Title: Experiments and simulations on solidification microstructure for Inconel 718 in powder bed fusion electron beam additive manufacturing

Abstract

Previous research on the powder bed fusion electron beam additive manufacturing of Inconel 718 has established a definite correlation between the processing conditions and the solidification microstructure of components. However, the direct role of physical phenomena such as fluid flow and vaporization on determining the solidification morphology have not been investigated quantitatively. In this work, we investigate the transient and spatial evolution of the fusion zone geometry, temperature gradients, and solidification growth rates during pulsed electron beam melting of the powder bed with a focus on the role of key physical phenomena. The effect of spot density during pulsing, which relates to the amount of heating of the build area during processing, on the columnar-to-equiaxed transition of the solidification structure was studied both experimentally and theoretically. Predictions and the evaluation of the role of heat transfer and fluid flow were established using existing solidification theories combined with transient, three-dimensional numerical heat transfer and fluid flow modeling. Metallurgical characteristics of the alloy’s solidification are extracted from the transient temperature fields, and microstructure is predicted and validated using optical images and electron backscattered diffraction data from the experimental results. Simulations show that the pure liquid region solidified quickly, creating a large two-phase,more » mushy region that exists during the majority of solidification. While conductive heat transfer dominates in the mushy region, both the pool geometry and the solidification parameters are affected by convective heat transfer. Lastly, increased spot density during processing is shown to increase the time of solidification, lowering temperature gradients and increasing the probability of equiaxed grain formation.« less

Authors:

Knapp, Gerry L.  ^[1];

• Search DOE PAGES for author "Knapp, Gerry L."
• Search DOE PAGES for ORCID "0000-0002-2023-992X"

Raghavan, Narendran  ^[2];

• Search DOE PAGES for author "Raghavan, Narendran"
• Search DOE PAGES for ORCID "0000-0002-6964-5718"

Plotkowski, Alex  ^[2];

• Search DOE PAGES for author "Plotkowski, Alex"
• Search DOE PAGES for ORCID "0000-0001-5471-8681"

Debroy, Tarasankar  ^[1]

• Search DOE PAGES for author "Debroy, Tarasankar"
• Search DOE PAGES for ORCID "0000-0003-1790-7066"

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+ Show Author Affiliations

1. Pennsylvania State Univ., University Park, PA (United States)
2. Oak Ridge National Lab. (ORNL), Knoxville, TN (United States)

Publication Date:

Wed Dec 05 00:00:00 EST 2018

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:

1494899

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Additive Manufacturing

Additional Journal Information:

Journal Volume: 25; Journal Issue: C; Journal ID: ISSN 2214-8604

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 42 ENGINEERING; Solidification; Additive manufacturing; Nickel-base superalloy; Electron beam; Microstructure