Effect of layer thickness on mechanical properties of laser-powder bed fused Inconel 718 parts and study of post-heat treatment response

This work investigates the impact of varying powder layer thickness on the microstructure and mechanical properties of Inconel 718 specimens fabricated through Laser-Powder Bed Fusion (L-PBF). The research aims at examining the microstructure development along <i>YZ</i> as well as <i>XY</i> planes (<i>Z</i> being the building direction) and evaluating tensile strength, microhardness, relative density, porosity, and dry sliding wear behavior of the <i>as built</i> part. The micrographs exhibit direction-dependent columnar/cellular dendritic grain morphology dominated by the local thermal gradient. As compared to the conventional wrought alloy, the <i>as built</i> L-PBFed Inconel 718 part exhibits a very fine microstructure influenced by the high rate of undercooling. The thicker powder layer leads to greater elongation (∼ 1.08% increase in fracture strain) while the thinner layer demonstrates superior strength; the increment in the average Ultimate Tensile Strength (UTS) is 140.64 MPa. All test specimens approach nearly full density; obtained relative density varies from 98.14% to 99.9%. An increase in layer thickness causes an increased degree of porosity. The decrement (∼73.6 HV₁₀) in the Vickers microhardness value is experienced at higher layer thickness. During the dry sliding wear test at room temperature, the part fabricated with a thinner layer is associated with a lower coefficient of friction. The <i>as built</i> fine microstructural morphology disappears after Homogenization Treatment (HT) followed by double-stage Aging Treatment (AT). AT promotes precipitation strengthening thus the post-heat treated specimens show improved microhardness.