Effect of Printing Parameters and Heat Treatments on Microstructure Development of LPBF Manufactured Inconel 718 Alloy

Processing parameters of the laser powder bed fusion (LPBF) technique strongly govern achieved performances and manufacturing defects of printed alloys. In this work, it was aimed to study the effects of LPBF printing parameters and subsequent heat treatments on resulted microstructure characteristics and tensile properties of Inconel 718 alloy. Inconel samples were fabricated using three different energy densities. Then, microstructure features such as Lave phase, primary dendrite arm spacing, and internal residual stresses as microstrains of both as-built and heat-treated specimens were determined. It was found that in the range of used energy densities, alterations of phase fractions and average sizes of the Laves phase were insignificant. Decreased energy density led to microstructures with smaller primary dendrite arm spacing and thus principally contributed to enhanced yield and tensile strengths of as-printed samples, whereas increased porosity greatly deteriorated elongation. Moreover, their flow stress curves could be significantly increased by direct aging; however, typical cellular and columnar substructures occurring during the LPBF printing remained. Homogenization treatment could entirely eliminate such substructures and otherwise caused different formations of delta phase when it was performed prior to a delta process.