Inconel 625 has excellent high-temperature mechanical properties and corrosion resistance in a wide range of service temperatures (up to 700 ℃). Due to this excellent combination of properties, it is widely used in aerospace, power generation and marine applications. Manufacturing complex geometric parts of IN625 is challenging by conventional manufacturing processes due to its poor workability. The laser powder bed fusion (LPBF) based additive manufacturing (AM) process is an attractive way to produce parts with complex geometry with good surface finish. Microstructure formed in laser powder bed fusion (LPBF) is highly heterogeneous due to the prevailing rapid and inhomogeneous thermal profiles. Therefore, careful selection of LPBF process parameters is required to achieve the microstructures without detrimental phases or chemical and mechanical heterogeneity. Parameter optimization by trial-and-error experiments in an LPBF-based AM is challenging due to the large number of process parameters and complex heat transfer conditions prevailing during printing. Therefore, mathematical modelling of underlying physical phenomena is advantageous for optimizing parameters for the LPBF of Inconel 625 alloy components.
In the present work, a 3-D finite element method (FEM) based heat transfer model for the LPBF of IN625 was developed to analyse the heating and cooling cycles under various laser energy densities, path planning strategies and preheating conditions. Multi-phase field method was used to simulate the microstructure evolution and predict the segregation behaviour of various alloying elements as a function of thermal boundary conditions generated by FEM simulation. The effect of temperature gradients and cooling rates was studied to understand the morphology and elemental segregation of evolving microstructure during printing. The primary dendritic arm spacing (PDAS) and elemental segregation behaviour of the resultant simulated phase-field maps are analysed by the experimental and numerical analyses. The results showed a reasonable agreement with the experimental results. Based on a detailed comparative analysis, an optimal LPBF process condition is identified to print defects-free components using Inconel 625 alloys without detrimental microstructural constituents.

Keywords: Laser Powder Bed Fusion (LPBF); Finite Element Method (FEM); Microstructure evolution; Multi-phase field method.