Effect of Process Parameter and Scanning Strategy on the Microstructure and Mechanical Properties of Inconel 625 Superalloy Manufactured by Laser Direct Energy Deposition

This study aimed to investigate the effect of process parameters on the microstructure and mechanical properties of Inconel 625 alloy manufactured by direct energy deposition process. The Inconel 625 samples were produced by varying the laser scanning speeds from 720 - 960 mm/min while maintaining the same the laser energy volume density. The microstructure and mechanical properties of the produced samples were evaluated, and their dimensional accuracy and mechanical properties were also analyzed in terms of the laser scanning strategy. Microstructural observations at the same energy density revealed a dendrite substructure near the laser melt pool boundaries, indicating that the dendritic microstructure was primarily formed at the beginning of the solidification of each laser bead. When the solidification further progressed into the melt pool, solidification cell substructures became dominant regardless of the laser scanning speed. The size of the solidification cell and the dendrite structure were nearly unchanged as laser scanning speed increased. This suggests that changing the laser scanning speed while maintaining the volumetric energy density does not significantly alter the solidification rates of the Inconel 625. As a consequence of the similar cell sizes, the samples produced with different laser scanning speed led to similar mechanical properties. When samples produced with two different scanning strategies, of unidirectional and 90o rotation, were compared, a better dimensional accuracy was obtained with the 90o rotation strategy, compared to that obtained with the unidirectional approach. Comparisons of mechanical properties obtained along different directions with the different laser scanning strategies revealed that the Inconel 625 produced by the laser direct energy deposition had pronounced anisotropic mechanical properties, and was the highest in strength but the lowest in maximum elongation along the laser scanning direction.