Multi-Phase Field Model of Laser Powder Bed Fusion Based Additive Manufacturing of IN718 Superalloy

Abstract

The present study investigates the microstructure evolution of IN718 alloy during multi (three)-layer Laser Powder Bed Fusion (LPBF) based additive manufacturing (AM), using multi-phase field (PF) modeling and experimental validation. The microstructure evolution of LPBF build has been studied via imposing fixed thermal gradient and cooling rate in case of first layer, and Rosenthal equation derived temperature field in successive layers (2nd and 3rd). The formation of dendritic gamma (γ) phase is significantly influenced by local cooling rates and temperature gradients, causing solute segregation and Nb-rich secondary phase formation in inter-dendritic regions. Simulation of successive layers show remelting of previous layers, affecting grain orientation, and secondary phase distribution, contributing to complex thermal history, wherein the final increase in secondary/ intermetallic phases (carbides, laves, and δ) are observed at the end of 3^rd layer simulation. The developed PF model accurately predicts microstructural features of the LPBF build such as Primary (PDAS), Secondary Dendritic Arm Spacing (SDAS), and misorientation angle, validating its utility as a process control tool. Finally, EBSD analysis of the as-built sample depicts varying grain orientations, consistent with the directional solidification, wherein the presence of fine grains and uniform distribution of intermetallic phases enhances the mechanical performance.