Process-induced Mechanical Property Heterogeneity along the Building Direction of Directed Energy Deposited IN718 Thin-walled Parts

Abstract

Directed energy deposition (DED) makes fabrication of large technological components more achievable; however, the process-induced heterogeneity of mechanical properties restrict reliability in many applications. In this study, the correlation among parameter (lift amount), process (energy density change), and property (mechanical property nonuniformity) in thin-walled part building was investigated. The non-uniform layer accumulation was captured using in-situ imaging, and an effective energy density model was established to interpret the heterogeneous mechanical properties along the building direction of the as-built multi-layer parts. Samples closer to the bottom region of the building direction possessed superior mechanical properties (microhardness, yield strength, and ultimate tensile strength), which corresponded to a higher range of absorbed effective energy density compared to the upper regions. Within a certain range, more absorbed energy density may result in superior strength and microhardness of the layers. Deposition regions that were dominated by a relatively large negative defocus could also achieve excellent mechanical properties despite only absorbing relatively low effective energy density.