Microstructure and mechanical properties of additively manufactured Inconel 718: A comparative study between L-PBF and LP-DED

Abstract

This study aims to characterize the microstructure and mechanical properties of Inconel 718 fabricated using two different additive manufacturing processes: laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED). Similar heat treatments (HTs) including stress-relief (1065ºC for 1.5 hr), hot isostatic pressing (1162ºC under 100 MPa isostatic pressure of Ar gas for 3 hr), solution annealing (1065ºC for 1 hr), and two-step ageing (760ºC for 10 hr + 650ºC for 10 hr) are applied to both batches. Scanning electron microscopy is utilized to characterize microstructural evolution during each step of HTs for both samples. Tensile tests are performed to evaluate the mechanical properties at room temperature. Elongation to failure of L-PBF specimens is measured to be 16% lower than that of the LP-DED ones, while the ultimate tensile and yield strengths of L-PBF specimens are, respectively, 9% and 6% higher, compared to the LP-DED ones. The differences in tensile properties between two specimens are explained using microstructural and fracture surfaces analysis.