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Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties

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Abstract

During the electron beam melting (EBM) process, builds occur at temperatures in excess of 800°C for nickel-base superalloys such as Inconel 718. When coupled with the temporal differences between the start and end of a build, a top-to-bottom microstructure gradient forms. Characterized in this study is a microstructure gradient and associated tensile property gradient common to all EBM Inconel 718 builds, the extent of which is dependent on build geometry and the specifics of a build’s processing history. From the characteristic microstructure elements observed in EBM Inconel 718 material, the microstructure gradient can be classified into three distinct regions. Region 1 (top of a build) is comprised of a cored dendritic structure that includes carbides and Laves phase within the interdendritic regions. Region 2 is an intermediate transition zone characterized by a diffuse dendritic structure, dissolution of the Laves phase, and precipitation of \(\delta \) needle networks within the interdendritic regions. The bulk structure (Region 3) is comprised of a columnar grain structure lacking dendritic characteristics with \(\delta \) networks having precipitated within the grain interiors. Mechanically, at both 20°C and 650°C, the yield strength, ultimate tensile strength, and elongation at failure exhibit the general trend of increasing with increasing build height.

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Acknowledgements

This research is sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. The United States Government retains, and the publisher, by accepting the article for publication, acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This research was performed, in part, using instrumentation provided by the Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities.

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Authors and Affiliations

  1. Manufacturing Demonstration Facility, Oak Ridge National Laboratory, Knoxville, TN, 37932, USA

    M. M. Kirka, R. R. Dehoff & S. S. Babu

  2. Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA

    M. M. Kirka, K. A. Unocic & R. R. Dehoff

  3. Bredesen Center for Interdisciplinary Research, The University of Tennessee, Knoxville, TN, 37996, USA

    N. Raghavan

  4. Arcam AB, 431 37, Molndal, Sweden

    F. Medina

  5. Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA

    S. S. Babu

  6. Department of Mechanical, Aerospace and Biomedical Engineering, The University of Tennessee, Knoxville, TN, 37996, USA

    S. S. Babu

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  1. M. M. Kirka
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  2. K. A. Unocic
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  3. N. Raghavan
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  4. F. Medina
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  6. S. S. Babu
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Correspondence to M. M. Kirka.

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Kirka, M.M., Unocic, K.A., Raghavan, N. et al. Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties. JOM 68, 1012–1020 (2016). https://doi.org/10.1007/s11837-016-1812-6

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  • DOI: https://doi.org/10.1007/s11837-016-1812-6

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