A numerical study on microstructural features evolved across the melt pool in additively manufactured IN718 alloy

A numerically efficient 3D transient thermal-based computational framework was developed to predict the microstructure and morphology within the molten pool. The results show that a transition from curved cellular to columnar morphologies occurred while moving from the molten pool edge toward its tail, which was correlated with the ratio of local thermal gradient and the solidification rate. The higher cooling rates, at the melt pool center, are seem to favour the fine microstructure. The obtained cooling rates not only appeared to control the size of the microstructural grains but also the dendritic cell spacing within the melt pool. The microstructural features like dendrite cell spacing and the microhardness was predicted using the developed framework and validated within an error range of 7-12% and 4-6%, respectively. Moreover, a parametric study performed to investigate the effect of laser speed and power revealed that the microstructural variation was more sensitive to the scanning speed than to the input power of the simulated heat source. The obtained results from the developed numerical framework were validated with the experimentally observed values and are discussed in this paper.