New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion

Rausch, Alexander M.; Gotterbarm, Martin R.; Pistor, Julian; Markl, Matthias; Körner, Carolin

doi:10.3390/ma13235517

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New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion

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Chair of Materials Science and Engineering for Metals, Friedrich-Alexander-Universität Erlangen-Nürnberg, Martens Str. 5, 91058 Erlangen, Germany

Joint Institute of Advanced Materials and Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg, Dr.-Mack-Str. 81, 90762 Fürth, Germany

Author to whom correspondence should be addressed.

Materials 2020, 13(23), 5517; https://doi.org/10.3390/ma13235517

Received: 28 October 2020 / Revised: 26 November 2020 / Accepted: 1 December 2020 / Published: 3 December 2020

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Abstract

A microstructure has significant influence on the mechanical properties of parts. For isotropic properties, the formation of equiaxed microstructures by the nucleation of new grains during solidification is necessary. For conventional solidification processes, nucleation is well-understood. Regarding powder bed fusion, the repeated remelting of previous layers can cause nucleation under some conditions that are not explainable with classical theories. Here, we investigate this nucleation mechanism with an unprecedented level of detail. In the first step, we built samples with single crystalline microstructures from Ni-base superalloy IN718 by selective electron beam melting. In the second step, single lines with different parameters were molten on top of these samples. We observed a huge number of new grains by nucleation at the melt-pool border of these single lines. However, new grains can only prevail if the alignment of their crystallographic orientation with respect to the local temperature gradient is superior to that of the base material. The current hypothesis is that nucleation at the melt-pool border happens due to remelting microsegregations from former solidification processes leading to constitutional undercooling directly at the onset of solidification. This study offers the opportunity to understand and exploit this mechanism for different manufacturing processes. View Full-Text

Keywords: selective electron beam melting; stray grains; grain structure; equiaxed; nucleation

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Rausch, A.M.; Gotterbarm, M.R.; Pistor, J.; Markl, M.; Körner, C. New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion. Materials 2020, 13, 5517. https://doi.org/10.3390/ma13235517

AMA Style

Rausch AM, Gotterbarm MR, Pistor J, Markl M, Körner C. New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion. Materials. 2020; 13(23):5517. https://doi.org/10.3390/ma13235517

Chicago/Turabian Style

Rausch, Alexander M., Martin R. Gotterbarm, Julian Pistor, Matthias Markl, and Carolin Körner. 2020. "New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion" Materials 13, no. 23: 5517. https://doi.org/10.3390/ma13235517

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New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion

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