On selective laser melting of Inconel 718: Densification, surface roughness, and residual stresses

The current study investigates the effects of a wide range of process parameters on three part properties; density, surface roughness, and surface residual stresses simultaneously for selective laser melting of Inconel 718. In addition to the lack of investigations on surface roughness and residual stresses in selective laser melting of Inconel 718, process maps were developed for the selection of the best process parameters to achieve the desired values for the three parameters combined. Five laser powers, six scan speeds and three hatch spacings were chosen from the stable single tracks tests. Based on each property, a 99.5% density or a 2 μm surface roughness or the least surface tensile residual stress of 248 MPa were possible. However, no single process parameter combination was able to achieve good values for all three parameters. Prioritizing density and surface roughness, being crack initiators, over residual stresses for their effect on fatigue failure, it was found that 99.2% density and relatively low roughness of 3.5 μm are feasible at 320 W, 600 mm/s and 0.12 mm hatch spacing. Finally, opposite to the commonly observed columnar grain in Inconel 718, mixed grain structure was obtained at 600 mm/s and 1000 mm/s, indicating reduced anisotropy.