The Investigation of microstructure evolution in electron beam additive manufacturing by phase field method

The mechanical performance of the components is highly related to the microstructure characteristics in the electron beam additive manufacturing (EBAM). The solidification process with complicated behaviors during the EBAM plays a major role in the microstructure formation. This paper is focused on the dendrite evolution in the solidification process of the EBAM of Ti-6Al-4V. A phase field model coupled with macroscopic solidification of molten pool which takes the heat transfer of molten metal and transient temperature field into consideration is proposed. The microstructure evolution and solute field distribution about columnar crystal are analyzed quantitatively. The simulated results are compared with that from the analytical model and good agreement between them has been found. It is demonstrated that the evolution of microstructure is mainly determined by the temperature gradient and solidification velocity of the molten pool. The solute enrichment behavior and severe micro-segregation of columnar crystal have great effect on the morphology and growth velocity of microstructure during the EBAM. The proposed phase field model can be used to reduce the internal structure defects and select the optimal process for the desired components of the EBAM with excellent microstructure and performance.