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

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:680

Article

Kirka, Michael M.^1,2  Medina, Frank³  Dehoff, Ryan^1,2  Okello, Alfred^1,2 

[1] Oak Ridge Natl Lab, Mfg Demonstrat Facil, Knoxville, TN 37831 USA

[2] Oak Ridge Natl Lab, Mat Sci & Technol Div, Oak Ridge, TN USA

[3] Arcam AB, Molndal, Sweden

关键词: Ni-base superalloy;    Electron beam melting;    Post-processing;    Hot isostatic pressing;    Additive manufacuring;   

DOI  :  10.1016/j.msea.2016.10.069

来源: Elsevier

【 摘 要 】

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 gamma '' and precipitation of networks of fine delta needles that span the grains. Microstructurally, post-processing resulted in dissolution of the delta networks and homogeneous precipitation of gamma '' 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 degrees 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 as fabricated material. Further, as a result of post-processing the spatial variance of the ultimate yield strength and elongation at failure within the transverse direction decreased by 4 and 3x respectively.

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