short memory network,a data-driven calculation method based on physical information is proposed.In this method,the 2D/3D temperature field and microstructure of TC4 alloy at the first n moments calculated by finite element method and some experimental data are used as training sets to predict the temperature field and microstructure at the(n+1)moment,so as to realize the simulation of temperature field and grain evolution in the direct energy deposition process.The results show that the proposed data-driven calculation model can accurately predict the average temperature at the center of the molten pool,the real-time temperature distribution of the printed part and the grain evolution process in real time,and its calculation efficiency is greatly improved compared with the traditional physical model.In addition,when printing multi-layer and multi-pass shaped parts,the printing parameters with printing power of 500-600 W and scanning speed of 12-14mm/s are beneficial to promote the transformation of columnar grains into equiaxed grains or nearly equiaxed grains.This research provides new technical support for realizing the organization control of shaped parts and can promote the application of data-driven method in the field of laser additive manufacturing.