Pore space characteristics and corresponding effect on tensile properties of Inconel 625 fabricated via laser powder bed fusion

Abstract

In this work, the tensile behavior of Inconel 625 parts fabricated via laser powder bed fusion (LPBF) at different laser power levels is examined, and correlated to bulk porosity as well as pore characteristics such as pore size, aspect ratio morphology, and polar orientation extracted from X-ray computed tomography (CT). Scanning electron microscopy (SEM) is employed to identify the fracture mode and origin of failure in the pulled samples. Microstructural examination on the as-built samples showed that increasing the laser power resulted in the transition of melting mode, from lack of fusion to keyhole, with an increase in part bulk density from 98.86% to 99.29%, respectively. It was found that the general bulk porosity level does not correlate directly with the Ultimate Tensile Strength (ranging between 780–820 MPa) and strain to fracture (ranging between 0.2–0.39) behavior of the parts. Detailed pore space characteristics obtained from CT datasets before and after the tensile test contributed to establishing a relationship between defects size, morphology, orientation and tensile properties of the samples. In general, it was found that strain to failure is directly influenced by pore space characteristics, while tensile strength is influenced by a combination of pore space and microstructural characteristics. This study also identified that there are systematic bias effects in the LPBF process, likely introduced by the combination of nuisance variables such as powder layer spreading and gas flow.