Process-structure-properties investigations for laser powder bed fused IN718 in the as-built condition

This data repository provides a central location for a body of work using one build of nickel-based alloy 718 (IN718) material and resulted in three different studies. The IN718 parts were manufactured by laser powder bed fusion using a range of laser energy densities (manipulation of processing variables) and orientations with respect to the build direction. The influence of processing variables on resulting grain structures, pore structures, and mechanical properties were studied in the as-built (not heat treated) condition. Some machining was completed to manufacture specific specimen geometries, while other specimens were left with rough as-built surfaces. All data associated with each of the three studies is included in this single data repository and organized into sub-folders. The three studies are briefly described below.The first study investigated the relationships among the high-cycle fatigue (HCF) life, surface roughness, and processing parameters. Standardized fatigue specimens were manufactured using 25 different sets of processing parameters by varying laser power, scan speed, layer thickness, and build orientation. Surface roughness measurements were conducted using white light interferometry; HCF life was measured; and fractography analysis was performed using scanning electron microscopy. Build orientation affected HCF life due to the relationship between build orientation and surface roughness. Increasing surface roughness decreased the fatigue life due to increasing number of surface-crack initiation sites. For a fixed build orientation, the laser-energy density, outside of the optimal range, decreased the fatigue life due to lack-of-fusion pores at low laser-energy densities and more spherical pores at high laser-energy densities.The second study investigated the effects of build orientation and laser-energy density on the pore structure, microstructure, and tensile properties. Three different build conditions were selected from the original 25 in the previous study, namely, the conditions that resulted in the worst and best fatigue lifetimes: 0° build orientation and 38 J/mm3 laser-energy density, 0° build orientation and 62 J/mm3 laser-energy density, and 60° build orientation and 62 J/mm3 laser-energy density. In terms of microstructure, all three conditions exhibited a predominantly <001> texture in the build direction, elongated grains and sub-grain boundaries. Build orientation (0° versus 60°) produced a difference in yield strength due to anisotropic grain morphology and effective grain size. The low laser-energy density specimens showed a significant decrease in all mechanical properties compared to the optimal laser-energy density specimens because the amount and size of the lack-of-fusion porosity.The third study chose to further down sample to only two materials conditions with the same laser energy density (62 J/mm3), but two build orientations (0° and 60°). The differences in processing parameters lead to subtle variations in pore networks and thus complicate the prediction of void-sensitive mechanical behaviors, including location of fracture. This study expands upon the void descriptor function (VDF), by accounting for interactions among neighboring pores and stress concentrations induced by non-spherical pores or voids. The modified VDF is evaluated against 120 computationally generated fracture simulations and six physical tensile specimens (three for each condition). The latter set of experiments, which include X-ray computed tomography measurements before and after deformation, enables evaluation against physically realistic and representative pores in AM metals. The modified VDF accurately predicts fracture location for 94 out of 120 simulated specimens. In the experimental data set, the modified VDF accurately predicts the location of fracture in four out of six specimens compared.

Tags: additive-manufacturing, characterization, defects, ductile-fracture, fractography, high-cycle-fatigue-life, inconel-718, laser-powder-bed-fusion, microstructure, porosity, surface-roughness, tensile-properties, x-ray-computed-tomography
Organization: National Institute of Standards and Technology