Aishwarya Sarker
This research presents a multiscale mechanical characterization of as-built laser powder bed fusion (L-PBF) Inconel 718 (IN718) superalloy. Electron backscatter diffraction (EBSD) confirmed a columnar grain morphology, a partial ⟨001⟩ fiber texture, and a maximum texture index of 4.89, establishing the microstructural basis for the mechanical anisotropy characterized throughout the work. Micro-tensile experiments using uniaxial and plane-strain tension geometries along the build direction (BD), 45° to BD, and transverse direction (TD), combined with digital image correlation strain measurements, revealed a consistent flow stress ordering of σTD > σ45 > σBD. The corresponding yield strengths were approximately 750 MPa and 800 MPa in the BD and TD, respectively. The Yld2004-3D non-quadratic anisotropic yield criterion was calibrated to the experimental data and incorporated into finite element (FE) simulations for ductile fracture analysis. Ductile fracture characterization using notched-tension, center-hole, and simple-shear specimens, analyzed through a hybrid experimental-FE approach, established the fracture locus across a range of stress triaxialities and Lode angle parameters, with BD identified as the critical lower-bound orientation. At the local microscopic scale, instrumented indentation testing (IIT) with Berkovich and spherical indenters revealed TD hardness values approximately 30% higher than those in BD, along with asymmetric residual pile-up morphologies consistent with directional plastic flow. FE simulations using the macroscale-calibrated constitutive model reproduced both the force-displacement responses and the orientation-dependent pile-up asymmetry. The unified experimental-numerical framework provides an experimentally grounded description of the mechanical behavior of as-built L-PBF IN718 across multiple length scales, supporting reliable structural design and performance assessment of additively manufactured components.