Journal
ACTA MATERIALIA
Volume 177, Issue -, Pages 209-221Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2019.07.041
Keywords
Hot cracking; Grain boundaries; Electron beam melting; Superalloys; Liquid film
Funding
- Investments for the Future Program [AN-10-LABX-44-01]
- Poly-Shape
- Max-Planck Gesellschaft via the Laplace project
- BIGMAX project
- DFG [SFB TR103]
- [ERC-CoG-SHINE-771602]
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There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable nickel-based superalloys. This lack of in-depth understanding of the root causes of hot cracking is an impediment to designing engineering parts for safety-critical applications. Here, we deploy a near-atomic-scale approach to investigate the details of the compositional decoration of grain boundaries in the coarse-grained, columnar microstructure in parts built from a non weldable nickel-based superalloy by selective electron-beam melting. The progressive enrichment in Cr, Mo and B at grain boundaries over the course of the AM-typical successive solidification and remelting events, accompanied by solid-state diffusion, causes grain boundary segregation induced liquation. This observation is consistent with thermodynamic calculations. We demonstrate that by adjusting build parameters to obtain a fine-grained equiaxed or a columnar microstructure with grain width smaller than 100 gm enables to avoid cracking, despite strong grain boundary segregation. We find that the spread of critical solutes to a higher total interfacial area, combined with lower thermal stresses, helps to suppress interfacial liquation. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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