Effect of process parameters on solidification microstructure in laser additive manufacturing of Inconel 718 using a new approach of numerical analysis, reverse analysis and experimental design

In the present work, a novel technique is proposed for simulation of the laser additive manufacturing process to evaluate the final microstructure of Inconel 718. For this purpose, the complex physical phenomena in the process are solved by the equations of steady flow heat transfer, mass transfer, and melting-freezing. The actual laser power was modeled by installing a thermocouple in the sample and by reverse analysis (RA) method. The model was considered as a heat source in the steady simulations. The simulation model was used to calculate the primary dendritic arms spacing (PDAS) at different points of the deposit layer. It was observed that the considered model is in good agreement with the experimental results. An increase in the laser power and a decrease in the scanning speed caused a decrease in the cooling rate and thus an increase in PDAS. With the increase of the powder injection rate, the cooling rate also increased and led to a decrease in the PDAS, although the slope of its changes was greater at higher laser power. Moreover, when the laser power was low (200 W) and scanning speed was high (6 mm/s), a columnar and equiaxed dendrite structure with a short dendritic arm spacing was formed, due to the low temperature gradient and high solidification rate. However, the increase of laser power up to 400 W and the reduction of scanning speed to 2 mm/s led to formation of a cellular and columnar dendritic structure.