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arXiv · 1905.09537

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

Paraskevas Kontis·Edouard Chauvet·Zirong Peng·Junyang He·Alisson Kwiatkowski da Silva·Dierk Raabe·Catherine Tassin·Jean-Jacques Blandin·Stéphane Abed·Rémy Dendievel·Baptiste Gault·Guilhem Martin
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Abstract

There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable Ni-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 Ni-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 $\mu$m 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.

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Paraskevas Kontis, Edouard Chauvet, Zirong Peng, Junyang He, Alisson Kwiatkowski da Silva, Dierk Raabe, Catherine Tassin, Jean-Jacques Blandin, Stéphane Abed, Rémy Dendievel, Baptiste Gault, Guilhem Martin. 2019-05-23. Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys. https://doi.org/10.1016/j.actamat.2019.07.041

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