Role of Post-Fabrication Heat Treatment on the Low-Cycle Fatigue Behavior of Electron Beam Melted Inconel 718 Superalloy

Abstract

Inconel 718 (In 718) specimens were fabricated by electron beam melting (EBM) additive manufacturing technique. The performance under monotonic and cyclic loading in the low-cycle fatigue regime at ambient temperature was studied. Two different conditions were considered: as-built and solution-treated and aged. All investigations were carried out on samples with machined and ground surfaces. The results revealed microstructures containing large elongated grains with a strong fiber texture 〈001〉 || BD for both conditions. Generally, the EBM Inconel 718 is characterized by high hardness and strength in the as-built state, whereas the post-process heat treatment results in a slight increase in hardness. Mechanical properties can be correlated to the fraction of strengthening phases. In terms of stress amplitudes and fatigue lives, the cyclic deformation response for both conditions is similar. Fracture surface analysis revealed crack initiation in the direct vicinity of the surfaces of the fatigued samples. The results of the current study indicate that the characteristics of the EBM process—that is, high-process temperatures and intrinsic heat treatment—potentially could pave the way for an elimination of any resource intensive post-processing treatment of Inconel 718, even in the case of cyclically loaded components.