Effect of process parameters on solidification microstructure in laser additive manufacturing of inconel 718 using A new approach of numerical analysis, inverse analysis and experimental design

This study developed a novel simulation technique to predict the microstructure of Inconel 718 in laser additive manufacturing. To overcome the computational complexity of modeling the fully transient process, the problem was broken down. First, separate steady-state analyses of heat transfer, fluid flow, and melting were conducted. The results were then fed into a transient solidification model to predict the final microstructure, specifically the Primary Dendritic Arm Spacing (PDAS). A key part of the method was using experimental temperature data to accurately define the laser’s heat input in the simulation. The laser’s effective power was accurately determined using a thermocouple and a inverse analysis method. The simulation results demonstrated strong agreement with experimental data. The analysis revealed that higher laser power and slower scanning speed reduced the cooling rate, resulting in larger PDAS. Conversely, a higher powder injection rate increased the cooling rate and produced a finer microstructure (smaller PDAS). This effect of powder injection was more pronounced at higher laser powers. Furthermore, the investigation revealed a transition in solidification morphology based on energy input. A combination of low laser power (200 W) and high scan speed (6 mm/s) promoted the formation of a refined columnar and equiaxed dendritic structure, a consequence of the low temperature gradient and high solidification rate. Conversely, under conditions of high laser power (400 W) and low scan speed (2 mm/s), the microstructure evolved into a cellular and columnar dendritic pattern.