Effect of Heat Treatment on the Microstructure and Hardness of Ni-Based Alloy 718 in a Variable Thickness Geometry Deposited by Powder Fed Directed Energy Deposition

Abstract

Feature addition to existing parts is a trending application for Directed Energy Deposition (DED) and can be used to add complex geometry features to basic forged geometries with the aim to reduce and simplify the number of processing steps as machining and assembling. However, the mechanical properties of as-deposited Inconel 718 fabricated by Powder-fed Directed Energy Deposition (Powder-fed DED) are far lower than the relevant specifications, making it necessary to apply different heat treatment with the purpose of improving deposited material performance. In addition, the effects of heat treatments in both variable thickness deposited geometry and forge substrate have not been studied. In this study, the effect of heat treatment within the Aerospace Materials Specifications (AMS) for cast and wrought Inconel 718 on the microstructure and hardness of both the Ni-Based Alloy 718 deposited geometry and substrate are analyzed in different parts of the geometry. The microstructure of all samples (as-deposited and heat-treated) is analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS), confirming the formation of aluminum oxides and titanium nitrides and carbonitrides in the deposited structure.

Fabrication of Electron Beam Melted Titanium Aluminide: The Effects of Machining Parameters and Heat Treatment on Surface Roughness and Hardness

“…Compared to other additive manufacturing (AM) techniques, the fabrication process of Ti alloy-based parts is carried out at temperatures around 1000 • C. This temperature range minimizes or eliminates temperature gradients, thereby facilitating the production of stress-relaxed parts [22]. Similar to other additive manufacturing (AM) processes, such as selective laser melting (SLM) [23][24][25][26], electron beam melting (EBM) [27] is a powder-bed fusion technique used to directly manufacture complex-shaped geometries from a 3D CAD file; the other most popular metal additive manufacturing method is directed energy deposition (DED), where the metal powder is blown through a carrier gas and the transferred metal powder on the substrate is melted using a high energy source such as a laser beam [28][29][30]. During the entirety of the EBM fabrication process, which operates under a vacuum environment, the powder material is fed and fused by scanning a focused laser or electron beam as a heat source.…”