Influence of Laser Power on Microstructure and Mechanical Behavior of Laser Powder Bed Fusion IN718 after Heat Treatment

Laser powder bed fusion (LPBF) is ideally suited for production of low-volume and high-precision gas turbine components. Nickel-based superalloys constitute a large fraction of the alloys used in gas turbines. Among the nickel-based superalloys, IN718 is highly popular, as it is extremely adaptable to the LPBF process. The alloy is amenable to thermal treatment and optimal properties can be obtained by precipitation hardening. This study seeks to investigate the significance of process parameters on heat-treated LPBF components. Hence, fully dense LPBF components were built at laser powers of 260W, 280W, 300W and 320W. The components were then stress relieved at 1060 °C for 60 mins, solutionized at 1060 °C for 40 mins and doubled aged at 718 and 621 °C for 8 and 18 h, respectively. The microstructures of all samples were nearly identical and consisted of epitaxial grain structure. The variation in mechanical properties between components was negligible, thereby indicating that, post-heat treatment, the effect of process parameters was negligible. The component manufactured at 320W had an optimal combination of the ultimate tensile strength (1513 MPa), yield strength (1359 MPa) and ductility (22.7%). Further, the fractured pores showed slip bands confirming dislocation activity.