Scan strategies in EBM-printed IN718 and the physics of bulk 3D microstructure development

Andrew T. Polonsky, Narendran Raghavan, McLean P. Echlin, Michael M. Kirka, Ryan R. Dehoff, Tresa M. Pollock

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Three-dimensional (3D) characterization provides opportunities for understanding processing-structure relationships in additively manufactured (AM) materials. Bulk samples of Inconel 718 were fabricated via electron beam melting (EBM) in order to study microstructural development as a function of energy input and beam scan strategy. TriBeam tomography of bulk Inconel 718 microstructures built under steady-state growth conditions reveals the sensitivity of microstructure formation and evolution to machine process parameters. In this study, samples manufactured using a narrow range of energy input per unit build area result in varied grain morphologies and crystallographic textures. Using TRUCHAS, a thermal simulation software, the thermal history of bulk scan strategies was predicted, and combined with a calibrated microstructure-processing map to accurately predict bulk grain morphologies. The solidification parameters and the 3D measured nucleation density are used to predict the transition between columnar and equiaxed grain morphologies, providing a process map to guide AM parameter choices to locally control as-printed microstructure. A two-dimensional metric for characterizing bulk grain morphology was also found to agree well with predictions from the process map calibrated by 3D data. Combined with 3D tomography and thermal modelling, the physics of structure development were understood at a new level of detail with respect to the competing processes of grain nucleation and epitaxial growth.

Original languageEnglish
Article number112043
JournalMaterials Characterization
Volume190
DOIs
StatePublished - Aug 2022

Funding

This research was 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 and performed in partiality at the Oak Ridge National Laboratory 's Manufacturing Demonstration Facility, an Office of Energy Efficiency and Renewable Energy user facility. This research was also supported by the Department of Energy RAMP-UP program under award number 4000156470 . The MRL Shared Experimental Facilities are supported by the MRSEC Program of the NSF under Award No. DMR 1720256 ; a member of the NSF-funded Materials Research Facilities Network ( http://www.mrfn.org ). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Keywords

  • Additive manufacturing
  • Microstructure
  • Solidification
  • Tomography
  • TriBeam

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