Mechanical behavior of post-processed Inconel 718 manufactured through the electron beam melting process

Abstract

The electron beam melting (EBM) process was used to fabricate Inconel 718. The microstructure and tensile properties were characterized in both the as-fabricated and post-processed state transverse (T-orientation) and longitudinal (L-orientation) to the build direction. Post-processing involved both a hot isostatic pressing (HIP) and solution treatment and aging (STA) to homogenize the microstructure.In the as-fabricated state, EBM Inconel 718 exhibits a spatially dependent microstructure that is a function of build height. Spanning the last few layers is a cored dendritic structure comprised of the products (carbides and Laves phase) predicted under equilibrium solidification conditions. With increasing distance from the build's top surface, the cored dendritic structure becomes increasingly homogeneous with complete dissolution of the secondary dendrite arms. Further, temporal phase kinetics are observed to lead to the dissolution of the strengthening γ" and precipitation of networks of fine δ needles that span the grains. Microstructurally, post-processing resulted in dissolution of the δ networks and homogeneous precipitation of γ" throughout the height of the build. In the as-fabricated state, the monotonic tensile behavior exhibits a height sensitivity within the T-orientation at both 20 and 650 • C. Along the L-orientation, the tensile behavior exhibits strength values comparable to the reference wrought material in the fully heat-treated state. After post-processing, the yield strength, ultimate strength, and elongation at failure for the EBM Inconel 718 were observed to have beneficially increased compared to the

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

“…In their subsequent paper [75], anisotropic tensile properties were reported as due to the local agglomerate of porosities rather than the intrinsic properties. The anisotropic tensile properties were further confirmed by Kirka et al [77,186]: both the tensile strength and elongation are higher tested along the building direction that tested perpendicular to the building direction in the as-manufactured sample, and these anisotropic properties almost disappear after post heat-treatment. The microstructure gradient along the building direction was first reported by Unocic et al [187], and was attributed to the height-dependant thermal exposure experienced by different parts of the component [61].…”

Strategy for Texture Management in Metals Additive Manufacturing

“…In instances where the material exhibits crystallographic anisotropy, the resulting columnar-grained material exhibits anisotropic mechanical properties similar to directionally solidified nickel-base (Ni-base) superalloys. 2 As a result, having the means of controlling texture formation in AM materials in a manner to allow either equiaxed or columnar grains as needed based upon the application of the material is beneficial.…”

High temperature oxidation of IN 718 manufactured by laser beam melting and electron beam melting: Effect of surface topography

“…After optimal heat treatment, the volume fraction of these two phases is 15-17 vol.% [15], the volume fraction of γ'' being three to four times larger than that of γ' [16]. After an ageing or a heat treatment, between 650°C and 950°C, δ-Ni 3 Nb phases, the [28,30,35]. Rao et al [40] found that HIP followed by AMS 5662 H T had a beneficial effect on the mechanical properties of AM-produced 718 alloys.…”

“…Thus, AM materials present columnar grains parallel to the build direction in LBM [24,25] and EBM processes both [26,27]. The thermal gradient induces epitaxial solidification leading to fine columnar grain architecture and dendrite epitaxial growth inside those grains, both structures are found parallel to the beam direction [28,29]. The formation of dendrites causes the segregation of alloy elements, such as niobium or titanium along interdendritic regions [30].…”