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Effects of laser-energy density and build orientation on the defect structure, microstructure and tensile properties of Inconel 718 parts manufactured with laser powder bed fusion

Published

Author(s)

Dillon Watring, Jake T. Benzing, Nikolas W. Hrabe, Ashley Spear

Abstract

This study investigates the processing-structure-property relationships of Inconel 718 manufactured by laser powder bed fusion. Three di erent build conditions were selected for the Inconel 718 specimens: 0 build orientation and 38 J/mm3, 0 build orientation and 62 J/mm3, and 60 build orientation and 62 J/mm3. Distributions of defect structures (porosity) in all three build conditions were quantifi ed using X-ray computed tomography (based on measurements with a 1 mm voxel size). The volumetric porosity in each build condition was 6.91%, 0.23%, and 0.07%, respectively. Most of the pores in the low laser-energy density build condition were identi ed as lack-of-fusion (aspect ratio greater than 2:1). The morphology, size and orientation of grains were measured with electron backscatter di raction (EBSD) in three orthogonal views for all three build conditions. The 38 J/mm3 laser-energy density produced the smallest melt pool geometry and smallest grain size, but grains in all three conditions exhibited a predominantly < 001 > texture. Also, the sub-grain structure was cylindrical in nature and oriented with the build direction. The sub-grain structure consisted of dislocation networks and nanosized precipitates, plus formed gradients of misorientation within a given grain. Build orientation caused no signi cant di erence in ultimate tensile strength (1070 MPa), but there was a small di erence in yield strength (798 and 772 MPa for 0 and 60, respectively). The low laser-energy density specimens showed a signifi cant decrease in mechanical properties (640 and 775 MPa for yield and ultimate strength). Therefore, it is postulated that the defect structure dominated the mechanical properties for specimens produced with a non-optimized laser-energy density.
Citation
Additive Manufacturing

Keywords

Additive Manufacturing, Laser Powder Bed Fusion, Inconel 718, Microstructure, defects
Created June 29, 2020, Updated July 26, 2020